Horse Gestation

Archive for the ‘Horse Nutrition’ Category

David W. Freeman, Extension Equine Specialist

Often, it is the way rations are fed rather than their composition that leads to digestive upset in horses. Even under the best of management, several anatomical peculiarities of the horse’s digestive tract predispose horses to digestive disorders such as colic and founder. Under poor feeding management, the onset of these disorders is almost assured. The objective of feeding management is to provide a ration with balanced nutrition in a manner which maximizes nutrient utilization while lessening the occurrence of digestive disorders.

Anatomical Peculiarities of the Equine Digestive Tract

The horse’s digestive tract can be divided into two functional divisions: foregut and hindgut. The foregut of the horse is made up of the mouth, esophagus, stomach and small intestine. It functions similarly to the digestive tract of the pig in that it is made of a simple, one-compartment stomach, followed by the small intestine. The hindgut of the horse is comprised of the cecum, large colon, small colon and rectum. The cecum functions much like the rumen of a cow in that it is a relatively large, fermentative vat housing microbes which aid digestion. These microbes break down nutrient sources that would otherwise be unavailable to the horse. Each part of the digestive tract has peculiarities that relate to feeding management.

Mouth

The mouth is responsible for the initial breakdown and swallowing of feedstuffs. Chewing reduces the size of large particle feedstuffs and breaks up the less digestible, outer coverings of grains and forages. Additionally, mastication stimulates salivary glands to release saliva, which assists in lubrication of feed for swallowing.

Since proper denture conformation is necessary for mastication, inspection of the horses’s teeth by a qualified individual should be a routine management procedure. As horses age, dental conformation can be expected to deteriorate. Consequently, older horses require more frequent inspection and treatment of teeth. Signs of poor dental conformation include excessive loss of feed while eating, positioning the jaw or head sideways while chewing and evidence of general loss of condition and thriftiness.

Esophagus

The diameter and tone of the musculature of the esophagus make it difficult for the horse to expel gas through belching or vomiting. These are predisposing features to gastric rupture, gastric distention and colic.

Stomach

Compared to most livestock, the size of the horse’s stomach is small, about 10 percent of the volume of the total digestive tract. The small size makes the rate of flow of feed material in the digestive tract through the stomach relatively fast. Gastric emptying is dependent upon volume, so large meals can be expected to pass more quickly than feed eaten continuously at low volumes. Studies have shown the majority of feed material in the digestive tract passes to the small intestine within 12 hours following a meal.

Small Intestine

The small intestine is the main site of digestion and absorption of protein, energy, vitamins and minerals. Similar to the stomach, intake level of the feed influences rate of flow of ingested matter through the small intestine. Large amounts fed in meal feedings increase rate of flow to the large intestine.

Cecum and Colon

Ingested matter not previously digested or absorbed in the small intestine flows to the cecum and colon, which make up about 50 percent of the volume of the digestive tract. The cecum and colon house bacterial, protozoal and fungal populations which function in microbial digestion of feed material in the digestive tract. Many different products of microbial digestion are absorbed by the horse.

Passage of ingested matter through the large and small colon is relatively slow. Rates of flow through the colon may take up to several days following the time feed was eaten. The diameter of different segments of the large colon varies abruptly. Additionally, the arrangement includes several flexures where the colon turns back onto itself. Anatomical arrangements such as these predispose the horse to digestive upset when nutrient flow is abnormal.

Nutrient Intake and Digestion

Water

The daily minimal requirement for water has been estimated to vary from 5 to 20 gallons. Requirements depend on factors such as environmental temperature, workload, production state and intake. Voluntary water intake can be expected to increase as the amount of ration eaten increases. Also, rations low in digestibility increase water intake. Furthermore, horses can be expected to drink more frequently when exposed to hot environmental temperatures. Horses exercising in temperate environments may have increases of 300 to 400 percent in water requirements for replacement of water that is loss in expired air and sweat. Since restriction of water intake may cause digestive upset, recommendations generally are for free choice access to clean, palatable water.

Energy

Energy is the fuel for chemical reactions which run the various systems of the body. Energy-containing compounds are part of grains, forages and many supplements. Energy is supplied in the form of starch, fiber and fat.

Starch is found mainly in grains, and as much as 55 to 85 percent of starch is absorbed in the small intestine. Starch bypassing to the hindgut is digested by microbes and absorbed as volatile fatty acids. Large amounts of starch presented to the hindgut predispose horses to colic because of gaseous products of microbial digestion and abnormal changes in gut pH and fluid balance. The amount of starch bypassing to the hindgut depends on intake level, rate of flow through the digestive tract and amount of mechanical disruption of the hard seed coats of grains. Results from nutritional studies suggest that approximately two grams starch per pound of a horse’s body weight increases starch bypass to the point of causing digestive upset. Considering starch levels in typically formulated grain mixes, recommendations are to split daily grain needs to two or more daily feedings when grain levels are greater than 0.5 percent of body weight per day (example:5 to 6 pounds of grain for a 1,000-pound horse).

Hay and pasture forage are the most common sources of high-fiber feeds fed to horses. Fiber digestion is dependent on the efficiency of digestion from microbial fermentation in the cecum and colon. Compared to cattle, horses are less efficient in digesting most sources of fiber, presumably because of faster rates of passage of ingested matter. Also, fiber digestion is dependent on the maturity and type of forage. Mature, stemmy forages are inefficiently digested, whereas digestion of immature, leafy, small-stemmed sources of fiber are similar in horses and cattle. Processing hays in cubes, pellets or chop has little effect on digestibility but may be helpful for feeding to older horses with poor teeth condition.

Fat is a component of most feedstuffs. Nonsupplemented grain mixes typically have minimums of 2 to 3 percent fat. Adding additional levels of fat in formulations for grain mixes has become a common practice. This supplementation increases the energy concentration of grain mixes while decreasing the amount of starch. Therefore, fat-added feeds have advantages of being more concentrated in energy and safer because of containing less starch as a total part of the energy-containing compounds.

Protein

Proteins supply amino acids. Amino acids are used in a variety of body processes, largely for developing and maintaining lean body tissue. Amino acids are absorbed intact in the small intestine, while protein in the hindgut is absorbed primarily as ammonia. Some of the essential amino acids must be absorbed intact because the horse’s body cannot synthesize them. Thus, increasing the efficiency of protein digestion in the foregut is desirable. Total tract and prececal digestibility vary with protein source and protein concentration in the diet. Total tract protein digestibility of feeds typically ranges from 40 to 70 percent. As much as 75 percent of protein in soybean meal is digested in the foregut, whereas estimates for prececal forage digestibility range from near zero to 20 percent. Slowing the passage of protein by splitting daily needs into two or three feedings per day will increase amino acid absorption in growing horses.

Minerals and Vitamins

Mineral and vitamin imbalances, deficiencies and toxicity can cause a multitude of health disorders in the horse. In many cases, recommendations are based on limited research or requirements and have not been established because of absence of research.

Calcium and phosphorus are the two minerals which have received the most research attention. Horses require more calcium than phosphorus and are susceptible to skeletal system disorders when fed less calcium than phosphorus. Additional minerals receiving considerable attention in recent research include copper and zinc, also because of implications related to skeletal growth disorders.

Research information on vitamin requirements is largely absent in equine nutrition. Fresh forage is a major source of vitamins, and most needs are considered met when horses have access to quality hay or pasture. Vitamin A is the most commonly supplemented vitamin in rations, partially because of the large needs for production and growth. Vitamin D is also routinely added, especially to horses who do not receive fresh forage. The needs for vitamin D are less than for vitamin A, and recommended upper levels of safe intake are much lower.

Requirements of the other fat-soluble vitamins, E and K, are less clear, and clinical deficiencies and toxicity are not as commonly observed. Sources of vitamin E are routinely added to equine diets to guard against deficiencies which cause myodegeneration, or breakdown of muscle. Vitamin K requirements are presumed to be met by synthesis of vitamin K sources by microbes in the cecum and colon. Requirements for B vitamins are largely unknown. B vitamins are assimilated by microbes in the horse’s cecum and colon, and these sources are assumed to meet the needs of most horses. However, B vitamin supplements are routinely added to diets of exercising horses because of the role of B vitamins as catalysts for energetic pathways.

Feeding Management Implications

Water

As discussed previously, water intake is important for maintenance of normal body processes. Restrictions in water, such as that caused by voluntary reductions in response to abrupt decreases in environmental temperature or changes in water source, may cause an increase in the incidence of colic. Water intake should be monitored because of numerous health problems associated with dehydration. Monitoring water intake requires frequent inspection of water sources, including the function of automatic waterers. In general, horses should be allowed free access to fresh, palatable water. Some horses may drink so much as to cause digestive upset if given free access immediately prior to performing and recovering from intense exercise, and it is recommended that water should be provided in smaller amounts at frequent intervals during these times. Regardless, dehydration can be a serious problem in exercising horses. Therefore, it is important that water is offered frequently and that intake is monitored.

The Need for Long-Stem Forage

Rations for horses should be forage based. Generally, horses should have access to pastures, hays or coarsely processed forage at minimal levels of 0.75 percent of body weight per day. Among other benefits, incorporating long-stem forage into rations increases particle size of ingested matter, thus slowing rate of passage. It also increases dry matter intake, thus stimulating water intake. Additionally, incorporating long-stem forage reduces the frequency of behavioral problems such as tail chewing, wood chewing and feeding on excrement. Grain mixes should be formulated to balance and add to the value of forages. High quality forages are more concentrated in nutrients and more efficiently digested; thus, lower levels of grain supplementation are necessary. Feeding forages containing weeds, insects, large amounts of indigestible fiber or foreign material will predispose the horse to digestive upset.

