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Feeding Broodmares in Late PregnancyBy Dr. Peter Huntington · December 13, 2011

After seven months of gestation, the equine fetus begins to develop rapidly, and the mare's nutrient requirements becomes significantly greater than early-pregnancy needs. Energy requirements only increase approximately 15% during late pregnancy, but protein and mineral requirements increase to a greater extent because the fetal tissues being formed during this time, namely muscles and bones, are high in protein, calcium, and phosphorus.

Trace mineral supplementation is crucial during late pregnancy. Because mare’s milk is quite low in iron, zinc, copper, and manganese, the fetus stores these elements in its liver for use during the first few months of its life. Vitamin A is critically important for the late pregnant mare, especially if the mare is maintained on hay alone without access to green pasture or vitamin A supplementation. The growth rate of the foals will be reduced significantly because the vitamin A content of hay that has been stored for weeks or months is reduced.

Selenium and vitamin E supplementation in late pregnancy will enhance immunity in both the mare and foal. Antibody levels are higher in the foals of mares receiving 3 mg of selenium and 1,600 IU of vitamin E each day compared with those receiving 1 mg/day of selenium and 800 IU of vitamin E/day. Selenium may also reduce the risk of retained afterbirth.

If you prefer to feed straight grains, oats are always the first choice for energy, together with adequate vitamin and mineral intake. Preferably, use either complete premixed feeds or supplements containing appropriate levels of the vitamins and minerals. Remember that many commercial feeds designed for broodmares are formulated for Thoroughbreds, and feeding rates for other breeds can be significantly less than the recommended rate on the label. Rates of feeding also depend on the size and age of the mare. Warmblood and draught-breed mares in late pregnancy, particularly, often receive excess energy when they are fed a diet formulated to supply adequate protein and minerals to the developing foal. If the pregnant mare becomes fat during late pregnancy, the feed should be gradually changed to comprise more concentrated protein and minerals so that less can be fed each day.

Some mares may be able to continue on pasture alone with a vitamin and mineral supplement even in late pregnancy and not lose condition. Knowledge of the individual horse and her body condition are the guide to designing the feeding program.