IgG (immunoglobulin G) is transferred from the mare to the foal via the colostrum and provides the antibodies the newborn foal needs to fight disease and infection. The concentration of IgG in colostrum declines to a critical level of 10g/litre at different rates in individual animals. In some mares, this value can be reached as early as eight hours postpartum, or perhaps sooner, but some mares may have IgG in their colostrum up to 19 hours. To err on the side of safety, collect colostrum for banking within 4-6 hours of foaling. Mares that pre-lactate or drip colostrum for several days before foaling should be milked and this colostrum saved for her foal when it arrives. If the colostrum that is pre-lactated is not collected, the "first milk" that the foal actually drinks from its mother may not have sufficient immunoglobulin content for protection and the foal may require supplementation. This mare's colostrum should not be banked!

When collecting, analyse a small portion of each sample of colostrum for IgG and neonatal isoerythrolysis (NI) antibodies before using or banking. On the farm, you can use a colostrometer (modified hydrometer) to measure the specific gravity which indicates the IgG concentration. Specific gravity should be greater than 1.06. A concentration of 50 g/litre of IgG is ideal. To obtain exact IgG values, samples must be submitted to the laboratory. Your vet can tell you how to get a colostrometer, and where to send your colostrum samples for analysis.

If the serum isoantibody status of the pregnant mare is unknown (don't know if she has NI antibodies in her blood), it is safer not to save her colostrum if you can't have the colostrum screened by a qualified laboratory. If a potential donor mare is identified, this mare can be checked for NI antibodies prior to foaling. If you want to bank colostrum and screening is not available then milk primiparous mares (mares having their first foal).

There is a large difference in IgG concentrations in colostrum between mares. A greater yield of milk might result in a lower IgG due to dilution. Colostrum with concentrations greater than 10 g/litre can be stored for future use but the higher the concentration of IgG the better. Collect from mares preferably less than 15 years of age. Mares 4-10 years old are likely the most suitable candidates for colostrum collection.

Mares with gestation periods of 335-345 days have been shown to have higher colostral IgG concentrations. These levels decrease with either shorter or longer gestation times. There may be breed differences, Standardbreds can have lower values than some other breeds such as Arabians and Thoroughbreds, but results are conflicting so it is best to test a small amount of each sample collected from any breed.

Once a mare has foaled, you could milk a sufficient volume of colostrum, give some to the foal by bottle and then milk the remainder for banking. However, beware that this could be a problem if you havenŐt checked colostrum IgG values. If there is less than 50g/litre concentration and the foal is given the recommended 400 mls. by bottle, it is possible that the foal may not be getting sufficient protection. Lack of solar radiation and wet, cold climate conditions could result in lower IgG concentrations in colostrum, therefore, supplementation may be necessary. Volumes of 200 to 400 ml ( 7 ozs. or 7/8 of an Imperial cup) up to a litre or more are recommended for supplementation. The older the foal, the larger the volume recommended. Give to the foal within 12 hours of birth.

To evaluate the success of the passive transfer of antibodies to the foal, measure foal serum for IgG levels approximately 15-18 hours after the foal has had its first drink. This allows for sufficient time for the antibodies to be absorbed by the foal. If foal serum IgG is less than 8 g/litre and the foal appears to have a problem, plasma therapy may be indicated. Otherwise, a postsucking foal serum IgG greater than 4 g/litre should provide adequate protection.

Don't forget these are quantitative measurements and not qualitative! Vaccinate mares late in gestation to increase titres and improve the quality of the colostrum or "first milk".

1. Wash udder.
2. Wash hands.
3. Collect in a clean plastic or glass cup - do not use a metal container.
4. Milk from both sides of the udder and collect within 4-6 hours postpartum.
5. If colostrum appears dirty, filter through new cheesecloth.
6. Check each sample for IgG concentration and for NI antibodies.
7. Label with date, breed, volume, mare identification and IgG concentration and NI status.
8. Store in plastic bags in freezer and thaw at room temperature. Frozen colostrum can be stored for approximately 2 years.

By Leslie Huber, D.V.M. Equine Research Centre Guelph, Ontario, Canada

Download a printable version of this article.
If you do not have Adobe Acrobat installed, click here.