Meeting Requirements with Balanced Rations

Nutrient balances are important for all diets. However, horses in production, growth or performing high levels of athletic competition or work are most likely to develop observable disorders from ingesting an imbalanced ration. A feeding management plan requires knowledge of requirements, an ability to formulate rations and knowledge of utilization of different feedstuffs.

Growing horses, exercising horses, gestating and lactating mares and stallions during breeding programs require more nutrients than horses at maintenance. Feeding management plans should consider these differences, and farm facilities should separate horses into different production classes. The feeding management plan should also consider the number of different classes of horses, the ability to correctly add supplements on-farm, the ability to feed different numbers, as well as types of rations, feeding costs and the availability of different feedstuffs.

Meeting requirements also requires knowledge of nutrient content of grains, forages and supplements. Rations have successfully incorporated many different combinations of fresh forage, hays, grains and supplements. However, feedstuffs contain different levels of energy, protein, minerals and vitamins. Knowing the expected nutrient profiles of selected feedstuffs will direct supplementation to meet needs without causing deleterious effects on performance or health.

Estimates of the nutrient content of feedstuffs can be obtained from feed tags on grain mixes, feedstuff tables in animal nutrition texts, professional nutritionists or chemical analyses. Because of the variability in forages, farms using significant amounts of hay from a single source should have hay sources routinely tested for protein, fiber and minerals.

Maintaining a Nutrient Balance in Rations

Feedstuffs contain differing levels of nutrients. Grains are relatively higher in energy than forages, some byproduct feeds contain high levels of protein, and mineral and vitamin levels can be expected to vary greatly between different feed sources. Because of these differences, changing sources or amounts of feedstuffs will alter the nutrient balance in rations. Commercially formulated grain mixes are routinely supplemented with nutrients, so the different ratios of grain and hay and different hays that horses are fed will not adversely alter the nutrient profile of the total ration.

Some feeding managers are equipped to properly supplement rations by on-farm addition of ration ingredients, whereas others routinely make uninformed decisions to add many different types of nutrients to the base rations. The unknowledgeable addition of ingredients can easily cause numerous irreversible health problems in all classes of horses. Two problems frequently observed with improper ration adjustments are supplementation without knowledge of need or level of intake before supplementation, and supplementing for one ingredient without recognizing the additional amount of other ingredients a supplement may contain.

Additionally, horses should not be expected to self-regulate their need for most nutrients. This is evidenced by horses overconsuming energy to the point of digestive upset. In addition, horses do not regulate most of their mineral needs under free-choice management. Additional needs for minerals should be met as part of a formulated ration at regulated intakes. The exception to this rule is the free choice offering of salt, or sodium chloride. It is generally recommended that all classes of horses be provided salt, either plain or trace-mineralized, in block form with the constraint that free-choice, palatable water is available at all times.

Feeding to Desired Body Condition

Horses in a positive energy balance will store energy as fat, and body fat is reduced when the ration does not provide sufficient nutrients to maintain energy balance. Accurately assessing the fat cover allows for visual appraisal of the energy status of a horse. In general, most horses should be fed a balanced ration at levels which produce a moderate to fleshy body condition, thus avoiding an extremely thin or obese condition. Because horses in similar production and weight classes will vary in their nutrient needs, routine assessment of body condition of each horse is necessary. While horses in similar production and weight classes are commonly grouped together, those individuals with abnormally high or low body condition may need to be separated further to meet individual needs.

Assessing Energy Sources, Levels and Utilization in Feeds

Voluntary intake in horses appears to be influenced by a number of factors: weather, palatability of feed, interaction with other horses, and energy intake, among others. Regardless, if allowed free access, most horses will consume enough grain to cause digestive upset. As discussed previously, the most common problem with overeating is the consumption of too much starch in a single feeding. Grains vary in the amount of starch. For example, corn has more starch per pound than oats. Also, there may be differences in foregut digestibility of starch between different grains. Depending on intake, more starch in oats may be digested prececally than corn.

The Value of Processing Feeds

Processing increases digestibility of hard seed-coat grains and assists in intake of ingredients with different particle sizes in a mix. Feeding finely processed rations such as ground mixes is not recommended because it may decrease palatability, increase dust, increase incidence of gastric upset and increase the rate of flow of nutrients through the digestive tract.

Pelleting, micronizing, flaking, rolling, cracking, wafering and extruding are examples of processing methods that are acceptable. Several different pellet sizes have been successfully fed to horses, most ranging from 0.2 to 0.75 inches in diameter. Often, forages are recommended to be fed loose so behavioral abnormalities resulting from boredom are reduced. However, cubed (1 1/4 inch in diameter) hay can be fed as the sole source of forage with no reported incidence of behavior abnormalities.

Processing can cause several differences in rate of intake and utilization of nutrients. Completely pelleted rations are consumed faster than textured grains. Extruded feeds are consumed more slowly than pelleted or textured grain mixes. Texture and hardness of grains will determine the value of processing. Small seed grains with hard seed coats, such as milo and wheat, should be processed to increase utilization of nutrients. The benefit of processing softer seed-coated grains, such as oats, is much less. Also, the value of processing grains can differ between horses. Horses with poor denture conformation, such as older horses, may benefit more from processed feeds than others. Also, the value of processing is increased when feeding large quantities of grain to horses with limited capacity, such as rations fed growing horses to obtain maximum gain.

Total rations may be mixed, ground, and processed by pelleting or extrusion to make a complete feed. Complete feeds have several advantages, most related to ease and convenience of feeding. However, it is most commonly recommended to provide at least 0.75 pounds per 100 pounds of body weight in long-stem forage to supplement these complete feeds to guard against tail chewing, coprophagy and gastrointestinal problems.

Feeding by Weight of Ration Instead of Volume

Feeding by weight will decrease the chance of overfeeding due to differences in weight per volume of different feeds and different processing methods. For example, corn weighs more per volume than oats, and pelleted feeds weigh more per volume than textured feeds. Consequently, it is recommended to weigh feed periodically to insure accurate monitoring of intake. This is especially important when changing feed sources. One of the most common causes of digestive upset is overfeeding energy in a single feeding because differences in weight of grain mixes were not taken into account.

Feeding Frequency

In many ways, the horse’s digestive physiology is best suited for a continuous, low-level supply of feed. However, for management, housing and production needs, most horses are meal-fed. Meal-feeding large amounts of starch increases starch bypass into the cecum and colon. As discussed previously, large amounts of starch presented to the hindgut increases the frequency of digestive upset. Therefore, it is recommended to split grain into two daily feedings when the daily amount of grain exceeds 0.5 percent body weight (5 pounds grain per 1,000-pound horse). Those feeding grain to horses at levels of or above 1 percent of body weight per day should consider splitting amounts into three portions per day. Meal feedings should be separated as much as possible -- that is,10 to 12 hours between a.m. and p.m. feedings for two daily meals.

Reducing Rate of Intake

Reducing rate of feed intake may be desirable if horses bolt their feed, resulting in choking or digestive upset, or if reducing rate of intake decreases competition in group-fed horses. When horses are fed in individual feeders, methods used to slow feed intake in abnormally fast eating horses have included spreading grain out in shallow troughs, placing several large stones in the feed trough, requiring the horse to eat around them or using spaced bars or feeding rings to limit access to the feed trough. As discussed previously, processing of the ration also influences the rate of intake. While the fiber content or size of pellet does not seem to affect rate of intake, increasing pellet density, or hardness, has been shown to slow intake of a pelleted grain mix.

Group versus Individual Feeding

In groups, horses tend to do what other horses do. One horse eating encourages others to eat. Similarly, appetite can be stimulated in individually housed horses by allowing a horse to observe other horses eating.

Competition among horses in group-fed situations may allow some horses to consume more feed than needed while others are not allowed access to adequate amounts. To reduce competition among horses, group-housed horses should be fed grain in individual feeders that are spread out over a large area, that is, 50 feet between feeders. Additionally, slowing the rate of intake of grain by reducing the desire to eat may reduce competition. Supplementing pastures with free choice hay in times of limited forage production may slow rate of intake of grain because horses may not be as hungry at meal time.

However, even under the best management, horses low on the herd pecking order or stressed because of conditions such as old age or lameness will need to be housed separately to reduce competition.

The Need to Make Gradual Changes in Rations

Grains and hay differ in nutrient content. Changes in the intake level and the physical form of rations should be done gradually over several days to weeks. This practice allows the digestive tract time to adapt to different levels and physical forms of nutrients and is especially important when feeding energy-dense rations. As such, grain amounts should be increased incrementally when changes in management require an immediate need for more energy. For example, increase grain one-half pound every two to three days until energy balance is met. For similar reasons, introduce horses to pastures with large amounts of lush forages by limiting access for several days.

Incorporating the Feeding Management Plan with Total Farm Management

The source, ingredient mix and number of rations will depend on numerous management practices that interrelate with the feeding program. The need to transport to events, timing of exercise schedules, labor constraints and costs are significant management factors which affect feeding management. Deworming, vaccination schedules, ectoparasite control and general hygiene are examples of health practices that relate the nutritional plans and the well-being of the horse.

Effective management also involves treating each horse as an individual. As such, effective management requires an accurate, quantitative record-keeping system that allows for individual assessment of each horse.

