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Multivariable analysis to determine risk factors associated with abortion in mares

Roach, Jessica; Arango-Sabogal; Smith, Ken; Foote; Verheyen; de Mestre, Mandi


Jessica Roach


Ken Smith



Mandi de Mestre


Risk factors associated with equine reproductive efficiency have been identified along with those associated specifically with early pregnancy loss (EPL). In contrast, no studies have reported risk factors associated with abortion (loss between day 70 and 300 post-cover). Given the causes of abortion differ to those of EPL, likely too will the risk factors. A retrospective cohort study was carried out to identify risk factors associated with abortion in UK and Irish based Thoroughbreds, collecting data on 20 exposure variables over a five-year period. A generalized linear mixed model was utilized to evaluate the associations between exposure variables and abortion, with clustering of observations accounted for at the mare and farm level. Variables with a likelihood ratio test (LRT) p value <0.2 were entered into the model in a forward stepwise approach. Pregnancy outcome was available on 4,439 pregnancies from 2,510 mares. Having had two or more prior abortions (odds ratio (OR) 7.91, 95% confidence interval (CI) 2.86, 21.88), conceiving on the second or subsequent covered estrous cycle (OR 1.84, 95% CI 1.22, 2.78) and conceiving multiple conceptuses (OR 1.68, 95% CI 1.02, 2.76) were associated with an increased risk of abortion compared to null parous, first estrous cycle covers and singleton conceptions respectively. Increasing paternal age (OR 0.95, 95% CI 0.90, 0.99) was associated with a decreasing risk of abortion. Mare and farm variance were not significant in the final model, LRT p=0.43. These findings provide evidence-based data to inform Thoroughbred breeding management practices to help mitigate abortion risk.


Roach, J., Arango-Sabogal, Smith, K., Foote, Verheyen, & de Mestre, M. (2022). Multivariable analysis to determine risk factors associated with abortion in mares. Reproduction and Fertility,

Journal Article Type Article
Acceptance Date Nov 14, 2022
Online Publication Date Nov 14, 2022
Publication Date Dec 7, 2022
Deposit Date May 11, 2023
Publicly Available Date May 12, 2023
Print ISSN 2633-8386
Publisher BioScientifica
Peer Reviewed Peer Reviewed


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