Colostrum — or “first milk” — is the most important meal of the foal’s life. Without it, he is at high risk of dying from infections that would normally be insignificant. While most mares produce plenty of colostrum, which the foal gobbles up, sometimes this passive-immunity transfer process fails. When it does, and the foal doesn’t receive that precious colostrum in time, you have a significant problem.
Passive Immunity Transfer
A physiological trigger close to the time of birth stimulates the mammary gland to begin concentrating immune proteins/antibodies from the blood. Concentrations in the dam’s blood serum begin to drop as they rise in colostrum so that at the time of birth the level of antibodies in the mare’s milk is several times higher than in her own blood. In addition, the colostrum contains antibodies produced locally in the mammary gland. These will reflect bacteria and other organisms present in the environment. These antibodies remain at the level of the gut lining rather than circulating in the blood, providing local protection to the intestinal tract.
The activity and concentration of antibodies present in the colostrum depends directly on the levels present in the mare’s blood and mammary gland immediately prior to birth. The highest antibody levels will be against those organisms the mare constantly encounters or was recently exposed to. This is why it is so important to house mares on the premises where they will be foaling at least four weeks in advance of the birth. It is also the reason behind vaccinating mares close to foaling with vaccines directed against diseases the foal is likely to encounter in the first four months of life (see vaccination article, February 2000).
While it may seem that the fetus should build immunity by absorbing antibodies from the mare during gestation, in reality the placenta blocks the transfer of large molecules to the fetus before birth. Since the fetus can’t produce these antibodies until close to birth, the foal is born without them. The new foal must receive a source of preformed antibodies to the common bacteria and viruses in his environment to be able to successfully ward off any infection. The process of providing preformed antibodies is called “passive transfer.”
Once the foal is born, he has less than 36 hours to absorb as many colostrum antibodies as he can. As a matter of fact, truly efficient absorption lasts about 14 hours, and peak absorption occurs about six hours after the colostrum is first ingested.
This is easier to understand when you learn that intact antibodies, like those found in colostrum, are very large molecules, larger than would be absorbed by normal intestinal tract cells. When the foal is born, his intestinal tract contains specialized cells that can absorb these large molecules intact. Plus, the colostrum contains specialized transfer molecules that assist in moving the antibodies out of the specializing absorbing cells and into the system that will transfer them to the blood. After the 36-hour mark, these specialized cells are replaced by normal cells.
Failed Passive Transfer
Without colostrum or a colostrum substitute, chances are great that the foal will experience a life-threatening infection within the first month of life. Inadequate intake may result from either mare- or foal-related problems. On the mare’s side, the most common cause is the mare beginning to lactate too early and losing her colostrum before the foal is born. Colostrum is produced only once per pregnancy — regardless of when the foal actually arrives.
Premature lactation may occur spontaneously, especially with mares that are older and have had many foals. More commonly, it may be caused in mares of any age by placental infections or a premature separation of the placenta from the uterus. Low-grade placental infection is believed to be the most common cause of premature lactation and colostrum loss. Twin pregnancies also commonly cause early lactation, sometimes as much as several weeks in advance of foaling.
The mare probably won’t appear ill in any way but will begin to bag up and then leak milk early. Slow dripping for a few hours before foaling may not be serious, but a slow drip over several days definitely is. Mares that actually run/stream milk for several hours or more before birth should be assumed to have lost their colostrum, so measures should be instituted immediately to get replacements if the mare was not milked and the colostrum saved.
Far less common is a mare who does not properly “let down” her milk after foaling. This is more likely to occur with nervous and/or maiden mares having their first foal. If the mare allows the foal to attempt to nurse but doesn’t let down milk, the vet can administer the hormone oxytocin to help.
The only significant foal-related factor is failure of the foal to successfully nurse and/or take in enough colostrum. This is primarily a problem with weak, premature or neurologically abnormal foals that cannot stand and effectively nurse. Most veterinarians will elect to milk the mare and deliver about a quart of colostrum by stomach tube if the foal has not nursed by two hours of age. This may need to be repeated for foals that continue to be unable to stand and nurse, for a total of at least two quarts of colostrum, preferably within the first six hours of life.
Problems with the foal absorbing colostrum despite taking in adequate amounts at the right time have been suspected but never actually proven.
Since you rarely know in advance a problem will occur, being prepared is largely a matter of knowing what to do and having resources lined up:
1. Be sure you have a vet who has seen the mare at least once during the pregnancy and knows he/she is your vet. Trying to find one on an emergency basis, especially in the middle of foaling season, is not a good situation. Alert your vet when your mare is within two weeks of her due date and at other appropriate intervals (e.g. if your milk calcium testing indicates foaling likely within 24 to 48 hours).
2. If the mare begins to leak milk, notify your vet to discuss a monitoring and management plan. You can save yourself a lot of headaches — and get the best outcome for the foal — if the leaking mare is milked and her own colostrum saved. If you find the mare streaming milk, collect a small sample and get it checked by your vet for immunoglobin levels as quickly as possible. If it is colostrum, start collecting it immediately. If rapid testing is simply not possible, collect the milk anyway. Use heavy plastic freezer bags and freeze the milk at ?”15?° to ?”20?° Centigrade (5?° to ?”4?° Fahrenheit). A sample can be kept in the refrigerator for 24 hours or so to be tested for immunoglobin levels. Collect a total of about two quarts.
3. Check with your vet, other vets, clinics, and breeding farms to locate sources of frozen colostrum and/or colostrum replacers. Be sure they are well stocked and can supply you immediately.
4. If your mare foals uneventfully, after your foal has first nursed, then collect six to eight ounces of her colostrum to be frozen as above in case you run into problems next year (assuming you’re going to breed her again). This amount can be collected from normal mares without depriving the foal and give you some peace of mind and valuable insurance in case of future problems.
Frozen colostrum can be kept for a year at these temperatures but once thawed must be used. If you’re willing, you could even collect colostrum to freeze just so your veterinarian can have it on hand for another needy breeder.
Contacts: Seramune ($69/300 ml.) United Vet Equine 800/328-6652; Fastrack Probiotic Gel ($20/20 cc tube) Conklin 612/445-6010.
Also With This Article
Click here to view ”Colostrum Replacements.”
Click here to view ”Case History: Adarlin And Son.”
Click here to view ”Domperidone And Colostrum.”
Click here to view ”Testing Foals For Adequate Passive Immunity.”
Click here to view ”Further Support.”