David W. Freeman, OSU Extension Equine Specialist

Introduction

Horses are fed a variety of feeds. Diets range from 100 percent pasture forage to 100 percent completely processed mixes. Most horses are fed forage in the form of hay or pasture in combination with a grain mix. The choice of feed is influenced by the horses’ requirements, availability of pasture, availability and cost of commercially prepared feeds, feedstuffs traditionally fed and use and management of the horses. Nutrients should be supplied in the amount, form and method that safely and efficiently meet requirements. Correctly supplying nutrition to horses requires knowledge of requirements, feeds and nutritional management.

Most horse owners rely on formulated feeds from commercial sources, or on a nutritionist’s support for customer formula mixes. Even so, in order to make accurate decisions, horse owners should have a general knowledge of nutrients, how nutrient needs change with different production and use classes of horses, and how to determine if nutrient supply is aligned with requirements.

Feedstuffs

Feeds for horses can be divided into forage, grain and grain byproduct, and supplement categories. Tables 1 through 3 provide average nutrient concentrations of different feedstuffs. Feeds displayed are not intended to represent ideal ingredients. The tables are intended to show how nutrient content of different feeds vary. The nutrient content of feedstuffs can be estimated from values reported in feed databases and nutrition texts. Values listed in feed tables are averages. Some feedstuffs are highly variable in nutrient content from source to source, so averages may be of limited value. Accuracy of feed tables will increase when the values represent large numbers of samples on feedstuffs with low variability from source to source.

Feedstuffs can be analyzed for nutrient content at feed testing labs. Testing will be of greater value for large amounts of a feed that will be fed for a long period of time, such as a yearly hay supply. Proper sampling techniques of feeds that are to be tested will increase accuracy of test results, especially with forages. Information on feed testing laboratories and sampling techniques can be obtained with the assistance of local cooperative extension professionals.

Forages

Forages are long stem, high fiber feedstuffs. Forages include growing plants and plants that are harvested and processed into hay, haylage and hay cubes. Compared with grains, forages generally contain lower concentrations of digestible energy, higher levels of fibrous carbohydrates and lower levels of nonfibrous carbohydrates. Nutrient content will vary between forage types and stages of growth.

Legumes, such as alfalfa, will contain larger concentrations of protein than grass species and generally will have a digestible energy value of 10 percent to 20 percent more than a grass in the same growth stage. Legumes also will contain higher levels of some minerals and vitamins. Improved grass species such as bermuda grass; bluestem; and cool season species like wheat, rye, and ryegrass, will typically contain more nutrients per weight than native prairie grasses. Nutrient levels of pastures and hays identified as prairie and native grass will vary greatly because of the many different grasses that may be represented.

Grains and Grain Byproducts

Grains are seeds harvested from plants. Grain byproducts are portions remaining after the removal of certain parts of the grain, for example, the removal of sugar and starch from the grain kernel. Typically, grains are higher in starch and lower in fiber than forages. Barley, oats, corn and milo are four commonly fed grains. The starch, fiber, protein, mineral and vitamin content of byproducts vary greatly. Wheat midds, rice bran, distiller’s grains, beet pulp and soybean hulls are byproducts that are commonly used as portions of grain mixes. Other byproducts, such as soybean meal, are high protein feeds and are used as supplements in grain mixes to increase the protein value of a mix. Feeding of grains and grain byproducts with significant digestible energy values must be regulated as over consumption leads to digestive upset.

Supplements

Supplements are added to rations to balance specific nutrients or to raise levels of certain substances. Premixes are routinely added to increase protein, mineral and vitamin amounts. Vegetable oil may be added to increase the fatty acid content and to raise the energy concentration. Other ingredients may not have as direct an effect on nutrient balance. These compounds are termed additives and may include compounds with reported health benefits outside of what is known as the nutritional requirements for horses.

Commercially Prepared Feeds

Commercially prepared horse feeds typically contain a mixture of grains, grain by-products, high fiber feedstuffs, high protein feeds, minerals, vitamins and additives. Most are designed to be fed in combination with forage and will indicate such on the feed bag. Others are tagged as complete feeds, which are formulated to be fed solely without need for daily intake of forage. Feeds may be formulated to best be fed to specific classes of horses, i.e. mixes formulated to be fed to growing horses may have more protein and minerals per weight of feed than mixes intended to be fed to mature, non-producing horses.

Commercially prepared grain mixes will have a feed tag that contains a list of ingredients and the guaranteed levels of certain nutrients contained within the feed. Nutrient levels are expressed as concentrations in the ration, for example, minimum percent crude protein. If a feed is tagged as 14 percent crude protein, each pound of feed will contain a minimum of 0.14 pounds of crude protein. The list of feed ingredients will provide additional evidence of other nutrients, such as minerals, vitamins and additives not included in the guaranteed analysis of nutrient content.

Evaluating Rations

In order to evaluate how well feeds align with requirements, one must have estimates of the horse’s nutrient requirement and the intake and nutrient content of all the feeds in the diet. Estimates of requirements can be found in textbooks and reports that base values on nutritional research. In practice, energy needs are estimated by feeding levels that maintain horses in appropriate fat cover. Body condition scoring systems are used to index fat cover.

Estimating the intake of a meal-fed diet is fairly simple if there is access to a scale designed to measure weights typical of a rationed diet. Estimating intake from a standard volume, such as a feed scoop or coffee can, is unreliable. Feeds vary in density because of processing and ingredients. Intake of free choice hay can be estimated by observing disappearance over several days and making the assumption that intake is similar between horses when group fed. Estimating intake of pasture is more difficult, as daily voluntary intake of feed varies with horses, feedstuffs offered and environmental conditions.

When forage is unlimited, voluntary dry matter intake is expected to range from less than 1.5 percent to greater than 3.0 percent of body weight per day. Higher intakes are expected when young, growing plants are available. Nutrients in young, growing plants will also be more digestible. Intake and nutrient digestibility also will vary between plant types. In general, plants with higher levels of digestible fiber will be more readily consumed as compared to forages high in cellulose and lignin.

Horses can easily become undernourished when the only source of nutrition is pastures with small supply of forage or only forages that are indigestible. Conversely, diets containing energy-dense grains or access to lush pastures should be regulated by rationing harvested feeds and access to grazing. Overeating leads to excessively fat body condition and increased incidence of colic and founder.

Generally, diets are formulated to meet energy demands when fed at levels around 70 percent to 85 percent of the expected maximum daily dry matter voluntary intake, resulting in as fed dietary intake of grain and hay diets of 2.5 percent to 3.0 percent of body weight per day. Growing horses may consume more as a percent of body weight than mature horses. Diets with feedstuffs low in digestible energy will be fed in larger amounts as compared with diets with higher digestible energy value. Diets formulated for horses with elevated energy needs, such as lactating mares and heavily exercising horses, will be more energy-dense than maintenance diets. Diets with high moisture content, such as immature, small grain forage, will be consumed at larger amounts because of the high percentage of water associated with the forage intake.

Routine Mathematical Conversions

To be complete, ration evaluation requires knowledge of horse physiology, feedstuffs and feeding plans. Horse owners are cautioned that mathematical evaluations alone do not account for what can be safely fed under different feeding systems. Nonetheless, there are several routine evaluations that can be conducted in order to check the alignment of the diet with requirements.

The amount of dietary intake and the nutrient densities of that intake should be expressed in the same units, that is, as a dry matter or as-fed basis. When expressed as-fed, the nutrient densities are representative of feed that contains normally occurring environmental moisture levels. Feed tags provide a guaranteed analysis on an as-fed basis. If a tag lists crude protein at 12 percent, each pound of feed that is fed will provide 0.12 pounds of protein.

Nutrient densities are expressed on a dry matter basis when the normally occurring environmental moisture of a feed is removed by drying in forced air ovens. Nutrient analyses from testing laboratories may express nutrient densities on a dry matter basis. Providing analyses on a dry matter basis allows for a more accurate compilation of estimates than as-fed because it removes the influence of differing moisture levels between samples.

Most feed analysis reports provide a percent moisture and percent dry matter of the tested sample and will list results on an as-sampled and dry matter basis. The as-sampled values can be assumed to be the same as fed if the sample is fresh and contains similar moisture levels as what is fed. The percent moisture and percent dry matter of a feed equals 100 percent. Ten pounds of a feed as-fed that contains 5 percent moisture equals 9.5 pounds of feed on a dry matter basis (10 pounds as-fed X 95 percent dry matter). Because water is removed, the nutrient densities of a dried feed will be larger than the corresponding nutrient density on an as-fed basis. Ten pounds of feed containing one pound of protein as-fed equals an as-fed protein density of 10 percent (1 pound of protein divided by 10 pounds of feed). If that feed contains 10 percent moisture, the protein density on a dry matter basis of feed would be 11 percent (1 pound of protein divided by 9 pounds of dried feed).

To convert nutrient densities from a dry matter to as-fed basis, multiply the nutrient percentage as listed on a dry matter basis by the percent dry matter of the feed. For example, a feed analyzed to contain 0.7 percent calcium on a dry matter basis that is 95 percent dry matter would contain 0.66 percent calcium on an as-fed basis (0.7 X 0.95). To convert a nutrient density value expressed as-fed to a dry matter basis, divide the as-fed value by the percent dry matter. For example, a feed analyzed to contain 12 percent crude protein as-fed with a dry matter estimate of 90 percent would contain 13.3 percent crude protein on a dry matter basis (12 ÷ 0.90).

