For many years horse owners and veterinarians thought the nutrient needs of pregnant mares increased only at the end of gestation. But new research shows that pregnant mares' nutrient needs increase as early as the fifth month of gestation.
Early October is an excellent time to evaluate broodmares' body conditions and to determine whether adjustments are necessary prior to the next breeding and foaling season. The Henneke system evaluates horses' body condition scores (BCS) on a scale of 1 to 9; where 1 is extremely thin and 9 is extremely fat. A body condition of 5 is considered moderate.
Many research studies have documented that reproductive efficiency is impaired if mares have BCS below 5 at the onset of the breeding season. Therefore, one of the goals of broodmare feeding programs should be to have mares in a body condition of at least 5 by the end of fall.
Evaluate body condition by palpating the amount of fat in several areas on the horse: the neck, the shoulder, the ribs, the withers, behind the shoulder, and above the back and tailhead. A horse in moderate body condition will have enough fat cover that the ribs are easily felt but not visible. There should be enough fat cover on the withers, back, tailhead, pelvis, and shoulder so the body parts blend to together smoothly. Remember to evaluate the amount of fat cover manually, as a thick hair coat can be deceiving. The size of the abdomen (belly) is not an indicator of body condition and is often enlarged due to pregnancy or prior pregnancies.
Because some mares will lose body condition during the coldest part of the winter, some managers might want mares to begin winter with a BCS of 6, which is moderately fleshy. Similarly, if a mare is known to lose weight during lactation, the owner or manager might also want to keep her body condition above 5.
If a mare is slightly overweight, her reproductive efficiency will not be affected. In fact, if she is moderately fleshy at the onset of winter, she will have a small buffer of expendable body fat that can be used during severe cold or during early lactation. However, there is no benefit to a mare being extremely fat.
Body condition is affected primarily by calorie consumption. If a mare consumes the same amount of calories as she uses, her body condition will remain the same. In order to increase body condition, she needs to consume more calories than she expends. Nutritionists call this positive energy balance. There are two ways to manipulate energy balance: change calorie use or change calorie intake.
In addition to needing calories for gestation and lactation, broodmares also need calories for daily activities such as walking to food and water and to regulate body temperature. If a mare is thin, provide an environment with shelter and easily accessible food to help reduce her calorie use. However, to make a significant change in energy balance, it is almost always necessary to change her diet.
The first step in changing an underweight broodmare's diet is to evaluate her forage (pasture or hay) intake. Increase forage quality or quantity if it is low. If this does not produce the desired change in body condition, then increase concentrate intake. The amount of extra concentrate that is needed for weight gain in any mare depends on the size of the mare, the initial and target body condition, and her current diet.
In general, changing the BCS of a Thoroughbred-type mare from 4 to 6 usually takes about 3-5 pounds of extra concentrate per day for 60 days. For example, if a mare maintains a BCS of 4 with unlimited access to hay/pasture and 3 pounds of concentrate, you will need to feed her 6-8 pounds of concentrate per day to change her body condition to a 6 in about two months. Once she reaches her target body condition, the amount of concentrate can usually be reduced.
Large concentrate intakes have been associated with an increased risk of colic. Therefore, if a mare is somewhat thin in October, adjust the diet immediately to promote weight gain before mid-December, and avoid the very high concentrate intakes.
If a mare is condition scored in October and determined to be too fat, then adjust her diet to reduce calorie intake. For example, Quarter Horse, Arabian, and Morgan mares often can maintain adequate body condition during the fall and winter on good quality forage and a minimal amount of concentrate. To achieve weight loss, create a negative energy balance where calorie intake is less than calorie use. The first step is to reduce concentrate intake or forage quality. Horse owners should also consider ways to increase calorie expenditure, such as placing food and water far apart to encourage exercise.
Once body condition is adjusted in the fall, the broodmare should be fed to maintain body condition while meeting the needs of her stage of pregnancy.
Mares should be given access to good quality hay when pasture availability declines in late fall. Many different types of hay are suitable for broodmares, but the transition in feeding programs is easiest if the nutrient composition of the hay is similar to the nutrient composition of the pasture.
The nutrient composition of hay is influenced by type (legume or grass) and stage of maturity at harvest. In general, legume hays (alfalfa, clover, etc.) are higher in protein and calcium and lower in fiber than grass hays (timothy, orchardgrass, Bermuda grass). Legume hays are usually more palatable as well. Stage of maturity is determined by how mature the plant was at harvest, not the time of year it was harvested.
Many factors affect the amount of hay and concentrate that should be fed to an individual mare. In mid-gestation a mare might be fed 20-25 pounds of hay and 3-8 pounds of concentrate. As she reaches the end of gestation, she might receive between 15-25 pounds of good quality hay and 5-10 pounds of concentrate per day. In most cases the amount of concentrate needed is reduced when the quality of the hay is high.
These are guidelines for mares that normally weigh 1,100-1,300 pounds. Smaller or larger mares will need different feeding programs, and the program should always be adjusted to make sure the mare has a least a moderate body condition. Work with a veterinarian and/or equine nutritionist to establish a feeding program suited to your broodmare's individual needs.
Laurie Lawrence, PhD, is a professor in the department of animal and food sciences at the University of Kentucky.
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Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.