Foals must have adequate amounts of good quality first milk, called colostrum, within 12 hours of birth to remain healthy. Unlike most newborns, foals are born without any antibodies (immunoglobulins) to fight infection. He gets these first antibodies from the colostrum and we call this process of the mare transferring antibodies to the foal, passive transfer. Though debate about what constitutes adequate levels of antibodies in the newborn after passive transrer, one thing is certain, without some passive transfer the foal will develop infections and die. This article discusses colostrum and passive transfer in greater detail, testing for passive transfer, and treatment for it. See also Feeding Orphan Foals.

This concept of passive transfer is a bit foreign to many mare owners because the horse is the only specie they may have come into contact with where this is so important. Unlike most species, antibodies are not transferred from the mother to the baby while in the uterus. This is not the same as the baby is unable to make antibodies but when born he has not been exposed to any diseases so does not made any antibodies to them. Following exposure he can make them but by the time he does it will be too late and he will have succumbed to the disease. To tide the neonate over until he makes a set of antibodies to the pathogens in his environment he needs his dam”s antibodies to help ward off infection.

Several events and conditions have to occur for successful transfer. First the mare has to produce good quality colostrum with antibodies to the infectious organisms the foal is likely to encounter. Then the foal must consume the colostrum shortly after birth. The immunoglobulins are large protein molecules that would normally be digested to simple molecules. But for the first 12 hours following birth the foals digestive system is modified so as not to digest the antibodies and has large, at least on a molecular basis, holes in it so the antibodies can be absorbed and transferred to the blood system . These special conditions rapidly change following birth so there is a small window, less than 18 hours where this process can occur. Recently there has been a switch in emphasis on research into the the cause of the high incidence of neonatal septicemia in foals. While previously the umbilical cord was frequently implicated as the source of the infection it is now thought that perhaps this special condition of the neonates bowel may actually be the entry point for most of these infections.

There are gestational and birth conditions which are associated with a higher incidence of failure of passive transfer but any marked deviation from a normal health last month of preganancy or in the behavior or health of the newborn foal should be considered a reason to suspect possible failure. So you should first be acquainted with the normal events of pregnancy, lactation, birth, and the first 24 hours of the neonates life, ...more. Specific early alerts to possible trouble with colostrum would be:

• A history of poor nutrition or management of the mare.
• Mare in thin or worse condition.
• Grazing fescue pastures after day 300 of pregnancy.
• Premature birth (less than 325 days) or a premature looking foal.
• Milk leaking out before birth.
• A small bag with thin watery fluid at birth
• Foals slow to stand or that have trouble nursing within 2 hours of birth
• The mare rejects the foal.

Assessing Colostrum Quality

Assessing the Foal

Perhaps the first question is, "should every foal be checked?" In answering this question it is important to remember that once a foal develops a systemic infection they are very difficult and very expensive to treat. These tend to be mixed, resistant, toxin producing, blood infections.

More Information on Presented at the 2006 Am Ass of Eq Pract: Evaluation of Five Assays for the Diagnosis of Failure of Passive Transfer of Immunity in Foals by Rachel Davis and Steeve Gigue` re, DVM, PhD, Diplomate ACVIM IgG concentration in serum was assessed using zinc sulfate turbidity (Equi Z), glutaraldehyde coagulation (Gammacheck E), semiquantitative immunoassays (Midland 4 Quick Test Kit, Midland 8 Quick Test Kits the Idexx Snap test),and a quantitative immunoassay (DVM Stat). Two single radial immunodiffusion (RID) assays were used as reference methods.. Sensitivity: Except the Midland 8 test all were considered sensitive enough for screening blood. A finding of adequate transfer meant that the foal was OK with a high degree of confidence. The Midland 8 test would identify some foals as adequate which had lower levels of antibodies. Specificity: A finding of inadequate transfer was not accurate enough on all the tests except Snap test and the Midland 8 test to base treatment on in all conditions. The other tests would often identify foals as having inadequate transfer that really were OK. In conclusion it seems like you should be using only the Snap test to screen and base treatment upon.

On the other hand a mare and foal with a picture perfect foaling and no indication of problems is unlikely to develop septic infections, let's peg the incidence somewhere less than 5% for the population with no risk factors. If the problem of failure of passive transfer is caught in the first 24 hours before infection develops it can be corrected with a transfusion. You must decide if spending the extra 50 to 100 dollars for the test is worthwhile. One way to answer this is to ask yourself, "Would I spend 500 to a 1000 dollars on treating a sick foal with a fair to guarded prognosis?" If so the test makes good economic sense. Imporatant: anytime there are risk factors present the chance of failure and subsequent infection goes up so it would be strongly recommend you test, as long as the cost of the transfusion is within your budget.

What constitutes adequate immune transfer is not clear cut. We measure transfer by checking the immunoglobulin concentration of the foal?s blood 18 to 24 hours following birth. There are a number of field test kits to measure this but you have to be careful as the accuracy of the tests vary, see insert on left. Results are usually expressed in milligrams per deciliter (mg/dl). Concentrations below 400 mg/dl are considered failure of passive transfer while above 800 mg/dl is considered a good transfer. In between is considered to partial failure. However there are surveys that have found foals below 400 that remained healthy and problem free while those above 800 develop infections so the results should be interpreted in light of other factors. Concentrations around 400 may be considered adequate if all other conditions and physical findings are good. This includes a healthy mare, a healthy foal, normal placenta and a clean nonstressful environment. On the other hand concentrations under 800 should be considered inadequate if there are signs of stress or illness in the foal. To summarize:

• 0 - 400 mg/dl = Failure of Passive Transfer
• 400 - 800 mg/dl = Partial Failure of Transfer
• 800 - Up = Successful Transfer

If problems are identified in the first 12 hours oral therapy can be attempted

IV Infusion of Equine Serum Will be Necessary After 12 Hours has Passed.

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