Relationship between body fat and body condition score and their effects on estrous cycles of the Standardbred maiden mare.

Abstract: Standardbred maiden mares are generally stressed and in poor physical condition because of their incorrect management at the end of their racing careers. The purpose of this study was to identify an objective assessment that, similar to body condition score (BCS) determination, is easy to measure and able to confirm or improve fattening status assessment, as well as to ascertain whether a relationship with reproduction efficiency exists in subjects destined for a first-time insemination program. The authors assessed 29 Standardbred maiden mares (7 +/- 2 years old) during the breeding season. On January 15 (day 0), the same operator performed the following on all subjects: the first gynecological and ultrasound examination, a BCS assessment (range 0 to 5), and an adiposity objective assessment (i.e., measurement of fat thickness by ultrasound scan). At day 0, all mares were in seasonal anestrous. On ovulation day, all subjects exited the study. Both techniques were shown to be significantly and reciprocally correlated (r = 0.976; P < 0.01) to the first seasonal ovulation in maiden mares (-0.772 and -0.805, respectively, for fat thickness and BCS; P < 0.01). Based on the results obtained, regression equations for the prediction of days to the first seasonal ovulation (y) were created. The best predictive equation was the following: y = 26.714x(3) - 202.44x(2) + 446.04x - 195.65 (R(2) = 0.783; SE = 17 d; P0.01), with an independent BCS variable. In conclusion, this study suggests that increasing the plane of nutrition (i.e., flushing), starting approximately 3 weeks before the breeding season, stimulates ovarian activity in stressed maiden mares.