The other check involves standardizing units of weight. It is common for nutrient requirements to be expressed in metric units, that is, grams, and measurements of amounts fed to be in U.S. measurements,or pounds. There are 454 grams in a pound. If nutrient requirements are provided in metric units, the easiest conversion may be to convert pounds fed to grams. Then, the amounts can be multiplied by the percentage of nutrient of interest and compared to the requirements.

Another frequently needed conversion is converting a nutrient density expressed as a percent to parts per million (ppm), or vice versa. Units expressed as percent are converted to ppm by multiplying the percent of nutrient in decimal form by 10,000. To convert a nutrient density expressed as ppm to percent in decimal form, multiply the ppm by 0.0001. An ingredient listed as 4 percent of the diet equals 400 ppm (.04 X 10,000). Four hundred ppm equals 4 percent (400 X 0.0001).

Example One: Comparing What is Fed with Estimated Requirements

Compare the dietary intake of crude protein, calcium and phosphorus in Table 4 with estimated requirements for crude protein, calcium, and phosphorus of 500, 20, and 15 grams, respectively. The horse is fed 10 pounds of hay each day with 5 pounds of the grain mix. Are the estimated requirements for crude protein, calcium and phosphorus aligned with the requirements?

The nutrient content listed in Table 4 is on an as-fed basis, as are the amounts of feed, so no conversions between dry matter and as-fed basis are necessary. Ten pounds of hay would equate to 4,540 grams of hay, and 5 pounds of grain equates to 2,270 grams of grain (5 pounds X 454 grams/pounds). Add the amount of hay crude protein to the amount of grain crude protein to determine the amount of crude protein fed per day. The amount of hay crude protein is determined by multiplying the amount of hay by the percent protein:

Amount of crude protein supplied by hay = 4,540 grams of hay fed X 8 percent crude protein = 363 grams of crude protein.

Amount of crude protein supplied by grain mix = 2,270 grams of grain fed X 10 percent crude protein = 227 grams of crude protein.

Total ration crude protein = 363 + 227 = 590 grams, which compares to the estimated minimum requirement of 500.

Completing similar exercises for calcium and phosphorus provides estimated intakes of about 25 grams of calcium and 18 grams of phosphorus. So fed levels of crude protein, calcium and phosphorus are at or slightly above the estimates for requirements.

Example Two: Altering the Nutrient Densities when Combining Feeds

For the second example, determine the change in nutrient density of a ration when 5 pounds of a grain mix are fed with 7 pounds of oats (Table 5). Also, determine the amount of each nutrient that is fed in the final mix.

To obtain the nutrient densities of the combined grain mix and oats, first determine the relative percentage that each feedstuff supplies to the total. The total amount as-fed is 12 pounds. The grain mix makes up 42 percent (5 pounds ÷ 12 pounds) and the oats 58 percent (7 pounds ÷ 12 pounds) of the final mix. Then, multiply the percentage contribution of each feedstuff by the nutrient density of that feedstuff and add the percentages together.

Crude protein percentage of the final mix = (0.42 grain mix X 10 percent crude protein) + (0.58 oats X 11.5 percent crude protein) = 4.2 percent + 6.7 percent = 10.9 percent

Calcium percentage of the final mix = (0.42 X 0.5 percent) + (0.58 X 0.1 percent) = 0.27 percent

Phosphorus percentage of the final mix = (0.42 X 0.4 percent) + (0.58 X 0.4 percent) = 0.4 percent

Amount of crude protein fed = 12 pounds X 10.9 percent = 1.3 pounds

Amount of calcium fed = 12 pounds X 0.27 percent = 0.0324 pound = 14.7 grams

Amount of phosphorus fed = 12 pounds X 0.4 percent = 0.048 pounds = 21.8 grams

Adding oats did not alter the crude protein percentage or phosphorus percentage to any significant amount. However, the percent calcium was altered more. The combination of feeds resulted in more phosphorus than calcium being fed, possibly so much that an imbalance of calcium and phosphorus would occur in the total diet.

Example Three: Topdressing Supplements

Many horse owners supplement rations with vitamin or mineral supplements. The third example provides a method for determining the need for vitamins E and D. Vitamin amounts are usually listed as International Units, abbreviated as IU.

In this example, the horse’s requirement is estimated at 800 IU of vitamin E per day. The horse is receiving 15 pounds of hay estimated to contain 11.6 IU vitamin E per kilogram as fed, and 4.5 pounds of a grain containing 160 IU vitamin E per kilogram as fed. The first step is to standardize the weights fed with the listed concentrations. A pound is equivalent to 0.454 kg, so multiply the amounts in pounds by 0.454 to obtain equivalent weights in kilograms. Fifteen pounds is about 7 kg, and 4.5 pounds about 2 kg.

Base ration Vitamin E intake:

Hay: 7 kg x 11.6 IU/kg = 81.2 IU/day

Grain: 2 kg x 160 IU/kg = 320 IU/day

Total vitamin E intake: 81.2 IU + 320 IU = 401.2 IU/day

Supplemental vitamin E required:

Daily vitamin E requirement: 800 IU/day

Base ration vitamin E intake: 401 IU/day

Supplemental vitamin E required: 399 IU/day

The actual amount of supplement needed to supply the vitamin E will depend upon the vitamin supplement because vitamin concentrations of supplements vary considerably. If the label on the selected supplement states that it contains 6,400 IU vitamin E/pounds of supplement, then 0.0625 pounds/day or 28.4 grams of supplement is required to provide the vitamin E difference of 399 IU/day. This amount was calculated as follows:

399 IU supplemental vitamin E required per day ÷ by 6,400 IU vitamin E/pound of supplement = 0.0625 pound x 454 grams/pound = 28.4 grams/day.

The supplement may also provide other nutrients aside from the one targeted for supplementation. The intake of other nutrients should be calculated in order to avoid over supplementation. In this example, the supplement also provides 800 IU vitamin D/pounds, which is equivalent to 1,760 IU/kg. Therefore, 28.4 grams of the supplement provides 50 IU/day of vitamin D (1,760 IU Vitamin D/kg x .0284 kg/day = 50 IU/day of vitamin D). The vitamin D requirements are estimated at 3,300 IU/day.

The hay was estimated to contain essentially no vitamin D. The grain mix label indicates a vitamin D concentration of 1,700 IU vitamin D/kg as-fed. Therefore, 2 kg of the grain mix provides 3,400 IU of vitamin D/day. The total vitamin D intake, vitamin supplement plus grain mix plus hay, is 3,450 IU/day (50 IU + 3,400 IU + 0 IU = 3,450 IU/day). In this example, topdressing with the vitamin supplement adequately provided needs for vitamins A and D.

David W. Freeman, Extension Equine Specialist

The success of any breeding program depends partially on correct nutritional management of broodmares. Past history reveals the common use of many different nutritional management practices for broodmares. Many of these have contributed to increased cycles per conception, low-foaling rates and below average foal growth. Studies provide information which enables nutritionists to refine recommendations of nutrient requirements for maximum broodmare performance. The broodmare owner should supply the amount and balance of nutrients that will aid in maximum conception rates and best meet the needs during gestation and lactation. Nutrients of concern include energy, protein, minerals and vitamins.

The Open Mare

The mare owner’s objective for this group of mares is high conception rates early in the breeding season with a low ratio of cycles bred per conception. The sooner a mare has conceived, the quicker she can be removed from the breeding program, and the more economical it is to the mare owner. This is especially true when mares are taken to a breeding farm. Mares that are settled on the first cycle will cost the owner less in care and better enable the stallion manager to make efficient use of labor and available stallion semen.

Body Condition and Energy Needs

A major problem with open mares is that many enter into the breeding season in poor body condition. Body condition is visually identified by observing fat cover along the neck, withers, back, shoulder, ribs and tailhead (See HorseQuest Learning Lesson:How to Body Condition Score Horses for more information). Mares in a low-body condition have little to no fat cover along the sides of the neck or withers, behind the shoulder or around the tailhead. Also, the backbone and a faint outline of the ribs can be seen. Mares entering into the breeding season in low condition require more cycles per conception, have lower conception rates and are later in their transition into the ovulatory season, as compared with open mares in a fleshy condition. Mares in fleshy condition will have a slight crease down the back and will have fat covering the outlines of the ribs. Noticeable amounts of fat can also be seen along the sides of the neck and withers, and the fat deposited around the tailhead feels soft.

Energy content of the ration is of major concern because of the influence of body condition on reproductive performance. The amount of energy needed per day will depend largely on how much the mare weighs and whether she needs to gain weight before the breeding season. A 1,200-pound mare maintained in fleshy body condition may meet her energy needs on an all-forage diet. If access to pasture is unavailable and/or hay is limited, needs could require a high quality grass hay at 1 percent of her body weight in combination with as much as 6 to 7 pounds of a typically formulated grain mix daily.

Grain needs for mares on pasture will vary widely due to quality and quantity of available forage. It is important to observe grouped mares individually as those in low body condition may need to be removed from the herd and fed supplemental grain. It is important to remember that mares in a marginal or thin condition can quickly lose condition when moved to the new surroundings and activities of a breeding farm. Increasing body condition on these mares prior to moving to the breeding farm will help avoid delays in the onset of estrous and conception.

Protein needs.

