Photo: Anne M. Eberhardt

Now that foaling season is here, equine veterinarians who routinely treat and care for foals will be thinking about colostrumwho has it, who needs it, and where they can get it. You might wonder if colostrum actually is that important. To a newborn foal, it can mean the difference between life and death.

To discuss why colostrum is so important, I first have to explain about the precarious situation into which a foal is born. We all know that to fight infection, healthy people and horses have a functioning immune system that can mount a response, in the form of specialized cells that kill invading bacteria. The foal is born with an immune system that is intact, but is not born with any circulating (within the bloodstream) antibodies that can fight infection.

The foal isn't born with antibodies derived from the dam's bloodstream as is the case with humans. The foal, while in the uterus, has a bloodstream that is separated from the dam's bloodstream by the placenta, which in the horse has six layers. These layers do not allow particles as large as immunoglobulins (antibodies) to cross, so the foal cannot derive antibodies from the mare and is born with little to no circulating antibodies.

The newborn foal's immune system is intact and can function, but it does not respond to invasion by bacteria as quickly as the immune system of an adult. This slow response or lag time can allow bacteria that the foal encounters in its environment to wreak havoc and create overwhelming infection, unless the foal has nursed and absorbed an adequate amount of colostrum.

What Is Colostrum?

Colostrum is produced by the mare only once per pregnancy and is the first milk she produces just before she foals, and for not more than 24 hours after giving birth. This milk is thick, yellow, and very sticky, which differs from the milk she will produce later (which is thin and white). As the mare nears her foaling date, her udder will begin to fill with colostrum. As she begins to produce milk, it will drip off the ends of her teats. This process is known as "waxing" because the dripping colostrum is thick and looks like wax dripping from a burning candle.

This colostrum is full of immunoglobulins that the mare's mammary gland has concentrated from her bloodstream. These immunoglobulins (gamma globulin is the most prominent) will give the foal protection from invading bacteria and will help keep the foal healthy until his own immune system is adequate, at about eight-10 weeks of age.

The foal must drink and absorb colostrum within the first 12-24 hours of life. The immunoglobulins within the milk only can be absorbed by the foal's gastrointestinal tract during a small window of timethe first 24 hours of life (the peak time for when the intestine can absorb the most is within the first eight hours of the foal's life). After that time, the foal's intestinal tract cannot absorb the larger immunoglobulin molecules. After about eight hours of the newborn's life, the absorptive capability declines steadily to zero, around 24 hours of life.

Fortunately, the majority of the time, the foal is born, struggles to his feet, finds the udder, and nurses well. The foal then absorbs the colostrum from his dam and has no problem. But what happens when the foal does not absorb colostrum and what can you do to protect the foal?

Failure of Passive Transfer

When a foal does not absorb enough colostrum from the mare, it is technically called failure of passive transfera partial or complete failure of the maternal antibodies being passed from mare to foal. There are a number of reasons for this syndrome to develop:

  • The mare does not produce colostrum (agalactia) or produces low-quality (low immunoglobulin level) colostrum;
  • The mare might "wax" early and drip the majority of her colostrum before the foal is born; or
  • The foal might be too weak to stand and nurse. Any of these causes can leave a foal deficient in immunoglobulin level and more susceptible to infection.

How Much?

There has been much debate about how much colostrum is required to protect the foal from infection. One study showed that one to two liters of a normal mare's colostrum should be sufficient to give a foal a high level of immunoglobulinenough to protect the foal from infection. It is difficult, if not impossible, to measure how much your foal drinks. The quantity is more important for foals which cannot nurse or have mares which lack colostrum. Most healthy foals will nurse for one or two minutes, six or seven times an hour. If your foal appears weak and sleeps a lot, he might not be getting enough colostrum. Have your veterinarian examine the foal as soon as possible.

Is Your Mare Ready?

Foremost, each mare which foals should be checked to make sure she has colostrum (milk) in her udder. You can do this just by looking and palpating her udder. A mare's udder at foaling should be enlarged, with colostrum dripping in small quantities. After washing your hands and cleaning her udder, with a gentle soap and water, you can squeeze a teat to make sure colostrum streams from the teat. If you have a mare which foals and she has little to no colostrum, call your veterinarian immediately. Your veterinarian can evaluate the mare for the reason she has no colostrum and might start treatment to help her produce milk. More importantly, if the mare is confirmed not to have enough colostrum, then your veterinarian can help you find a source of colostrum.

Colostrum can be hard to come by. The best sources are large breeding farms, large private equine practices, and university veterinary hospitals. If colostrum cannot be found, then a substitute must be administered. Equine oral immunoglobulins are available commercially, as is commercial intravenous plasma. Intravenous plasma is more expensive, but I personally prefer it to boost the immunoglobulins in a newborn foal. Your veterinarian can guide you to the best treatment for your foal and for your particular situation.

After boosting the foal's system with either oral or intravenous immunoglobulins (or after the foal has nursed the mare), then a commercial milk replacer can be used to supplement or completely feed the foal.

Is The Colostrum Good?

Subjective evaluation of colostrum is acceptable in most cases when evaluating colostrum. Remember, good-quality colostrum is yellow, thick, and very sticky. If a mare's colostrum is white and thin, then it probably is not very good quality. Colostrum can be tested using a colostrometer, which measures the specific gravity (weight of a substance relative to an equivalent volume of water) of the colostrum. The specific gravity is directly correlated with immunoglobulin content in the colostrum and should be 1.060 to achieve high levels of immunoglobulins. Measuring the specific gravity of colostrum is even more important when banking colostrum and freezing it for use in foals which are in need.

Got Enough Colostrum?

The best treatment for neonatal failure of passive transfer and subsequent septicemia (bacterial infection) is prevention. The best way to prevent these complications is to have your foal evaluated soon after birth (18-24 hours). I call it the healthy foal check.

