Written By: Jennifer Johnson, DVM, University of Minnesota
Colostrum, or “first milk”, is the first milk that a mare makes to feed her foal. Consumption of an adequate amount of colostrum is critical to the health and well-being of the newborn foal. Colostrum provides infection-fighting antibodies , vitamins, minerals, energy, protein, fat and acts as a laxative to help the foal pass the meconium (first stool). Unlike human babies, when foals are born they have no disease-fighting antibodies in their blood. Therefore, a foal must ingest colostrum in order to absorb the antibodies needed. These antibodies are made by the mare and will hopefully provide specific protection for the bacteria and viruses in the foal’s environment. This is called passive transfer.
After 3-6 weeks of age, the foal will start making her own antibodies but often retains some protection from the mare until 4-5 months of age. Once the foal is born, it is critical that she begins because nursing as soon as possible, she is only able to absorb the antibodies from the colostrum for a finite time period. Each hour the foal is alive, her ability to absorb the colostrum lessens. Therefore, the maximum benefit from colostrum is obtained when your foal nurses soon and often. The easiest way to track passive transfer in your foal is to use a Foal IgG SNAP test, which measures the antibody level in the foal’s blood. The goal is for the reading to be greater than 800 mg/dl. 400-800 mg/dl is considered partial passive transfer. Anything under 400 mg/dl is considered complete failure of passive transfer.
There is always debate about when to perform these tests. Some breeders like to draw the blood at 12 hours. This way, if the test is low, the breeder can supplement the foal’s colostrum intake. However, this will overtreat some foals who just haven’t had time to absorb the antibodies yet. Others prefer to wait 18-24 hours to draw the blood. This way, there is no chance that the foal’s levels will go up. However, if you discover that your foal is below the cut-off level, the steps to remedy the situation are more invasive and costly.
Failure of passive transfer isn’t a disease, and there are no clinical signs to diagnose it. However, foals with failure of passive transfer are at an increased risk of pneumonia, diarrhea, infected joints, infected umbilical cords, and other diseases. Therefore, if you know your foal has failure of passive transfer, we recommend you seek the assistance of a veterinarian. The most common treatment for failure of passive transfer is to administer a plasma transfusion. This involves placing an IV catheter in your foal’s neck, and slowly administering a unit of equine plasma through that catheter. Unfortunately, even successful passive transfer can’t guarantee a perfectly healthy foal, although it should help!
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