Mare’s Milk: A Closer Look

Once a foal latches on to the mare’s udder and slurps colostrum, few breeders probably give much thought to mare’s milk unless a problem arises, such as a foal that becomes orphaned or fails to grow as expected.

“The significance of the milk is often passed over because, unless we see droplets on the foal’s muzzle or whiskers, it is not easily seen, even though horsemen know well the life-sustaining properties it possesses,” said Kathleen Crandell, Ph.D., a nutritionist with Kentucky Equine Research. “Mares usually produce first-rate colostrum and milk, sometimes at the expense of their own body condition and health if they are not being nourished properly.”

Unsurprisingly, the milk of mares provides the best nutrition for foals, while milk from other species is never quite as good. Much of this is due to nutritional composition.

How does mare’s milk stack up against other milk, say that from a cow or a goat? In terms of protein, a nutrient necessary for optimal growth, mare’s milk is similar to both cow’s and goat’s milk in total crude protein. However, not all proteins found in milk are the same.

Milk is composed of two primary proteins, whey and casein. Whey is considered a high-quality protein because it includes several essential amino acids. Mare’s milk surpasses cow’s milk with respect to whey, as mare’s milk contains about 40%, approximately double that of cow’s. Whey is thought to be better absorbed in the gastrointestinal tract than casein. The quantity of casein is about half that found in cow’s milk. Interestingly, studies have uncovered differences between mares of varying breeds in terms of protein levels, though the effect of dietary influences have not been determined.

Where does the energy fraction of mare’s milk come from, you ask? “The predominant carbohydrate in milk is lactose, a sugar that contains both glucose and galactose units,” explained Crandell. Low levels of the simple sugar glucose and galactose are also identifiable in mare’s milk. Lactose content of milk increases as lactation progresses.

The mineral content of mare’s milk is low compared to the milk of other species. Mineral concentration peaks during the first seven to ten days of lactation and then falls gradually.

To support the production of high-quality milk, mares should be fed optimally before and after foaling. “Meeting the nutritional needs of a pregnant or lactating mare is not difficult; however, mares require special consideration, particularly an elevation in calories to support fetal growth and milk production at key points in the breeding continuum,” explained Crandell.

Contact a Kentucky Equine Research nutrition advisor for help formulating a custom-made diet for your mare.

The reproductive benefits of certain nutritional supplements should be underscored. Of particular importance for mares are omega-3 fatty acids, especially docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). In mares, reproductive benefits of omega-3 fatty acids include improved colostrum quality and enhanced passive transfer of antibodies to foals. Kentucky Equine Research developed EO-3, a marine-derived source of DHA and EPA. Omega-3 fatty acids from menhaden fish oil are better utilized by the horse’s body than plant-based sources, such as flaxseed.

Stoneham, S.J., P. Morresey, and J. Ousey. 2016. Nutritional management and practical feeding of the orphan foal. Equine Veterinary Education.