What is Failure of Passive Transfer?
Failure of Passive Transfer (FPT) is when a foal fails to receive sufficient antibodies from its mothers colostrum in the in the first hours of its life. Antibodies do not cross the placenta in horses, so the foal is born with no natural defence against infections. Foals that have FPT have a greatly increased risk of developing life-threatening infections until they are able to make their own antibodies at the age of 3-6 weeks.
Colostrum contains antibodies to infectious agents that the mare has previously encountered, including vaccines that she has received in the weeks prior to the foal’s birth. It is more concentrated than normal mare’s milk.
How does FPT occur?
There are several reasons why FPT may occur – if the mare leaks milk before foaling the colostrum will be lost or the mare may produce colostrum that is not of a high enough quality. If the foal is too slow to suck then it may no longer be able to absorb the antibodies into its blood, as twelve to eighteen hours after birth the antibodies will be digested in the intestine rather than absorbed. If the foal is exposed to stressful conditions (e.g. a traumatic birth) the period of time that antibody absorption can occur for may be reduced.
A blood sample taken from the foal can confirm the levels of antibodies it has absorbed.
Colostrum quality can be improved by vaccinating the mare a month before the due date, and quality can be measured using a colostrometer. If the mare starts to lose milk prior to foaling, it can be collected and stored in a freezer and can then be thawed upon the birth (N.B. not using a microwave, as this destroys the antibodies).
If a foal is slow to stand and suck, it can be given colostrum (either from its mother or a donor) via a stomach tube or by bottle. If it has not had colostrum within 12 hours of birth and FPT is diagnosed, blood antibody levels can be boosted using plasma from blood – either from the dam, a donor or from commercially produced plasma.
The quantity and quality of colostrum that a foal drinks in the first 12 hours of its life can influence both its immediate and longer term health and welfare.