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From The Ivory Tower | Early Foal Immunizations
Implementation of an effective vaccination program on your farm is key to protecting your horses from infectious diseases. Vaccination of foals is intended to stimulate the immune system of the foal to produce antibodies, a process termed active immunization. For the majority of foals, we typically wait to begin our vaccine protocol until the maternal antibodies have waned. Maternal antibodies may be present in the foal for 3-4 months in most cases and up to 6 months or more in some foals.
Material antibodies are immunologically active substances that delivered to the foal in the colostrum within the first 24 hours of life. In addition to antibodies, colostrum contains white blood cells, water, protein, fat, minerals, vitamins, and carbohydrate in a thin, yellow serous fluid. The production and ingestion of equine colostrum is a complicated subject. Mares produce a limited amount of colostrum at the time of parturition (birth) and the “quality” can vary greatly. Additionally the type and concentration of antibodies in the colostrum will be dependent on the vaccination history of the mare (i.e. she will only pass on antibodies towards those diseases for which she is vaccinated against). On the foal’s end, timing is everything. The foal is able to absorb the antibodies in the colostrum through the GI tract mucosa and shuttle them to the systemic circulation, however this route is only “open” until the foal is 24 hours old. It is important to note that the antibody absorption and subsequent passive immunity in the foal declines steeply after 16 hours of age.
Simply said, ingestion of good quality colostrum before 16 hours of age is the most important event in a foal’s life! That might seem like an exaggerated statement, however without colostrum the foals essentially has no – and I mean zero – immune system to fend off pathogens. If you have any uncertainty over whether the mare was producing adequate colostrum or the foal was able to actively, successfully suckle, then you should contact your veterinarian as soon as possible.
Getting back to the business of vaccinating foals…
Based on past research, historically the veterinary community has thought that the presence of maternal or passively derived antibodies in the foal may interfere with or inhibit the immune response of foals to vaccinations. In addition, it has been reported that foals vaccinated early in life when maternal antibodies are still present may fail to respond to even a series of booster vaccinations against specific pathogens administered the following year. In other words, the standard thinking in the veterinary community is that beginning foal vaccinations early in life is not advantageous – and may be detrimental.
New research from Kansas State University evaluating the immune response to early vaccination in foals demonstrated that foals are capable of immune activation after a three-dose immunization series with a multivalent vaccine despite the presence of maternal antibodies. In this study, immune indicators in foals vaccinated at 3 months of age were comparable to those in foals initially vaccinated at 6 months of age. Therefore, in high-risk situations in which immune activation may be required earlier than at the completion of a conventional vaccine series, the data support that foals can respond to immunization that is initiated at 3 months of age provided that immunization protocols include three doses (initial immunization and two boosters) followed by a booster at 11 months of age.
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