An important test to be sure your foal is well protected against disease is an IgG test. This test will make sure the foal received adequate antibodies from the mares milk. An IgG test on the foal 16 hours after he first nursed would seem prudent to me. IgG is shorthand for the type of immunoglobulin the foal receives from the mares colostrum. An immunoglobulin is a protein that is produced by the cells of the immune system that circulates in the blood and provides defense against infectious diseases and toxins. So, if everything goes well, the mare secretes her own IgG into the colostrum or first milk to the foal.
IgG is a rather large protein molecule that would normally be digested in the stomach and small bowel and there fore lose its ability to fight infections. However for about the first 12 hours after birth, the bowl is receptive to these large protein molecules and will absorb them intact. This process of production, secretion, ingestion, and absorption, is called passive transfer.
Some problems that may prevent passive transfer are: 1. No colostrum 2. Low levels of IgG in the colostrum 3. Foal does not nurse well 4. Foal does not absorb the proteins well So you can see there are all types of reason for failure. There are a number of ways to check to see if the process is working.
The colostrum can be checked for immunoglobulin content by checking it’s specific gravity with a hydrometer. Specific gravities greater than 10.60 are considered good and tends to be sticky between the fingers.
A better way to check for adequate passive transfer is by running a check on the foal’s blood at 16 hours after the foal has first nursed. There are very accurate, easy to read tests for this that the vet can run on the serum. The problem is interpretation of the results. We know the foal with less than 200 mg/dl IgG in it’s blood is going to have problems. In the past 400 mg/dl has been considered the low end of acceptable. However in the 200 to 400 range a lot of controversy appears. It is best to consider the IgG level in light of the total picture. The 200 to 400 range might be OK if the foal and mare are healthy and the environment optimal. On the other hand levels below 800 (yes 800!) is not acceptable in the foal who is already sick. The foal uses up and breaks down the mare IgG. We know infection rapidly diminishes the IgG levels.
Should every foal be checked? Remember, once a foal develops a systemic infection they are very difficult and expensive to treat. These tend to be mixed, resistant, toxin producing, gram negative blood infections. On the other hand a mare and foal with a picture perfect foaling and no indication of problems is unlikely to have problems. If the problem is caught in the first 24 hours before infection develops it can be prevented with a simple transfusion. You must decide if spending the extra 50 to 10 dollars for the test is worth while. I usually put it to the clients this way, “if you would spend 500 to a 1000 dollars on treating a sick foal with a guarded to fair prognosis, do the test”. Of course when ever there are risk factors present, I always strongly recommend the test as long as the cost of the transfusion, if the test shows problems, is not prohibitive.
