As a mare enters the last few months of pregnancy, nutrient requirements increase because the unborn foal is growing more rapidly, averaging I pound/day. During this time, a mare in good condition will not require more total feed daily, but the concentration of protein, energy, calcium, phosphorus and Vitamin A in the feed must increase. Nutrient balance is of major importance, since most fetal growth occurs during the last 4 months of gestation. It is during the tenth month that the largest amount of mineral retention occurs in the unborn foal. Therefore, adequate nutrition of the mare is critical for normal fetal development.

In late gestation the mare should receive about 1.5 to 2.0 percent of her body weight in total feed daily. If top quality (minimum 18 percent crude protein) alfalfa hay or legume grazing is the source of roughage, the concentrate being fed should usually contain about 10 percent crude protein. Mares receiving typical quality (7.5 percent crude protein ) grass hay or grazing, or average quality alfalfa (15 percent crude protein), will usually require a higher protein concentrate such as a 14 percent mix. Careful attention to the protein balance of the diet at this stage can help prevent problems with foal growth.

Brood mares that were previously maintained solely on hay or grazing should be introduced to grain feeds slowly. Likewise, mares being switched from grass to legumes should be changed over gradually so as to minimize digestive upset.

Some brood mare operations may use small grain pastures for mares in late pregnancy, in which case mares will normally receive most of their requirements from oats, ryegrass or wheat pastures. However, some supplemental feeding (10 percent crude protein) may sometimes be needed to maintain body condition.

Feed grade rendered fat can be incorporated into the concentrate to increase the energy content of the grain feed rather significantly. When such a ration is prepared, the owner should not mix large amounts of feed that will require lengthy storage. These fat added rations can become rancid and cause mares to go "off feed."

Research has shown that high fat diets can put weight on mares that are in unsatisfactory body condition. The advantage of feeding fat in late pregnancy is that body condition can be improved without having to feed excessive amounts of concentrate on a daily basis. With a 5 percent added fat ration, a mare usually can be maintained in the same body condition with 7 to 15 percent less feed (by weight) compared to a similar grain mix with no added fat. However, fat-added mixes should be introduced to horses slowly and the grain mix should not contain more than 10 percent added fat.