December is an important time for pregnant mares. In the winter, many mares have to contend with increasing nutrient demands from a growing fetus around the same time pasture conditions (availability of forage) decrease.

Severe weather conditions from December to February can impose another nutritional stress. To compensate for these changes, diets fed to pregnant mares regularly should be evaluated and adjusted to meet the needs of the mare. If mares are not fed enough of some nutrients during gestation, the foal may be born weak or undersized.

"Fortunately, the metabolism of the mare protects the foal from most nutrient deficiencies by using the mare's own body stores," Laurie Lawrence, equine nutritionist for the University of Kentucky's College of Agriculture, said. "For example, if a mare is not fed enough calcium to meet the needs of fetal skeletal development, calcium will be mobilized from the mare's skeleton. Over the course of several pregnancies this "robbing" of calcium could weaken the mare's skeletal structure."

Similarly, if a mare does not get enough calories (energy) during gestation to meet the growing foal's needs, she will mobilize her own body tissue. Research has shown that slight to moderate underfeeding of energy to pregnant mares does not greatly affect birth weight of foals, but does prolong gestation and affects the rebreeding efficiency of the mare.

If a mare is thin, with ribs visible, at foaling time, she may have a harder time getting pregnant again. "Contrary to some opinions, fat mares are not at risk of infertility," Lawrence said.

In a study of more than 900 horses, mares that were fat did not have reduced conception rates compared to mares that were in moderate or thin condition. In fact, the mares with the poorest reproductive efficiency were mares that started the breeding season in a thin body condition.

To make sure pregnant mares are receiving adequate nutrients in their diets, Lawrence says to feed a good quality hay and a commercially- manufactured fortified grain mix designed for broodmares. Commercially manufactured feeds fortified to meet the needs of broodmares are superior to plain oats or other plain cereal grains since they contain adequate levels of essential minerals. Oats, corn and barley are deficient in calcium and may be low in other minerals also.

If mares are receiving a grass hay, like timothy or orchard grass, the grain mix should contain slightly higher levels of nutrients than if alfalfa or an alfalfa mix is being fed.

Tall fescue usually is not an acceptable hay for broodmares. Typical tall fescue hay is too low in nutrient value for pregnant mares. And much of it contains a fungus that can cause foaling difficulties and reduce milk production.

"To make sure a mare is consuming enough of a nutritionally adequate diet, it is important to regularly monitor body condition," Lawrence emphasized. "This can be accomplished by regular weighing, or more practically, by condition scoring once a month."

To condition-score a horse, the amount of fat over the neck, withers, back, ribs and tail head should be palpated. Visual appraisal is not as accurate, because a heavy hair coat will make many horses appear fatter than they are. A mare that is in desirable body condition will have some fat covering over the ribs, withers, spine and tail head. The fat over the ribs should feel somewhat spongy, and the back should be relatively level with the spine.

In December, it is better for a mare to be a little too fat than a little too thin, because it is very hard for most mares to gain body condition in late gestation. More commonly, mares lose body condition in late gestation because the periods of nutritional challenge from the fetus and the weather coincide with a time when appetite declines.

Winter management of pregnant mares is not impossible, but it is a challenge for managers to handle. Keeping a close eye on a mare's diet and body condition will help meet that challenge. – 30 –