Reproductive performance of a cohort of Standardbred mares under a commercial breeding system

Abstract

AbstractBackgroundDespite being a large commercial breeding industry, there is little published data on the reproductive success of Standardbred mares.ObjectivesTo quantify the reproductive performance of Standardbred mares under artificial breeding systems in a commercial setting and determine the incidence of early embryonic and other pre‐partum losses.Study designRetrospective cohort study.MethodsData from four commercial farms were collected across four breeding years, and all mares were bred via artificial insemination. A total of 3995 mares contributed 7229 mare years. First‐cycle pregnancy rate (FCPR) and end of season pregnancy rate (SPR) were analysed in mixed‐effects logistic regression models. Time‐to‐conception interval was analysed in a Cox regression model.ResultsThe mean FCPR was 61.4% (confidence interval [CI] 60.3%–62.6%), the mean end of SPR was 84.7% (CI 83.8–85.5%), the mean live foal rate (FR) was 73.1% (CI 72.1%–74.2%). Mares located on‐farm were more probable to be pregnant in terms of both FCPR (odds ratio [OR] 1.168, CI 1.018–1.340, p = 0.026) and SPR (OR 2.026, CI 1.673–2.454, p < 0.001), mares inseminated with thawed–frozen semen were less probable to be pregnant in terms of FCPR (OR 0.598, CI 0.457–0.783, p < 0.001) and SPR (OR 0.479, CI 0.354–0.647, p < 0.001) compared with insemination with fresh‐extended semen. Older mares (14 years and older) were less probable to be pregnant in terms of FCPR (OR 0.795, CI 0.688–0.919, p = 0.002) and SPR (0.435, CI 0.352–0.538, p < 0.001) compared with young mares (3‐ to 8‐year old).Main limitationsRetrospective data relied on accurate record keeping of stud farms and no mare‐treatment or ovulation induction records were available. Live FRs relied mostly on annual foaling returns so fetal/foal deaths may be underrepresented.ConclusionThis study provides substantial baseline data on reproductive performance for Standardbred mares managed under a commercial artificial breeding system.