Optimal Body Condition Scores for Breeding Mares

Descriptions such as “ribby” and “pudgy” are vague. One horseman may characterize a mare as “heavy,” while another would describe her as “fatter than a county fair hog.” By these descriptions, however, neither horseman may know just how fat that mare truly is!

Since the mid-1980s, nutritionists, farm managers, veterinarians, and animal-welfare workers have employed a universal method of measuring weight and fat distribution. This process, called body condition scoring, has become a valuable management tool on breeding farms worldwide. By visually and manually evaluating certain anatomical regions (namely the neck, shoulder, withers, ribcage, backbone, and tailhead), horsemen assign horses and ponies a score between 1 and 9, with 1 designating extreme emaciation and 9 indicating out-and-out obesity.

Broodmares are typically maintained in the condition score range of 5-7, with some individuals obviously falling below or above that range.

Descriptions of these three body condition scores are given below.

Score and description

5, Moderate — Back is flat (no crease or ridge); ribs not visually distinguishable, but are easily felt; fat around tailhead beginning to feel spongy; withers are rounded; shoulders and neck blend smoothly into the body

6, Moderately Fleshy — Might have slight crease down back; some fat cover over the ribs, along the sides of the withers, behind shoulders, and along the side of the neck; fat around tailhead is soft

7, Fleshy — Might have crease down back; individual ribs can be felt but noticeable fat deposition between the ribs; fat deposited along withers, behind shoulders, and along neck

Numerous scientific trials have demonstrated the relationship between body condition and fertility. One field trial followed 927 mares from the beginning of the breeding season through pregnancy confirmation. Mares were given a body condition score at the onset of the season, and based on that assessment, they were divided into three subsets: mares with a body condition score of less than 5 (158); mares with a body condition score of 5, 6, or 7 (667 mares); and mares with a body condition score greater than 7 (102 mares).

Mares with a low body condition score were least likely to conceive. Of these 158 mares, only 71% achieved pregnancy. In the two remaining groups, pregnancy rates were markedly higher, 92% in mares with a body condition score of 5, 6, or 7, and 96% in mares with a body condition score greater than 7.

In addition to pregnancy rates, mares with low body condition scores required nearly 2.8 heat cycles per conception, while more well-conditioned mares required only 1.4 heat cycles per conception. If mares are in low body weight at the onset of breeding season, first ovulation may lag three to four weeks behind that of mares carrying more weight. This is meaningful because breeding managers bank on getting open or maiden mares in foal early in the season prior to the influx of foaling mares.

Early fetal survival is also affected by body condition of the mare. Losses are significantly greater in mares with body condition scores of 4 or less. Environmental and physiological stresses will affect the body condition of mares as breeding season nears. Competition for food by herdmates or scarcity of feed in winter may lead to thinness. Moreover, lactation can easily deplete energy stores of mares, leaving them with reduced body condition and breeding efficiency.

Some horsemen feel that mares maintained at condition scores of 6 or higher will experience foaling complications. Extensive research has shown that mares in moderately fleshy condition or heavier (a score of 7 or higher) did not encounter problems often associated with obesity including prolonged pregnancy and decreased foal size or vitality at birth.

Though every mare should be managed individually with her best interests in mind, a few general recommendations can be made.

• Maintain open or maiden mares at a body condition score of 6 or 7 leading up to the breeding season. For pregnant mares that will be lactating in late winter or spring, a condition score of 7 or 7.5 is ideal. Keeping mares at condition scores higher than 7.5 does not enhance fertility and is not wise from an economic standpoint.
• Evaluating the body condition of pregnant mares may become more difficult during late gestation, as the combined weight of the fetus and amniotic fluid may pull the skin tightly over the vertebral column and ribcage. Therefore, it’s best to place emphasis on other key areas: along the withers, behind the shoulder, and around the tailhead.
• Do not rely completely on visual appraisal to assess body condition. By palpating certain areas, evaluators can more accurately judge body condition. For example, ribs that are not visible may or may not be felt easily. Palpation is particularly important in winter when mares likely have winter coats. If possible, have the same person evaluate condition on a monthly schedule, as this will ensure a degree of consistency.