Failure of Passive Transfer
Mares have a placenta-uterine connection called epitheliochorial placentation. This means that the mare’s blood is kept far away from the fetus and inhibits the transfer of antibodies from the mare to the fetus. Instead, antibodies are concentrated in the first milk that the mare produces. This is extremely important to keep the foal healthy after birth, as there is no time for a response to the many, many antigens that horses (and people, etc.) are exposed to daily. So this first milk that supplies antibodies is call colostrum and its intake by the foal is call passive transfer- the foal is not making its own antibodies.
Colostrum must be taken into the foal within 12-24 hours. The foal’s gastrointestinal tract is ‘leaky’ to allow the antibodies to be absorbed intact, but after 12-24 hours the cells tighten and the gut is no longer leaky; the antibodies cannot be absorbed. Absorption is best within the first 6-8 hours after birth. Foals have an immediate suckle response and stand within 1-2 hours, so they can easily take in the colostrum.
Both the mare and foal can contribute to FPT. If the foal is born too early or is dysmature, or has a limb deformity, or is septic, it might not be able to stand to suckle. The mare may have poor-quality colostrum, meaning that there are not enough antibodies present. About 1/3 of mares will not have adequate colostral antibodies. This can be due to age, nutrition, vaccination status, fescue toxicity and breed. Thoroughbreds and Standardbreds have poor quality colostrum compared to Arabians and Quarter Horses.
A very common cause of FPT is the loss of colostrum prior to foaling. Early lactation may be due to placental infection or just a very full udder. It is important to collect this colostrum and keep it frozen in case it is needed.
As alluded to earlier, foals begin to produce their own antibodies at birth, but do not have significant levels for several months. Without the antibodies obtained from colostrum, foals are susceptible to infection of the umbilicus, pneumonia, diarrhea, joint infections, and sepsis. Neonatal septicemia is a leading cause of death in the first few weeks of life. Any foal showing signs of disease should be examined by a veterinarian.
Veterinarians diagnose FPT by measuring antibody levels in the foal’s blood. This should be done for all foals in the first 12-24 hours of birth. If the levels are not adequate, intravenous plasma can be administered to the foal to boost the immunoglobulin levels.
Not all foals with FPT develop life-threatening disease, and adequate immunoglobulin levels do not guarantee that the foal will remain healthy. The prognosis for recovery from septicemia is highly variable and depends partly upon the amount of care the foal receives. Sick foals take a lot of time and effort to get them to survive.
To help prevent FPT, make sure that the mare is vaccinated 4-6 weeks prior to foaling and that the mare is not moved to new surroundings in the last month of gestation. Also make sure that the foal does stand and nurse. Most supplements on the market do not give the desired response of increasing the foal’s antibody levels.