The open mare’s protein requirements are no different than those for other mature horses at similar weights. A 1,200-pound mare will need about 1.5 pounds of crude protein per day. This relates to feeding 15 pounds of a 10 percent crude protein ration. One must consider both hay and grain sources of protein when determining fed levels, so it is good practice to have the hay source analyzed for protein. For example, if 11 pounds of bermudagrass hay analyzed to be 10 percent crude protein is fed with 6 pounds of a 12 percent crude protein grain mix, one would be feeding about 1.8 pounds of crude protein. Usually, protein requirements are met when feeding adequate grain to maintain energy levels for a fleshy condition in mature, open mares.

Calcium and Phosphorus Needs.

Calcium and phosphorus are the major minerals of concern. Calcium and phosphorus requirements of open mares are dependent on the body weight and digestibility of minerals in the feed. A 1,200-pound mare will need about 22 grams of calcium and 15 grams of phosphorus per day. This level relates to feeding a grain-hay ration with .3 to .4 percent calcium and .15 to .2 percent phosphorus. Calcium levels should be 1.5 to 2 greater than phosphorus levels in the total ration. Hays are usually higher in calcium than phosphorus, but levels of available minerals will vary greatly from different hay crops. Most commercial grain mixes contain equal amounts of calcium and phosphorus to ensure a proper ratio. Grain mixes should contain a minimum of .5 percent calcium and .4 percent phosphorus when combined with grass hays to ensure adequate amounts of these minerals.

Vitamin Needs.

Vitamin requirements are generally met in open mares when feeding high quality grain and hay. Most commercially available grain mixes have added vitamin sources to ensure adequate vitamin levels. Vitamin premixes can be fed to supplement questionable feed sources but should be fed only at recommended Ievels.

Mares in Last 90 Days of Gestation

The mare in late gestation differs nutritionally from the open mare. Her nutrient requirements are slightly higher because she is maintaining her body and supplying nutrients to a rapidly growing fetus.

Body Condition and Energy Needs.

The mare requires an additional 3 to 4 megacalories of digestible energy above maintenance requirements. This increased energy need can be met by feeding more of the same grain mix she was consuming when open and during early gestation. A 1,200-pound mare will need about 2 to 3 pounds of additional grain mix per day when she enters late gestation to meet her increased energy requirement. It is important that she remain in fleshy condition if she is to be rebred following foaling. The added nutritional stress brought on by early lactation can cause mares in a marginal condition to drop in condition to the point of affecting rebreeding efficiency. Also, many pastures are in their lowest nutritive value this time of year. Close inspection of mare condition is necessary so grain and hay levels can be adjusted accordingly.

Protein Needs.

The gestating mare has a slightly increased need for protein above her requirement in the open state. Crude protein requirements will increase about 1/2 of a pound when mares are in late gestation. This increased need above maintenance is usually met when feeding more grain mix to supply adequate energy, so a higher percent protein grain mix is usually not necessary.

Calcium and Phosphorus Needs.

As with other nutrients, the amount of calcium and phosphorus required during late gestation is increased above the amounts needed in the open state. These mares require approximately 20 more grams of calcium and phosphorus than when in an open state. As with protein, these amounts are usually more than adequately met when increasing the amount of grain mix for energy purposes.

Vitamin Needs.

The major vitamin of concern during late gestation is vitamin A. Vitamin A requirements are doubled when mares are in late gestation and lactation. Most commercially prepared grain mixes have sufficient levels of added vitamin A to adequately meet requirements; however, many producers routinely feed a vitamin premix to gestating mares consuming feeds of questionable vitamin levels. It is important that the premix contain about a 9 to 1 ratio of Vitamin A to Vitamin D, a 6 to 1 ratio of Vitamin D to Vitamin E and be fed at levels recommended on the label. Overfeeding of several of the vitamins can cause irreversible damage to the mare and fetus.

The Lactating Mare

The wet mare’s nutrient requirements are greatly influenced by the amount of milk produced to supply the nutrient needs of the foal. Milk yields range from two to three percent of the mare’s body weight per day, so it can be easily seen that nutrient needs are greatly increased.

Body Condition and Energy Needs.

Energy requirements will nearly double following foaling. It is usual for a 1,200-pound mare to need 12 to 15 pounds of an average energy density grain mix in addition to 10 to 12 pounds of a good quality hay to meet her energy needs. Careful management is necessary in this class of mares because individual requirements will vary greatly. A foal can quickly lower condition in the mare, and wet mares in a thin body condition may take longer to rebreed and have lower pregnancy rates than mares in a moderate to fleshy condition. Also, the mare may be moved to a new location for breeding soon after foaling, which can create a loss in condition due to stress. It is extremely difficult to increase condition in lactating mares because the amount of feed that would be necessary can lead to higher incidence of founder and colic. As such, it is important that the mare is adequately conditioned before foaling.

Protein Needs.

Protein requirements are also important during lactation because of the large amounts of protein leaving the mare in the milk. Mares not receiving adequate protein have decreased milk production, resulting in lowered foal growth. Requirements double in heavily lactating mares, and an increased percent protein ration is usually necessary. Most hay-grain combinations dictate that the grain mix be at least 14 percent crude protein. Grain mixes with 10 to 12 percent crude protein should be fed with a hay high in crude protein, so many producers feed a high quality alfalfa with this type of grain mix.

Calcium and Phosphorus Needs.

Calcium and phosphorus needs will also double in the lactating mare as compared with her requirements for maintenance. The calcium and phosphorus density of the grain ration will depend on the amount of grain and hay that is fed. The mineral density of most rations should be increased to levels of 0.6 percent calcium and 0.4 percent phosphorus to meet the added requirement. Mineral needs can be met when increasing the amount of grain mix fed for energy needs. If grain and hay sources are marginal in their mineral densities, it is advisable to add a mineral premix to rations for this class of mare. Mineral premixes, like vitamin premixes, should be added only at recommended levels.

Vitamin Needs.

Most classes of horses will meet their vitamin needs if they are fed high quality grains and hays. Vitamin requirements increase in lactation to the point that it is a good practice to add a vitamin source to grain mixes. Feed suppliers and feed tags should provide information on whether grain mixes have been fortified with vitamins during the feed manufacturing process. If not, it is recommended to add a vitamin supplement on-site to the grain mixes for lactating mares. Vitamin premixes should contain about a 9 to 1 ratio of Vitamin A to Vitamin D, and about a 3 to 1 ratio of Vitamin D to Vitamin E and be fed at levels recommended from label directions to ensure proper levels of these vitamins.

David W. Freeman, OSU Extension Equine Specialist, OSU Department of Animal Science; Lyndi Gilliam, DVM, DACVIMEquine Internal Medicine Veterinarian, OSU Center for Veterinary Health Sciences

Poor body condition in horses can be caused by many factors. Age, disease and lack of adequate nutrition are three of the most common. Usually, nutrition-related reasons are due to a lack of carbohydrate, fat or protein intake. However, even with appropriate care and nutrition, elderly horses may not be able to maintain a desired body condition. Similarly, numerous diseases can lead to poor body condition, from a lack of appetite, or the inability of the horse’s body to function normally.

A refeeding plan coordinates nutritional and veterinary therapies that combine to improve body condition of the horse. Successfully refeeding a horse in poor condition can be extremely difficult, even with knowledgeable supervision and a detailed, well-referenced plan. One veterinary science study reported that nine of 45 horses that had previously been subjected to prolonged malnutrition died after being placed with a responsible caregiver who provided an appropriate diet. Defining a refeeding plan requires in-depth diagnosis of the health status of the horse. Veterinarian intervention, therefore, is necessary prior to and during the refeeding period of poorly conditioned horses. Typically, veterinarians will perform physical examinations that include a detailed dental exam and subsequent diagnostic tests to evaluate concerns noted during physical examinations.

Assessing Body Condition

Body condition relates to the amount of visible fat cover on a horse’s body. The most commonly accepted assessment method is a scoring system using a scale of 1 to 92. A thorough explanation of the scoring system is discussed in OSU Extension Fact Sheet F-3920 Body Condition of Horses. Figure 1 defines the locations on a horse’s body that have observable differences of fat cover at different body conditions. Horses in the low end of the condition scale have little noticeable fat cover at locations along the neck, behind the withers, along the ribs and on the hip. The individual bony structures of vertebra and the pelvis are noticeable (Photos 1 and 2).

Picture 1. Horse in a body condition score 1. Note skeletal features evident in areas of normal fat deposition. Photo courtesy of Dr. Don Henneke, Tarleton State University.

Picture 2. Horse in body condition score of 2. Note the evidence of individual vertebra along the back and croup area.

Horses in poor to very thin body conditions (Scores of 1 or 2) have little visible fat and appear to have had appreciable horse lean tissue degradation. Body fat provides the major energy reservoir. The horse’s body systems will mobilize fat for fuel when energy needs are greater than the daily energy intake. As the time period of inadequate nutrition is prolonged, fat stores are depleted and noticeable amounts of muscle are broken down for use as energy.

There is no uniformly agreed upon benchmark as to what constitutes a horse in undesirably low body condition. It is common for some highly trained equine athletes to have thin to moderately thin body conditions and be in the peak of health. Generally, most reports from veterinarians and nutritionists consider horses in body condition scores of one or two as emaciated, malnourished or under-conditioned as a result of being underfed, combating a disease or having an age-related condition that restricts weight gain.

Poor body condition is usually associated with insufficient intake of energy or protein. Malabsorption, parasitic infestation, old age, senility and a number of diseases can also cause emaciation. Thus, to be effective, nutritional therapies for correcting poor body condition must be aligned with the correct diagnosis of the cause and the health status of the horse.

