All broodmares should have their body condition assessed regularly, as mares in good body condition have a reservoir of stored fat that can be used during cold winter weather. Good body condition helps barren and maiden mares establish normal cycles sooner in the breeding season and results in higher conception rates. Similarly, mares in good body condition at foaling are easier to rebreed than thin mares.
Owners can usually assess a horse's body condition by evaluating the amount of fat deposited on the ribs, along the neck and spine, and behind the shoulder. The typical scoring system uses a 1 to 9 scale, where a horse with a score of 1 is emaciated and 9 is obese. A horse with a condition score of 5 is considered to have "moderate" body condition. Mares that enter the breeding season with a condition score below 5 have reduced reproductive efficiency. Therefore, the target body condition score for broodmares is at least 5. While there is no advantage to a mare having a very high score (being very fat), if she has a score of 6 in late fall she will have a small reserve of fat during winter when she will be burning extra calories to stay warm.
Horses with body condition scores between 5 and 6 have ribs that can be felt easily, but that are not visible. In addition, these horses have enough fat cover over their topline that the loin area is relatively flat. Their necks are not thin and blend smoothly into the shoulder. A horse with a score higher than 7 has ribs that are difficult to feel and so much fat along the spine that there is a deep crease in the loin area. On the other hand, if the spine is visible along the loin area and the ribs are also visible, then the body condition score would be closer to a 4. If more of the mare's bony structures are visible (e.g., the shoulder or hip bones are prominent) then the body condition score would be below a 4.
Many mares that nursed a foal during the summer and early fall as well as mares used for strenuous competitive activities during the summer (racing, endurance competition, polo, etc.) often enter the fall with condition scores below 5. These horses will need to consume extra calories in the fall to ensure they are in good body condition for the next breeding and foaling season.
Mares that have been grazing abundant, high-quality pasture all summer and fall might have body condition scores above 7. Although high condition scores have not been shown to negatively affect reproduction, they might increase a mare's risk for limb and hoof problems, including laminitis. If a horse is overweight, winter is a good time for weight loss because the pasture is less nutritious and the cold weather increases calorie use.
Pasture and Hay
As pasture quality and quantity decline in late fall, owners should supplement mares' forage intake with hay. Some horse managers in Central Kentucky begin feeding hay to pastured mares beginning Nov. 1, but make a decision based on the condition of your individual mares and pasture. If the mares are losing body condition, the nutrients available to them are likely insufficient. Even if the mares seem to be maintaining body condition but the pasture is showing signs of overgrazing, it is probably time to offer hay. Providing hay in the fall will serve two purposes: First, it ensures mares will have enough to eat; and second, it might reduce overgrazing of the pasture. Overgrazing in the fall can weaken the plants, thus reducing their vigor the next spring and summer. Overgrazing can also allow more weeds to invade the pasture.
The best way to evaluate whether pastured mares need hay is to put some in the pasture. If the horses ignore the hay, then the pasture is probably meeting their forage needs. If they eat some but not all of the hay, then the amount of hay fed can be reduced until the amount that remains at the next feeding is small. If the horses devour the hay rapidly, the pasture quality is clearly declining and the horses need hay.
Many types of hay are acceptable for broodmares, but the main selection characteristics should be safety and nutrition. Most tall fescue in the southeastern United States is infected with a fungal endophyte that can negatively affect mares in late gestation. Unless tall fescue hay has been tested and is known to be endophyte-free, it should not be used for mares, especially pregnant mares. Any hay that is fed to horses should also be free of toxic weeds, dust, and mold.
Legume hays (e.g., alfalfa and clover) are higher in nutrients than most grass hays (timothy, orchardgrass, etc.). In a recent study conducted at the University of Kentucky (UK), Thoroughbred mares in mid and late gestation were able to eat enough good-quality alfalfa hay to meet their protein requirements. Mares fed timothy hay were able to eat enough hay to meet their protein requirements in mid-gestation, but not in late gestation. When applied to practical feeding situations, these results mean horses fed good-quality alfalfa hay will require less concentrate (sweet feed or pellets) than horses fed timothy hay.
In addition to considering the type of hay to use, a broodmare owner might want to estimate how much hay he or she will need to provide during the fall and winter. In the UK study mares consumed about 2-2.25 pounds of hay for each 100 pounds of body weight. So a medium-sized Thoroughbred mare (1,250 pounds) would consume about 25-28 pounds of hay daily. Remember that this figure represents the amount of hay consumed, not the amount fed. There will always be some wasted hay, so the amount fed should be slightly greater than the amount to be consumed. However, the mares in the study received only a small amount of concentrate each day, and mares fed greater amounts of concentrate would need less hay. If hay is fed at 30 pounds/horse/day from Nov. 1 through March 30, then a little more than two tons of hay will be needed to feed the medium-sized mare over this period. If the hay feeding period is longer or shorter, or the mare is expected to eat more or less hay, then the total amount of hay would change.
Concentrates and Supplement Pellets
In addition to pasture and/or hay, broodmares are usually fed either a commercially manufactured concentrate or supplement pellet (sometimes called a balancer pellet). The term "concentrate" refers to a feed that is a concentrated source of calories. Common concentrates such as oats, corn, and other cereal grains are good sources of calories but they are low in calcium and other necessary nutrients. Commercially manufactured concentrates usually include cereal grains, but they also contain additional nutrients. If a concentrate is formulated for a broodmare, the level of nutrient supplementation will be targeted to meet her needs. Concentrates are added when the forage portion of the diet does not provide enough calories to meet a mare's needs. Most Thoroughbred-type mares should receive 5-10 pounds of concentrate in late gestation. Mares from small, thrifty breeds will usually be fed less concentrate in late gestation.
Supplement pellets are concentrated sources of vitamins, minerals, and sometimes protein. They are fed in small amounts (usually 1-2 pounds per day) when the pasture or hay provides all the calories a mare needs. For example, if a mare can maintain a condition score of 6 on pasture or hay alone, then she does not need the extra calories provided by a concentrate. But, she does need many of the minerals provided in the supplement pellet. Supplement pellets are not needed if a mare is getting at least 4 pounds of a commercially manufactured broodmare concentrate. However, a supplement pellet can be combined with a plain cereal grain (such as oats) if an owner prefers not to use a commercially manufactured feed.
Laurie Lawrence, PhD, a professor in the Department of Animal and Food Sciences at the University of Kentucky, provided this information.
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Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.