As each new year dawns, so too does a new Thoroughbred foaling season. As we saw at the Keeneland January Horses of All Ages Sale earlier this month, some arrive earlier than others, as several of the mares cataloged as “in-foal” were accompanied into the sales pavilion with their newborn foals, just days old.
One thing each and every foal has in common is the crucial need for colostrum within the first minutes and hours of their birth. This “liquid gold” is rich in antibodies and can be the difference between life and death for a foal.
Unlike humans, horses do not transfer antibodies between the mare and the fetus in-utero via the placenta. That means that at the time of birth, a foal has virtually no immune defense against infectious diseases, as their immune systems are far from fully developed.
Colostrum is the first milk produced by the mare after birth and is only produced once per foaling. Antibody-rich, the milk is thick and sticky, with a yellow hue.
“The mare's colostrum contains antibodies to any pathogens that she has been vaccinated for and antibodies to any pathogen she encounters in her day-to-day life on the farm,” said Dr. Bill Gilsenan, VMD, Dipl. ACVIM, of Rood and Riddle Equine Hospital.
While a foal is born with an immune system, it cannot tolerate the invasion of bacteria the way a healthy adult immune system can. By ingesting the colostrum, the foal will have protection against the most common bacteria in its environment until the immune system is mature enough to offer protection – at about eight to 10 weeks old.
A foal can absorb the antibodies through its gastrointestinal tract for only a short window of time. Ideally, the foal should stand and nurse from his mare within the first hours after birth in a process called passive transfer. From eight hours on, the gut's ability to absorb the protein molecules steadily declines, and by 24 hours after birth, the foal's system can no longer glean necessary antibodies from the colostrum.
“It is important for a veterinarian to evaluate a foal within the first 24 hours of life,” said Gilsenan. “A stallside blood test can be performed to determine if an adequate amount of antibodies has been ingested and absorbed by the foal.”
Failure of passive transfer can happen for a variety of reasons, including:
- The foal's inability to stand and nurse within the first hours of its life
- The mare's inability to produce a high enough quality or quantity of colostrum
- The mare “waxed up” (the term used to describe a mare dripping milk from her teats, which often signals that she will be foaling in the coming days) early and lost much of her colostrum before going into labor. Older mares are more susceptible to waxing up early and losing significant amounts of colostrum before foaling.
When this occurs, colostrum from another mare is a suitable alternative to ensure the foal receives the proper antibody defense for its first few months of life.
Luckily for horse owners, many veterinary practices keep a colostrum bank for such instances. Braxton and Damien Lynch, owners of Royal Oak Farm in Paris, Ky., say that failure of passive transfer is rare.
“We haven't had it happen very often, but when we have a mare who doesn't produce quality colostrum or enough of it, we use colostrum from vet clinics,” said Braxton Lynch. “Luckily, we've never had trouble locating colostrum when we've needed it.”
Colostrum banks are filled with colostrum collected from mares whose foals have not survived or from mares who produce a volume of colostrum that exceeds their foal's needs, and is collected from both mares admitted to the hospitals and from mares on farms serviced by the hospitals.
Lynch added that when the farm has a mare known not to produce enough colostrum, they use Domperidone to encourage increased milk production from the mare.
Gilsenan says the visual appearance of colostrum is generally a good indicator of its quality.
“Good quality colostrum should be thick, yellow-gold in color, sticky and viscous,” said Gilsenan. “If the colostrum is white in appearance or is thin and watery, it is likely of poor quality.”
However, visual assessment is not foolproof, which is why veterinarians or farms can use a Brix refractometer to determine the optical density of a sample of colostrum.
“The optical density correlates well with the antibody content of colostrum and will be a good indicator of the quality of the mare's colostrum,” added Gilsenan.
Even if it seems the foal nursed and the quality or quantity of colostrum is satisfactory, a blood test performed within 24 hours of the foal's birth can identify if he or she does not have an adequate amount of antibodies in the blood (failure of passive transfer).
“If the foal does not have an adequate amount of antibodies in the blood the veterinarian can intravenously administer hyperimmune plasma to the foal,” said Gilsenan. “This plasma is a blood product that is collected from hyperimmunized horses and contains a high concentration of antibodies and therefore provides many of the benefits that colostrum would.”
Gilsenan said advances in technology and veterinary medicine have resulted in several useful colostrum supplements. These products, he warns, are not colostrum replacements.
“These products can be useful, but do not act as a substitute for colostrum,” said Gilsenan. “No matter how far we advance technologically, it is difficult to beat the quality and content of the colostrum that the mare's body is able to produce.
Gilesnan encouraged careful monitoring on the part of foaling barn personnel to ensure a newborn is getting the amount of colostrum it needs. If the foal seems to be continuously nursing or seems restless, check to make sure the mare is producing enough milk. If the udder is unusually small and little to no milk comes out when you squeeze her teat, the mare may have agalactia (lack of milk production). This has a variety of causes, the most common being Acremonium coenophialum, a fungus found in fescue. Fescue toxicosis can cause a variety of issues in mares, including dystocia and reduced milk production and can affect an entire herd of mares if not identified and irradiated.
Farms that have more than five foals per year should consider keeping their own colostrum bank for use in emergencies, as colostrum can be frozen and stored for up to two years. Healthy mares can be used as colostrum donors, as can mares who lose their foals during or shortly after labor.
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