Review of Published Reports on Refeeding Poor Conditioned Horses

Some horses with poor body condition may be so dehabilitated that they are unable or lack the desire to eat. Horses in this condition will require veterinary intervention. A feeding tube can be placed into a horse’s stomach so a liquid diet can be administered if a horse is unable or unwilling to eat. Placing a nasogastric tube into a horse’s stomach should be performed by a veterinarian as an improperly placed tube can result in death. An intravenous catheter can supply nutritional support if a horse’s digestive tract cannot handle liquid or solid food. This type of nutrition is costly and is only used short term until the digestive tract will accept and utilize feed.

The feeding frequency, dietary nutrient profile and physical form of the diet will define the refeeding plan. Although limited in both number and scope, there are reports in veterinary and nutritional science journals that provide guidance for refeeding plans. The rations recommended in specific reports likely are influenced by the availability of specific feeds and processing methods at the time and location of the report, regional traditions of what routinely is fed and personal experience. As such, the specific ingredients mentioned may not be as important as are similarities of nutrient composition and routines among the reports.

In general, it is recommended to provide grain following one or two days after feeding long-stem forage. Grains are relatively high in starchy carbohydrates, and there is some concern among veterinarians and nutritionists that horses in poor condition may not utilize these ingredients initially with as much success as high-fiber feedstuffs. Recommendations are to begin refeeding by starting with water, electrolytes, and in most cases, hay, followed with frequent meals of small amounts of grain 3,4,5.

One suggested protocol is to begin with offerings of small amounts of hay, that is,2 pounds every two hours. After several meals, amounts are increased to levels approximating about one-half the needs for dietary energy for maintenance by feeding hay in four meals per day for two days. Hay is then offered free choice.

This diet should continue for a couple of weeks, after which additional nutrient sources such as grains are introduced. Similar to hay, grains should be introduced gradually by initially feeding small amounts at frequent intervals.

One such recommendation is to introduce grain by apportioning into five to six daily feedings of 1 pound to 1.5 pounds each. This level should be tolerated well by most averaged sized stock horses. Even so, recommendations emphasized the need to treat horses individually and adjust rationing frequency and levels according to the horse’s response.

A different report provides another routine for introduction of a grain mix. Horses in extremely poor condition are to be offered hay and water if they are initially unable to walk, along with initial diets prescribed by a veterinarian. Once they are stabilized, a 12 percent crude protein grain mix with mineral supplement, molasses and bran is prescribed to be fed three times daily at levels of about 1 pound per feeding. After one week, the levels are increased to 2 pounds per feeding for the a.m. and p.m. feedings, with the noon feeding remaining at 1 pound. Once the horse's condition has improved somewhat, the grain mix is to be fed at levels of 3 to 9 pounds per day, depending on the size of the horse. The horse continues to receive free choice levels of hay and unlimited access to grazing. After 30 days of feeding, zero to 16 pounds of the grain mix is fed daily into two allotments each day. The estimated time period to improve body condition from a very poor condition to a moderate condition is six to 10 months.

A 2004 report from the College of Veterinary Medicine at the University of Minnesota provides a refeeding protocol based on their college's experiences of treating poorly conditioned horses. A systematic protocol is outlined that includes monitoring of weight, physical examinations, parasite treatment and blood chemistry profiles. The dietary protocol begins with restricted intake of high quality grass hay. Hay is offered by hand at hourly intervals for the first day if horses had no oral intake for the previous 24 hours. If the horse had some feed before admission, it was permitted full access to grass hay. A complete feed is gradually introduced beginning on the fourth day at 1/2 pound per meal, twice daily for an average size horse. A complete feed is formulated to contain all nutrients needed in the diet of a horse in a processed mix and does not require the addition of hay for balancing nutrient needs. The amount or frequency of feeding the complete feed is increased gradually every other day to a maximum of 3 pounds per feeding as long as the horses are consuming the allotted amount. Trace minerals are added in block or loose form beginning on the fourth day.

Twelve horses receiving this protocol reported weight gain that varied greatly, from horses showing little to no gain to some gaining as much as 6 to 7 pounds per day for 11 days. These high levels of gain per day are likely to be reflective of body-fill of forage and water in the digestive tract. Rates of gain of actual tissue may be more in the range of 1 to 3 pounds of gain per day during the initial refeeding period. Body condition scores averaged a score of 2 with a range of 1 to 3. Body weights ranged from approximately 400 to 1,100 pounds and ages from 5 months to over 20 years.

Most reports, as those above, have made recommendations based on clinical experience and review of case studies instead of controlled research studies that accurately quantify the response of undernourished horses to different diets. One trial that has conducted such research has been reported by investigators at the School of Veterinary Medicine at University of California, Davis7. Twenty-two poorly conditioned horses were divided into three groups. The previous histories of the horses were unknown. On average, the horses weighed about 700 pounds, between 14 and 15 hands tall and in a body score of 1 or 2.

The groups differed in the type of diet: alfalfa hay, oat hay or a third diet made of a combination of oat hay with a commercially available, complete feed containing grain and high-fiber components. The horse’s physiological response to the initial 10 days of refeeding were observed and compared.

The three different diets were fed at equal levels of energy intake. For the first three days, the horses were fed six times per day at levels estimated to provide 50 percent of their normal digestible energy requirements. This equated daily to 6 to 7 pounds of alfalfa hay, about 9 pounds of oat hay or s7 pounds of the oat hay with the complete feed. Amounts were increased to estimated levels of 75 percent of their normal digestible energy requirements for the following two days, and then increased to 100 percent of their estimated digestible energy requirements for the last five days of the investigation. The number of meals fed was reduced from six to four times per day during days six through 10. Total intake on day 10 averaged about 13 pounds of alfalfa, 17 pounds of oat hay or 13 pounds of the oat hay-complete feed mix.

Weight gains were not different between the three groups of horses, although alfalfa hay was suggested to have several advantages. The oat hay was very bulky and caused diarrhea in several horses, and the oat hay was lower in some essential minerals. The authors cautioned against the initial use of the higher starch-containing ration of the oat hay combined with a complete feed because of evidence suggesting the potential for adverse blood insulin responses. An undesirable insulin response to the initial period of refeeding is one of the noted concerns with researchers studying the effects of reintroducing food following prolonged malnutrition.

The same researchers subsequently compared alfalfa hay with an alfalfa hay combined with corn oil. The addition of corn oil reduced the amount of hay needed to be fed at comparable estimated digestible energy intakes. While the addition of corn oil had no harmful effects, the investigators still recommended the alfalfa hay without corn oil. More hay was fed without the addition of corn oil, which increased the intake of minerals contained in the hay.

Regardless of diet composition, the researchers emphasized the need for small, frequent allotments of food being offered in the initial refeeding period. They recommended that horses can be fed as much as they will eat of an alfalfa hay diet after 10 days to two weeks. Although some weight gain can be expected after one month of care, they suggested that three to five months will be necessary for the horses to return to normal body weight.

Suggested Feeding Plans for Reconditioning Horses in Poor Condition

Several recommendations for the initial refeeding of horses in poor condition can be developed from the suggestions and research discussed above. A physical examination, including careful examination of the oral cavity and appropriate diagnostic tests, should be performed by a veterinarian so nutritional plans can be aligned with the health status of the horse. It is possible that appetite or ability to eat solid feed may be compromised. In that case, supportive liquid diets may be prescribed by a consulting veterinarian.

Water should be offered and intake documented. The most common course is to feed hay or coarsely processed forage for the first several days. Forage should be of high quality, and alfalfa is recommended as one suitably desired forage type. If hay is not available, alfalfa cubes may be an alternative. Softening cubes by soaking in water may be necessary if the horse’s dental condition is poor. Indigestible, bulky, poor quality forage is not recommended because of its poor digestibility and lower levels of nutrients.

High quality pastures can be used as the initial source of nutrition. Intake patterns should be observed to ensure horses are eating. Restricting horses to limited grazing may be necessary on pastures with moderate to lush vegetation. In these situations, turning horses to pasture three to four times a day for one or two hours is a logical starting point.

Grains can be introduced into the feeding program after using forage for the first several days. By doing so, horses are consuming most of the intake of carbohydrate as fiber rather than starch. However, note that not all processed feeds are high in starch. Soyhull pellets, alfalfa meal pellets or other high-fiber byproducts may be a logical alternative to long-stem forage if lower starch, higher fiber rations are desired.

Grains will provide a more concentrated source of useable energy as compared to a high-fiber feed because starch will be more digestible than fiber. As such, it is advantageous to introduce grains soon after the initial refeeding period of one to four days. Grains should be fed in several small meals per day and amounts gradually increased to levels typical of horses of similar size and weight when in moderate condition. Feeding amounts for a 900- to 1,000-pound horse can start at 1 to 2 pounds of grain per day for the first two to four days, and increased to twice that amount by seven to ten days. Feeding frequency of grain can be reduced to two to three times per day sometime during the second week of feeding. Horses should be monitored closely for signs of laminitis or founder. These conditions are evidenced by reluctance to move, by walking very gingerly or tenderly, and by increased time spent lying down or rocking back on the hind legs before moving the front legs. A veterinarian should be contacted immediately when any of these signs are observed.

