Foals rely on immunoglobulins passed from the mare in the colostrum to protect them from infection during the first weeks of life. If the foal receives inadequate colostrum, or if the colostrum is of poor quality, it is at greater risk of succumbing to infectious disease.
Mares that foal early, or drip milk before foaling, often produce poor quality colostrum.
Methods that have been used to assess colostrum quality include colostrometry and refractometry. In colostrometry, a float measures the specific gravity, which is correlated to the immunoglobulin (IgG) content. Colostrum with a specific gravity greater than 1.06 usually contains adequate immunoglobulins. The refractometer measures the refractive index of the colostrum which, again, can be related to the immunoglobulin concentration.
Dr Monica Venner and her colleagues at University of Veterinary Medicine in Hannover have been assessing methods of evaluating colostrum that can be used "in the field" - that is, at the stable or on the farm, rather than in the laboratory.
They also wanted to identify the best time to collect colostrum from donor mares and check if the quality of the colostrum is affected by the number of foals a mare has had.
Thirty six Warmblood mares were used for the study. Samples of colostrum were collected from both sides of the udder on five occasions within the first 12 hours after the foals had been born. The foals were muzzled for the first six hours of life to prevent them sucking.
The researchers used both a colostrometer and a refractometer to measure the immunoglobulin levels in the colostrum and compared the values with those given by the "gold standard" measure of immunoglobulin, the ELISA test.
Both density (as measured by the colostrometer) and the refractive index (measured by the refractometer) gave a good indication of the immunoglobulin concentration. The refractometer was the most reliable and practical technique, but was also the more expensive.
The researchers found that there was no difference in colostrum production between the two sides of the udder. Mares foaling for the first time had the most concentrated colostrum, but the IgG concentration halved within three hours.
Mares foaling for the first time produced less colostrum than more experienced mares. (In the first three hours, the average volume of colostrum produced was 527ml and 1020 ml respectively). So the total amount of immunoglobulins first-time mares produced was significantly lower.
The results showed that mares in their third lactation produced the highest concetration of IgG. They also produced large amounts of colostrum. So Dr Venner suggests that a good colostrum donor would be a mare that has just foaled for the third time.
For more details: Investigation on immunolglobulin Gconcentration by colostrometry and an ELISA-technique in colostrum of mares.Robert G Markus, Katrin Strutzberg-Minder, Erich Klug, Monica Venner. Pfredeheilkunde (2005) 21, 119 - 120.