143 Factors affecting pregnancy rates on a commercial Thoroughbred breeding farm: A retrospective analysis of breeding shed data

Abstract

Understanding the factors that affect per cover pregnancy rates on commercial breeding farms is important for efficient operation and improving breeding management. Breeding shed records for 9 seasons (2009–2017) from a commercial Thoroughbred breeding farm were used to evaluate factors influencing reproductive success. Observations of individual covers (n = 10,156) were recorded by the manager and trained staff and included information on mating demographics; cover and semen characteristics; and mare conformation and behavior. Incomplete records were removed from the data set providing 8,843 observations. The effect of each factor on pregnancy rate was analyzed using a generalized linear model and binomial distribution. Per cover pregnancy rate (PR) was different (P < 0.001) between stallions (n = 20) and ranged from 53 to 70% (mean average = 63%). PR was lower (P < 0.001) in barren mares compared with foaling and maiden mares; July covers (P < 0.001) compared with all other months; and when dismount samples contained urine (P < 0.001). Mares scoring 0 or 1 (on a 0–4 tease scale) were less likely (P < 0.05) to conceive than mares showing stronger estrous behaviors when teased before mating with LS means of 40.4, 54.4, 62.2, 62.6 and 65.9 % PR for tease scoresof 0, 1, 2, 3 and 4 respectively. There was a trend (P = 0.08) for lower PR in mares requiring tranquilization (57.1%) compared with non-tranquilized mares (62%) supporting the importance of estrous behavior for successful mating. Insemination post live cover was performed 15% of the time due to either a large dismount sample or per owner request, however there was no difference in PR. Pregnancy rate was higher (P < 0.05) in mares with vulva sutures (63.5%) or having acceptable vulvar conformation without sutures (64.1 %) compared with poor vulva conformation without sutures (59.3%). Mating quality assessed by a subjective cover grade (A, B+, B, B-, C) positively influenced PR (P < 0.001) while other factors including: number of mounts, number of semen pulses, time of day and presence of RBC and WBC in the dismount sample had no effect on PR, although there was a trend (P < 0.08) for lower PR when WBCs were noted in the dismount samples. Maintaining detailed breeding shed records can provide managers with useful information which could be used in making management decisions.