There are differences in the nutrient content of commercially prepared concentrate feeds. Some mixes have large amounts of fiber added to a grain and are labeled as complete feeds. These mixes can substitute the need for forage more so than mixes containing larger amounts of higher starch-containing ingredients. These feeds will usually have increased fat levels by inclusion of plant oil to the mix. Supplying supplemental oil as part of the processed mix, or supplementing grain mixes and pelleted high-fiber feeds by topdressing an oil, has the advantage of increasing the energy density of the feed. Vegetable oil contains much more energy per weight as compared with high carbohydrate, low-fat feeds.

There is little information as to determining the need for increasing levels of protein above amounts normally recommended to be fed to horses of similar size. However, protein tissue may have been broken down, thus requiring a need for protein growth during refeeding. As such, it is logical to suggest protein requirements are increased to represent levels more characteristic of younger horses in similar growth. Increasing the suggested requirement for crude protein by about 20 percent above normal maintenance levels may better meet needs during initial refeeding of poorly conditioned horses. As an example, a 1,000-pound horse may require approximately 1.25 pounds of crude protein in maintenance conditions. When refeeding a horse in poor condition of similar size, requirements for crude protein may increase to 1.5 pounds of crude protein per day. To determine the protein intake of a horse, the amount of ration by weight is multiplied by the percent crude protein of the ration. For example, a horse consuming an all-alfalfa hay ration, which is 20 percent crude protein at levels of 10 pounds per day, would be consuming 2 pounds of crude protein.

Similar adjustments to minerals and vitamins could be assumed for similar reasons when refeeding a poorly conditioned horse. As such, grains and complete feeds formulated for horses in growth may have advantages of use for refeeding as compared to formulations with fewer nutrients per pound intended for horses at maintenance.

Total intake of feed will be limited to the horse’s level of appetite and the maximum voluntary intake. In most situations, horses will voluntarily consume as much as 3 percent of body weight per day in diet dry matter. While the dry matter of pasture can vary greatly, most grains and hays are about 90 percent dry matter. For example, a 1,000-pound horse may be expected to consume as much as 30 to 35 pounds of hay per day voluntarily. In some situations, the appetite of the horse will restrict voluntary intake to levels much lower than normal when the horse is in poor condition. Also, a grain mix will likely be combined with hay when refeeding poorly conditioned horses. The addition of a higher energy feed will decrease the need to feed rations at maximum levels of voluntary intake.

Accurately assessing improvement is important. Initial body weight and weight gain should be recorded. Weigh tapes can be used if large animal scales are unavailable. Weight gain is expected to be highly variable between horses. Initial weight gains of 1 to 2 pounds per day would be expected for favorably responding horses with a body weight between 900 and 1,000 pounds. Significant weight gains sufficient to change body condition score will take a minimum of several weeks. Also, veterinarian assessment of health should be routinely scheduled as part of the refeeding plan. Related health factors, degree of emaciation and the horse’s response to refeeding will direct the refeeding plan, so use the suggestions as a general guide.

Body Condition Scores

1 Poor. Animal extremely emaciated. Spinous processes (portion of the vertebra of the backbone which project upward), ribs, tailhead, and bony protrusions of the pelvic girdle (hooks and pins) projecting prominently. Bone structure of withers, shoulders and neck are easily noticeable. No fatty tissues can be felt.

2 Very Thin. Animal emaciated. Slight fat covering over base of spinous processes and transverse processes (portion of vertebrae which project outward) of lumbar (loin area) vertebrae feel rounded. Spinous processes, ribs, shoulders and neck structures are faintly discernable.

3 Thin. Fat built up about halfway on spinous processes, transverse processes cannot be felt. Slight fat cover over ribs. Spinous processes and ribs are easily discernable. Tailhead prominent, but individual vertebrae cannot be visually identified. Hook bones (protrusion of pelvic girdle appearing in upper, forward part of the hip) appear rounded but are easily discernable. Pin bones (bony projections of pelvic girdle located toward rear, mid-section of the hip) not distinguishable. Withers, shoulders and neck accentuated.

4 Moderately Thin. Negative crease along back (spinous processes of vertebrae protrude slightly above surrounding tissue). Faint outline of ribs discernable. Tailhead prominence depends on conformation; fat can be felt around it. Hook bones are not discernable. Withers, shoulders and neck are not obviously thin.

5 Moderate. Back level. Ribs cannot be visually distinguished but can be easily felt. Fat around tailhead beginning to feel spongy. Withers appear rounded over spinous processes. Shoulders and neck blend smoothly into body.

6 Moderate to Fleshy. May have slight crease down back. Fat over ribs feels spongy. Fat round tailhead feels soft. Fat beginning to be deposited along the sides of the withers, behind the shoulders and along sides of neck.

7 Fleshy. May have crease down back. Individual ribs can be felt, but noticeable filling between ribs with fat. Fat around tailhead is soft. Fat deposited along withers, behind shoulders and along neck.

8 Fat. Crease down back. Difficult to feel ribs. Fat around tailhead very soft. Area along withers filled with fat. Area behind shoulder filled in flush. Noticeable thickening of neck. Fat deposited along inner buttocks.

9 Extremely fat. Obvious crease down back. Patchy fat appearing over ribs. Bulging fat around tailhead, along withers, behind shoulders and along neck. Fat along inner buttocks may rub together. Flank filled in flush.

For more information on body condition scoring, visit the Body Condition Scoring Learning Module.

David W. Freeman, OSU Extension Equine Specialist

Introduction

Horses are fed a variety of forms and types of feeds. Diets range from 100 percent pasture forage to 100 percent completely processed mixes. Most horses are fed forage in the form of hay or pasture in combination with a grain mix. The choice of feed is influenced by the horses’ requirements, availability of pasture, availability and cost of commercially prepared feeds, what traditionally has been fed, and how the horses are used and managed.

Nutrients should be supplied in the amount, form and method that safely and efficiently meet requirements. Correctly supplying nutrients to horses requires knowledge of requirements, feeds and nutritional management.

Most horse owners rely on formulated feeds from commercial sources, or on a nutritionist’s support for customer formula mixes. Even so, in order to make accurate decisions, horse owners should have a general knowledge of nutrients, how nutrient needs change with different production and use classes of horses, and how to determine if nutrient supply is aligned with requirements. This fact sheet provides information on the nutrient needs of horses and how these needs change with age and production status.

Nutrient Needs

The basic classes of nutrients are energy, protein, minerals, vitamins and water.

Energy

Energy is not a nutrient in the sense of an identifiable substance; rather it is utilized as fuel for body processes and is released when energy-containing substances are broken down by the horse’s body. A calorie is a unit of energy that represents a standard amount of heat released when an organic compound is broken down. Calorie with a capital C is the unit used in human food literature. A Calorie is a kilocalorie which is 1,000 calories. Energy requirements for horses are expressed as digestible energy needs per day in Megacalories, which is 1 million calories, or 1,000 Calories (kilocalories).

Digestible energy is the portion of the energy fed, gross energy that is absorbed from the digestive tract (Diagram 1). In order to accurately determine the digestible energy value of a ration, gross energy and energy remaining in the manure would have to be determined experimentally. Feed laboratories and nutrition tables use estimates for digestible energy based on the levels and types of energy-containing substances in a particular feedstuff.

The energy-containing substances in feeds are carbohydrates, fats and protein. Carbohydrates are the largest suppliers of energy. There are two general types of carbohydrates based on chemical structure, which in turn, affects how the types are digested by the horse.

The two types of carbohydrates are fibrous and nonfibrous carbohydrates. Each type contains a variety of compounds that vary in digestibility. Fibrous carbohydrates provide structure to plants. Large amounts are found in seed coats of grains and stems of plants. Horses do not secrete enzymes that break down fibrous carbohydrates; rather, fibrous carbohydrates are digested by bacteria and protozoa in the horse’s digestive tract. Portions of the products of this microbial digestion are absorbed by the horse and used for energy. These microbes are located mainly in the cecum and large intestine, which are components of the digestive tract located after the stomach and small intestine (Figure 1.).

Hemicellulose and cellulose are the main types of fibrous carbohydrates in horse diets. Fiber digestibility will decrease as the amount of cellulose increases, as compared with hemicellulose and some of the other smaller fibrous compounds. The presence of lignin, an indigestible compound found in large amounts in woody plants, is especially important. Lignin is not digested by the horse’s enzymes or microbes in the digestive tract. Further, complexes with cellulose are formed that decrease the digestibility of cellulose as the amount of lignin increases. The relative amount of cellulose and lignin increases when plants mature, so mature plants are not as digestible as immature plants.

The relative amounts of fibrous carbohydrates also vary between plant types and parts of the plant. Plants with large stems and few leaves will be less digestible because of larger amounts of indigestible fiber. Pasture plants and hay generally have more fibrous carbohydrates than levels found in the harvested grains. Grains will have large amounts of nonfibrous carbohydrates as compared to levels found in most grazed or harvested forages.

The nonfibrous carbohydrates are mainly starches and sugars. Analyses for nonfibrous and nonstructural carbohydrates account for much of the same types of carbohydrates. Plants have larger levels of nonstructural carbohydrates when immature and growing. Seeds of plants (grains) have relatively large amounts of nonstructural carbohydrates as compared with stems and leaves. Different plants and grains vary in the levels of these carbohydrates. For example, corn and wheat typically will have more starches and sugars compared to oats.

Nonfibrous carbohydrates are more digestible than fibrous carbohydrates, as nonfibrous carbohydrates are partially broken down by enzymes secreted by the horse and absorbed in the small intestine. Nonfibrous carbohydrates not absorbed in the small intestine are digested by microbes in the cecum and large intestine, and portions of the products of this microbial digestion are absorbed for energy use.

