Equine Health Update Issue 2 Volume 19 - Page 14

EQUINE | Equine Disease Update Foal Health Article reprinted from The Horse, March 2017, page 37. The Horse is published by The Horse Media Group LLC. Maureen Gallatin ; Stacey Oke, DVM, MSC Understanding Foal Immunity F oals have a functional immune system in utero— but it’s one appropriate to an unborn foal in a sterile and protected environment. Once that baby hits the real world, he needs real-world immunity. David W. Horohov, PhD, of the University of Kentucky Maxwell H. Gluck Research Center, in Lexington, de- scribed aspects of mare and foal immunity that are use- ful in everyday management. With six layers of placenta separating the mare’s cir- culation from the fetus, only small molecules can get through to the foal. Large proteins, such as antibody molecules, cannot. A lack of antibodies leaves the new- born foal unprotected against infections. So it depends on the mare’s colostrum (her antibody-rich “first milk”) to provide the necessary antibodies through a process called passive transfer. Of course, the amount of antibodies the foal gets de- pends on the mare’s antibody levels, Horohov said. So, boosting her antibodies by vaccinating according to AAEP guidelines helps assure they’re sufficient. Mares also develop antibodies as they encounter pathogens in the environment, which ultimately helps foal immunity. When bacteria, viruses, fungi, and parasites bombard 14 the foal, his health is challenged. But that challenge also stimulates the immune system, helping it mature. Over time, the from-the-mare antibodies decay, so as critical as they once were, the 4-month-old foal no lon- ger benefits. By then, he’s building his own immunity. The caveat comes when foals don’t get adequate colos- trum or the colostrum doesn’t contain those critical anti- bodies. In this scenario, neonates are highly susceptible to infections. Veterinarians might recommend vaccinat- ing those young foals to protect against disease. While the young foal’s immune system won’t make antibodies as effectively as an older foal’s would, no adverse long- term effects of early vaccination have been noted, and it will help him mount a defense. Bottom line: Vaccinating the mare is the No. 1 thing you can do to ensure a foal has the best chance at fighting off most of the bacteria and viruses he’ll encounter in his early days. Evaluating Neonatal Foals and Postpartum Mares at Foal Heat Newborn foals must transition from dependence on the dam’s body to doing everything on their own. They have to make huge physiologic changes to simply survive— by beginning to breathe, digest milk, fight disease (as • Equine Health Update •