Reproductive efficiency of Thoroughbred mares under Indian subtropical conditions: A retrospective survey over 7 years

Service records of 253 mares (1181 mare-years) spanning over 7 consecutive years, from nine organized Thoroughbred stud farms, situated in the subtropical northwestern India were retrospectively analyzed to assess their reproductive performance. The overall per cycle pregnancy rate at Day 16 and overall foaling rates were 50.30% and 68.95%, respectively, and were significantly higher in mares aged 3–7 years than ≥18 years old mares. The late embryonic losses (9.86%) that occurred between Days 16 and 39 post-ovulation contributed more than 50% of the overall detected pregnancy losses (19.11%). The overall percent detected pregnancy losses were lower in mares at ages 3–7 years compared to those at ages ≥18 years (14.78% vs. 46.43%, respectively; P < 0.0001). Chronic barren and habitual aborter mares tended to affect reproductive efficiency of mares. Fifty percent of the mares that experienced ≥2 consecutive abortions or barren years, again stayed aborted or barren in the next seasons, respectively. No effect of numbers of matings per oestrus was observed on overall fertility. Neither the induction of oestrus nor ovulation by exogenous hormonal treatment had any effect on most of the analyzed reproductive parameters. Regarding breeding month or years, the reproductive efficiency did not differ significantly. The incidence of multiple pregnancies was 5.40% and percent late embryonic loses were higher (P = 0.0016) in twin (21.98%) than singleton (8.64%) pregnancies. In conclusion, comparatively lower fertility rates were recorded in Thoroughbred mares bred under Indian subtropical climatic conditions than those reported from temperate regions that might be due to difference in breeding management rather than prevailing environment.