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Nutrition of Mares in Late PregnancyBy Kentucky Equine Research Staff · November 1, 2017

Offering topnotch nutrition remains part and parcel to broodmare management, no matter the stage of pregnancy. As pregnancy advances to the last three or four months, though, mare owners should re-evaluate feeding strategies to support the upswing in energy and other nutrients necessary for rapid growth of the fetus.

“Broodmares are no different than other horses in that good-quality forage provides the underpinning for any sound diet. Consider good-quality pasture or hay ground zero and build on it,” said Catherine Whitehouse, M.S., a nutrition advisor for Kentucky Equine Research (KER). Reject dusty or moldy hay, as well as any forage that contains an abundance of impurities such as insect swarms, unidentifiable weeds, twigs, or thorns.

“Once a suitable forage has been hit upon, the remainder of the diet should be tackled. How to attack that depends largely on a mare’s metabolism,” Whitehouse continued.

Most mares can be placed in one of three categories: easy keeper, moderate metabolism, or hard keeper.

Easy keepers. Mares with access to high-quality forage might be able to maintain body condition on forage alone, even in late gestation. Forage will not, however, provide the mare with the upsurge in nutrients required for optimal fetal development. Herein lies the dilemma.

“When these mares are fed a fortified concentrate at the lowest recommended levels, they often become too fat. Obese mares can sometimes have trouble foaling and never-ending obesity sets the stage for metabolic problems, so it is best not to let mares get too heavy,” warned Whitehouse. What to do?

The best way to provide these mares with appropriate nutrition is through a ration balancer, which is a concentrated pelleted feedstuff that ensures all vitamin and mineral needs are met, particularly calcium and phosphorus. Intake rate of a ration balancer is significantly less than a conventional textured or pelleted feed, about 1-2 lb (0.5-1 kg) daily. Do not expect a mineralized salt block to provide mares with vitamins or minerals necessary for late pregnancy.

Moderate metabolism. Many mares fall into this category. The nutritional demands of late pregnancy cannot be fueled by forage alone, so they should be offered a well-formulated textured or pelleted feed intended for breeding mares. Feeding recommendations differ from one product to another but generally range from 6-14 lb (2.8-6.4 kg) per day.

“In order for mares to receive the level of nutrition intended by the manufacturer, they must consume at least the minimum amount suggested. For mares on the bubble of being easy keepers, it’s tempting to feed less than the recommended amount. Resist that urge,” Whitehouse cautioned. Feed amounts can be adjusted as pregnancy advances so moderate to moderately fleshy body condition (think a 5 or 6 on the body condition scorecard) can be maintained.

Hard keepers. These are by far the most frustrating mares for owners, as hard keepers always seem a bit ribby regardless of the diet. As far as forage is concerned, additional calories can be proffered through the provision of a good-quality alfalfa (lucerne) or alfalfa-mix hay. All mares benefit from constant access to forage, but hard keepers seem to do especially well when high-quality pasture or early-maturity alfalfa is available. Textured or concentrated feedstuffs formulated for pregnant mares should be fed at the recommended rates. These mares likely require feed quantities on the high end of recommendations, sometimes up to 14 lb (6.4 kg) each day. Meal size should not exceed 5 lb (2 kg). If necessary, feed mares two or three well-spaced meals a day.

Need more energy? “An easy way to bump up calories is through the use of a vegetable oil or stabilized rice bran top-dressed onto the feed. Always add fat-rich supplements slowly to the diet so mares become accustomed to them gradually,” Whitehouse said.

Late pregnancy is the best time to increase body condition of mares that are known to drop weight quickly during early lactation, according to Whitehouse. If, for example, you know a mare rivals a Jersey cow in milk production and you know that her weight will fall off as lactation progresses, you can try to offset this by allowing her a bit more condition prior to birth. Treating mares as individuals helps mare owners fine-tune their management.

Mares on high-grain diets can be supplemented with EquiShure, a buffer that keeps the pH of the hindgut in a steady state. Developed by KER, EquiShure reduces the risk of hindgut acidosis and associated signs, including inappetence, recurrent mild colic, loose manure, and some stable vices, all problems counterproductive to a mare’s well-being.

All mares should have fresh water and salt available.