During the last three months of gestation, fetal growth rapidly increases, thus increasing nutrient requirements. Energy, protein, calcium, and phosphorous needs increase during this time. Pregnant mares will need to be fed a more energy-dense feed to meet increasing requirements. An average- to high-quality legume, such as alfalfa, or grass cut or grazed at early maturity, may provide adequate energy and protein. If the mare is consuming adequate amounts of this high-quality hay or pasture, no grain supplement is necessary. However, many mares may not be able to physically consume enough hay or pasture to meet their nutrient requirements, and the inclusion of a concentrate may be necessary. In feeding broodmares, it is important to maintain a proper calcium and phosphorous ratio in their diet. A proper Ca:P ratio of at least 1:1, but preferably 1.5:1 or 2:1, is desirable. Feeding a balanced concentrate feed will not require the addition of vitamins.
You can read more on this page about feeding the broodmare.
There are concentrates available specifically for the broodmare that address shortfalls in nutritional requirements.
