Body condition and reproductive efficiency of mares

Includes bibliographical references (leaves 96-101)Thirty-two mares were fed to foal in fat (treatments H-H and H-L) or thin (treatments L-L and L-H) condition. Caloric intake was changed at parturition. Mares were fed to maintain foaling weight and condition (treatments H-H and L-L), lose weight and condition (treatment H-L) or gain weight and condition (treatment L-H) during the first 90 days of lactation. Pregnancy rate was lower (P < .05) in the L-L mares (50%) than in the other groups (100%). Maintenance of pregnancy was also reduced (P < .05) in the L-L group of mares (25%) when compared with the H-H and L-H mares (100%) and the H-L mares (88%). Foal growth at 90 days of age was similar in all treatments. A condition scoring system was developed to compare horses based on the amount of stored fat in their bodies. This system was a more accurate indicator of body fat content than weight, height, heartgirth, weight/height and heartgirth/height. A field study was conducted using the condition score system to evaluate the relationship between body condition and reproductive efficiency of mares. A total of 927 mares from four ranches were utilized. Pregnancy rate was lower (P < .05) and the number of cycles per conception was higher (P < .05) in mares entering the breeding season or foaling in thin condition (condition score 4.5 or below) when compared with fatter mares. In addition, the onset of estrus and the transition ovulation were delayed (P < .05) in barren and maiden mares entering the breeding season in thin condition. Breeding efficiency was highest when mares entered the breeding season or foaled at a condition score of 5.0 or above. Initial excess stores of body fat did not adversely affect fertility