More nonfibrous carbohydrates will pass to the cecum and large intestine as larger amounts are fed in a single meal. Microbes in the cecum and large intestine readily digest nonfibrous carbohydrates. Too much microbial digestion of these compounds occurring too quickly causes a build up of substances that alter the normal state of the horse’s digestive tract. These changes can lead to laminitis and colic.

Because of this, the amounts of nonfibrous carbohydrates fed as a meal should be regulated. Horses introduced to pastures with large quantities of immature, growing forage should be limit grazed. Grains should be limited at or below levels of about 0.5 percent of body weight per meal, that is, 6 pounds of a grain mix or less per meal for a 1,200-pound horse. Grain mixes should be split into several meals per day when larger amounts of nonfibrous carbohydrates are fed (See Extension Fact Sheet NSC-3973 “Feeding Management of the Equine”).

Fats are a group of chemical compounds (fats, oils and waxes) that contain fatty acids. Some of the fatty acids are essential, meaning they are needed but not produced by the body itself. The breakdown of fat produces about twice the energy as compared to similar amounts of carbohydrates or protein. Feeds have smaller amounts of fat than carbohydrates or protein. Some of the grain byproducts used for feed will have larger percentages of fat because carbohydrates are removed during the milling of the grain. Fat amounts of feeds are increased by using certain byproducts or by adding vegetable oil to mixes.

The body also breaks down dietary protein for energy use. However, energy production is more efficient when there are enough carbohydrate and fat compounds to produce the majority of energy needs. The main purpose of dietary protein is supplying amino acids rather than energy.

Mature horses of larger weight require more energy to maintain their body than do smaller horses. Working horses will need more energy than horses not receiving forced exercise. Mares producing foals, lactating mares and growing horses will need large amounts of energy to fuel their production of body tissue. Similarly, energy needs are larger when energy use is increased to provide warmth during cold environmental temperature -- normally below 30 to 40 degrees F if horses are adapted to the cold.

Energy intake above the amount needed to fuel the body for maintenance, production and growth processes will be deposited as fat (See Extension Fact Sheet ANSC-3920 “Body Condition of Horses”). Horses in good body condition receiving insufficient daily energy intake will burn energy that is stored as fat. Horses in poor body condition receiving insufficient daily energy intake will decrease in body weight and body condition and over time will develop serious health problems that may lead to death.

Protein

Protein is made of amino acids, and horses actually have an amino acid requirement rather than a requirement for protein. Amino acids are needed to maintain and produce muscle, enzymes and hormones, and play key roles in many different body processes. Part of the protein in feed is digested by enzymes in the small intestine and absorbed as smaller units containing the dietary amino acids. Otherwise, the protein is broken down by microbes in the cecum and large intestine beyond the amino acid level, or leaves the body undigested.

Some of the amino acids must be supplied in the diet because the horse’s body cannot make them. These are collectively termed as essential amino acids. Lysine is the most limiting amino acid for growth as it is an essential amino acid and is needed in relatively large amounts. Feeds containing relatively large amounts of essential amino acids are considered to be higher quality protein sources because essential amino acid levels align more closely with needs. Feeds vary in the amount of protein and the relative distribution of amino acids of the protein. For example, soybean meal contains more lysine than cottonseed meal. To ensure a good balance of amino acids, the minimum level of lysine should be at or above 4 percent of the total crude protein intake, especially for growing horse diets.

Protein needs are expressed as crude protein which is the amount in the ration. Like all nutrients, protein must be digested to be usable. Generally, protein in grain and grain byproducts is more digestible than protein in forages. Horses need a certain amount of protein per day for maintenance of their body. As with energy, states of production and growth will increase protein requirements.

Increased protein needs can be met by feeding more of a diet without changing the percent protein concentration of the diet. Other situations will require diets with greater protein density (crude protein percentage) to meet the larger demands. Generally, diets of growing and lactating horses will be formulated to contain a higher crude protein percentage, as compared to diets formulated for other horses. Although losses of protein increase with increased sweat loss during exercise, protein density of diets for mature, exercising horses does not necessarily require increasing the protein densities above that in maintenance diets. Increased requirements for protein during exercise can be met when amounts of the maintenance ration are increased to meet the added energy to meet requirements. Similarly, the increase in protein needs for pregnancy may be met when more of the maintenance diet is fed to meet weight gain needs in late gestation.

Minerals

Minerals are inorganic compounds needed as components of body tissue and as facilitators of various body processes. The two minerals of largest requirements are calcium and phosphorus, especially when tissues that contain large amounts are actively growing. Thus, relatively large amounts of calcium and phosphorus are required in the diet of growing horses that are building bone. The total dietary supply of minerals should contain more calcium than phosphorus as needs for calcium are greater than phosphorus, and large amounts of phosphorus can interfere with calcium absorption. Diets are recommended to contain about 1.5 to 2.5 times more calcium than phosphorus.

Other minerals with established requirements include sodium, potassium, zinc and copper. Salt, sodium chloride, is a normal addition to grain mixes at about the 0.5 percent level and supplied free choice in the form of blocks. Some sources of salt contain trace minerals, which are several different minerals needed in trace amounts. The need for copper and zinc is much less than needs for calcium or phosphorus; however, these are two additional minerals routinely balanced for in rations, especially for diets formulated for growing horses.

Many of the minerals needed in small amounts do not have well established requirement levels. Many of the minerals have a wide range of dietary concentration acceptability as increases in intake above what is actually needed are easily expelled from the body. Others may be toxic at high levels, so care must be taken to account for all sources of minerals before large amounts of mineral supplements are fed. Commercially prepared feed mixes may include added minerals, so additional sources are not needed. On-farm topdressing of mineral supplements should account for levels in feed. Using a single source of mineral supplement instead of multiple sources will guard against oversupply. With the exception of salt, voluntary mineral intake is not highly correlated with the actual mineral needs of horses. As such, minerals are best provided as part of a formulated mix. The ability of free choice mineral supplements to provide minerals in amounts needed depends on the formulation of the mineral supplements and the intake patterns of horses.

Vitamins

Vitamins are organic compounds needed in trace amounts that regulate a multitude of bodily functions. There are two general classes of vitamins: fat soluble and water soluble. Fat soluble vitamins are absorbed with fat, water soluble absorbed with water. The main fat soluble vitamins are vitamins A, D, E and K. The water soluble vitamins are the B vitamins and vitamin C.

Most, if not all the vitamin needs of horses are supplied by levels naturally occurring in grains and forages. Green forages are good sources of vitamins A and E. While most if not all of the horse’s maintenance requirement for vitamin A is met by a compound present in forages, vitamin A needs such an increase in production and growth that supplementation may be necessary. Needs for vitamin A are the largest, followed by Vitamins D and E. Given access to sunshine and exercise, most horses will not need Vitamin D supplementation unless they are rapidly growing or preparing for heavy exercise at young ages. The B vitamins are thought to be produced in sufficient amounts to supply the needs of most horses, although it is recommended frequently to supplement rations used for horses being heavily worked.

Commercially prepared horse feeds routinely supplement fat soluble and water soluble vitamins at levels above suggested requirements, so the need for on-site supplementation is not necessary. Excess intake of fat-soluble vitamins A and D is detrimental since fats and the substances soluble in them are poorly excreted from the body. Excessive intake of water-soluble vitamins is rarely detrimental, as water-soluble substances are readily excreted from the body. Feed vitamin premixes only at levels recommended on the label and account for sources added to grain mixes before deciding to topdress.

Water

Water is not often thought of as a nutrient, although lack of water intake causes illness and death much more quickly than lack of feed nutrients. Water requirements vary with losses, so horses housed in hot environments or those losing large amounts through sweat, respiration or milk will need more water than nonproducing or sedentary horses. Intake is expected to be larger in hot environments, with larger feed intake or larger horses.

With the possible exception of the extremely hot horse immediately following hard exercise, water should be offered free choice as the bigger concern is lack of intake. Extra intake of water is easily expelled via urine. Voluntary water intake is expected to vary considerably between horses and by the same horse on different days. Water consumption should be monitored whenever possible so normal intake levels can be assured and observed. Sources that supply fresh, clean water supply are preferred as contaminants may decrease voluntary intake or contain products harmful to the health of the horse.

Estimates for Nutrient Requirements

The National Research Council of the National Academies provides documents on nutrient requirements of animals. The estimates provided in the tables in this Fact Sheet are based on recommendations from the National Research Council. Tables 1 through 5 display how nutrient requirements are expected to change with differences in body size or production. The tables display estimates for requirements of digestible energy, crude protein, and several minerals and vitamins.

Nutrient requirements are estimated from the National Research Council’s Recommendations for Nutrient Requirements of Horses (2007). Mcal is megacalories (1,000 Calories), a unit of energy potential.

a) Nutrient requirements are estimated from the National Research Council’s Recommendations for Nutrient Requirements of Horses (2007). b)These levels take into account all sources of minerals in the diet including hay, grains and supplements.c)Different sources of minerals will have differing concentrations of minerals so accounting for ingredients and reading labels is important.

a) Nutrient requirements are estimated from the National Research Council’s Recommendations for Nutrient Requirements of Horses (2007). b) These levels take into account all sources of vitamins in the diet including hay, grains and supplements. b) Different sources of vitamins will have differing concentrations of vitamins so accounting for ingredients and reading labels is important.