During that examination, the foal is evaluated for any birth defects such as a cleft plate, entropion (rolling in of the eyelids), and other potential problems such as broken ribs or difficulty passing the meconium. Also during this time, the foal should have its IgG or gamma globulin evaluated by one of several different tests. There are a few tests that can be performed in the field to determine if the foal absorbed enough (considered 800-1000 mg/dl of IgG). The CITE test is the most common one used in my area.

What To Do If...

Your foal doesn't nurse from the mare because of weakness or musculoskeletal problems that prevent him from standing.

First call your veterinarian and have the foal evaluated as soon as possible. If the foal cannot stand due to musculoskeletal problems such as contracted tendons, but he wants to nurse and the mare has good quality colostrum, then the mare can be milked and the colostrum fed to the foal in a bottle. Foals with a good appetite should be fed as much colostrum as they will drink (usually around 250 ml/hour) every hour (every half-hour is even better). Normal foals will stand, nurse, then take a short nap. Then they will get up again to nurse very frequently (six to seven times an hour).

Your veterinarian should be called immediately to evaluate the foal if it cannot stand on its own, and referral to an equine hospital might be warranted for treatment.

Your foal nurses all the time, and he constantly is bumping the mare's udder and seems restless.

Check your mare's udder to see if she has any milk. If the udder is very small and does not have any colostrum or milk when you squeeze her teat, then she has agalactia (lack of milk production). This can be caused by many different reasons, the most common of which is ingestion of a fungus (Acremonium coenophialum) that grows on fescue grasses. This fungus also can lead to dystocia due to problems of a thickened placenta and prolonged gestation. Your veterinarian should be called immediately to evaluate the foal and treat the mare. These foals often require intensive treatment at an equine clinic as they are weak and usually develop failure of passive transfer with subsequent septicemia (bacterial infection), which can be fatal.

You have an older broodmare that "waxed" for two weeks before finally foaling. You lost a lot of sleep and the mare appeared to lose all of her colostrum as the milk is now white, thin, and not at all sticky. She has plenty of milk, but you worry about the immunoglobulin content.

You should call your veterinarian immediately and have him evaluate the mare and foal as well as the milk. The milk is good because it will sustain and nourish the foal, but also is bad, because it can encourage the foal's intestine to lose the ability to absorb immunoglobulins. If possible, the milk should be evaluated with a colostrometer. If colostrum is of low quality, then a colostrum source should be found. If available, one to two liters of colostrum should be administered over eight hours; then the foal can be allowed to nurse from the mare normally. If colostrum is not available, then an oral or intravenous source of immunoglobulins should be administered as soon as possible. The foal should be checked at 18-24 hours to evaluate IgG levels. Further treatment can be given if warranted.

If the foal does not have an adequate level of IgG, then supplementation should be administered, depending on the age of the foal. Since most foals are not examined until 24 hours of age, intravenous plasma is the best choice. One to two liters of plasma usually are sufficient to raise the IgG level to a safe limits. Although this treatment is expensive, it can save money in the future by preventing septicemia (the treatment for this condition at most equine hospitals is several thousand dollars, depending on complications that arise). Many owners see the use of plasma as an inexpensive safeguard.

Furthermore, some farms with very valuable foals elect to administer intravenous plasma even if the foal has an acceptable level of immunoglobulins, especially if the farm has had problems with diseases such as Rhodococcus equi. Plasma can be purchased that is hyperimmune for that disease and other bacteria. Talk to your veterinarian to determine if plasma therapy is right for your foal.

It should be noted that not all foals with a low IgG become sick. However, most foals with septicemia have an IgG less than 800 mg/dl. This might be due in part to environmental cleanliness or other risk factors inherent to a particular farm, but further discussion is beyond the scope of this article.

When Colostrum Is Dangerous

There is only one time we do not allow a foal to nurse its dam's colostrumwhen it is at risk of neonatal isoerythrolysis (NI). This is a disease that causes anemia (low red blood cell count) in the foal, and that can be fatal if not detected quickly. It is caused by the mare's becoming sensitized to certain red blood cell antigens. This can happen from a previous blood transfusion or exposure to a previous foal's blood during foaling. If this blood has an antigen that she lacks present on the red blood cells, she will produce antibodies that become concentrated in her colostrum. If her foal has the red blood cell with the offending antigen (inherited from the sire) for which the mare has produced antibodies, then after the foal ingests the colostrum, the antibodies will destroy the foal's red blood cells.

If a mare is suspected of creating antibodies through risk or from producing previous NI foals, then the mare can be tested in her last month of gestation and the determination made through a blood test.

Foals which have NI usually develop signs within 48 hours. These foals usually are weak, have pale membranes, and have elevated heart and respiratory rates. Once the diagnosis is made, foals are treated with blood transfusions and supportive care.

Luckily, this is not a terribly common disease, and if suspected ahead of time, the foal is muzzled immediately after birth and fed an alternative source of colostrum or administered oral or intravenous immunoglobulins.

Storing Colostrum

Many large equine breeding farms and equine practices "bank" or store colostrum for emergencies. If you routinely have more than a few foals per year, it would be a good idea to store colostrum for your own use. Healthy mares with high immunoglobulin content in their colostrum can be used as colostrum donors. Mares who deliver dead foals or who have foals die shortly after birth can be milked of all of their colostrum. Furthermore, healthy mares with foals also can have about 200 ccs of colostrum milked and subsequently stored and not risk depleting the foal's supply.

Colostrum can be frozen and stored for not more than two years. If you have a stash of frozen colostrum, remember to thaw it slowly in a warm water bath (for about one hour). Microwaving colostrum will destroy the immunoglobulins, thus destroying the most important ingredient.