Insufficient colostrum intake can reduce a foal's ability to combat infectionLast time we began discussing things that could go wrong with a foal from day one but were correctable. Now for one more.
Failure of passive antibody transfer (FPT, but shouldn't it be FPAT?) and neonatal isoerythrolysis (NI) are both conditions in foals related to the mare's colostrum. In FPT, the foal does not get enough colostrum. In NI, it does get enough, but with the wrong antigens.
We will begin with FPT, but first we will go over how the foal receives antibodies via colostrum.
Antibodies are selectively transferred from the blood of the mare to the colostrum in the last 2-to-4 weeks of pregnancy, probably as a result of hormone (estrogen and progester-one) level alterations during this time. These are antibodies against a variety of the common microorganisms to which the mare has been exposed (hence the recommendation to give the mare a tetanus toxoid booster approximately one month before she is due to foal).
The foal depends upon this supply of antibodies (primarily IgG) in the colostrum for protection against pathogenic and opportunistic microorganisms which may confront it in its first few weeks until it has the ability to produce its own. The absorption process of the colostral antibodies is complicated and we need not go into it here. Suffice it to say the antibodies are absorbed through the small intestine and enter the foal's circulatory system, where they can be measured a few hours after nursing, reaching levels approximating those of the mare at about 24-to-36 hours after birth. At about 24 hours after foaling, the small intestine loses its ability to absorb the antibodies. These antibodies are essentially gone from the foal by 90-to-180 days. Somewhere in this time frame, say 90-to-120 days, a vaccination program for the foal should begin, in response to which it will then create its own antibodies.
FPT, then, occurs when the foal does not receive sufficient antibodies in the colostrum, making it less able (or unable) to combat pathogens it may encounter. Any infection it may get becomes very serious, and death is often the outcome.

Causes of FPT
There are three possible causes of FPT: 1) colostrum low in antibody levels; 2) inability of the foal to absorb the antibodies; and, most common, 3) failure of the foal to receive colostrum.
Number one occurs in foals of improperly vaccinated mares.
Number two occurs infrequently and unpredictably. Stress (on the foal) may be involved, but it may also occur when the foal cannot (or will not) nurse for a prolonged period following foaling, during which time the gut's ability to absorb the antibodies is decreased.
Number three is probably responsible for 85% of the FPT normally seen in practice. The agalactic mare, though rare, does not pass antibodies or anything else to her foal for obvious reasons. Agalactia need not be dwelled upon; just remember that you must round up some colos-trum for your foal quickly, in addition to milk replacer (or mare replacement) if the mare does not give milk.
Severe dystocia may cause a mare with a seemingly normal bag prior to the dystocia to not have a bag at all after the foal has been straightened out and delivered (or removed surgically). This is undoubtedly stress-related, and the milk usually returns but, by the time it does, her foal is too old (12-to-24 hours or more) to benefit from her colostrum.
Prematurity (usually defined as foaling before 320 days of gestation) is a problem as well. Although the preemie foal's gut has the ability to absorb antibodies, the mare has not yet produced colostrum.
The most common cause of a foal not receiving colostrum is lack of colostrum in the mare's milk when the foal is able to nurse. A major reason for this is the mare streaming milk prior to foaling so the colostrum is lost. This may occur as a result of several situations, all involving hormonal changes and including prolonged gestation (355 days or more), placentitis, twinning, premature placental separation, and the occasional mare who thinks some other mare's foal should be hers and lets her milk flow when the other baby is seen or heard.
The levels of passively acquired antibodies in a foal may be measured in a serum sample. An IgG level of 400 mg/dl is accepted as the minimum to satisfactorily prevent most infections. There are lab tests which will give a precise determination and quick field tests which will give an accurate estimation, but the main problem lies in timing. The minimum 400 level may not be reached until the foal is 24 hours old. By the time it is learned that there is a deficiency, the foal's small intestine has lost the ability to absorb antibodies and antibody-rich colostrum cannot be given successfully.
However, if it is known ahead of time that there is a good chance the foal may be deprived of colostrum (the mare has no udder development as the calculated foal date nears or the mare has been streaming milk for 2-to-3 weeks), a little preplanning proves beneficial.

Treatment of FPT
In areas where horse breeding is a major industry, there is often a source of frozen colostrum; a vet clinic or a nursemare operation may well have a supply available. Get some, thaw it, and have your vet give it via stomach tube.
If you are in another area, you can build your own colostrum bank. If a mare presents a dead foal or one which dies within a few hours of birth, milk her out several times over the next 12-to-18 hours and freeze the product. Colostrum may also be borrowed from another mare if you are fortunate enough to have one foal at the same time or know someone who has such a mare. Two-to-four ounces may be taken from a mare every three or four hours without adversely affecting her foal. Just in case, it is a good idea to plan ahead; borrow from a foaling mare and freeze it, then you will have it when (if) you need it.
If, however, colostrum just is not available, oral administration of plasma or serum will solve the problem. Because plasma and serum contain lower antibody levels than colostrum, a very large amount-a few liters-may be necessary.
If you learn at 24 hours of age that your foal is antibody deficient, the remedy becomes a little more challenging but is still manageable. Intravenous plasma should be given, paying attention to the donor, which we will cover in next month's epistle on NI.
Also, general nursing care and protection from stress are necessary in the FPT foal until the time its own system kicks in.
One last thought on FPT: If a foal is slow to nurse, for whatever reason, and after about 4-to-6 hours it still has not, milk the mare and intubate the foal with the colostrum. Then you have a little more time to hook the little guy up.
Occasionally, and I do not know how often this happens, a foal's 24-hour serum sample will contain extremely high antibody levels-2,000 or higher. I do not know why, but these foals will frequently become very sick. Watch them.
Next time, neonatal isoerythrolysis. Stay tuned.