Key Factors Affecting Reproductive Success of Thoroughbred Mares and Stallions on a Commercial Stud Farm

Abstract

To evaluate factors contributing to fertility of thoroughbred mares, data from 3743 oestrous periods of 2385 mares were collected on a large thoroughbred farm in Ireland. Fourteen stallions (mean age 8.3 years; range 4-15 years) had bred 2385 mares (mean age 9.4 years; range 3-24 years). Maiden mares accounted for 12%, mares with a foal at foot for 64%, and barren, slipped or rested mares for 24% of the total. The mean pregnancy rate per cycle was 67.8% (68.6% in year 1 and 66.9% in year 2). Backward stepwise multivariable logistic regression analysis was utilized to develop two models to evaluate mare factors, including mare age, reproductive status, month of foaling, dystocia, month of cover, foal heat, cycle number, treatments, walk-in status and stallion factors including stallion identity, stallion age, shuttle status, time elapsed between covers and high stallion usage on the per cycle pregnancy rate and pregnancy loss. Old age (p < 0.001) and cover within 20 days post-partum (p < 0.003) were associated with lowered pregnancy rates. High mare age (p < 0.05) and barren, slipped or rested reproductive status (p = 0.05) increased the likelihood of pregnancy loss. Uterine inflammation or infection, if appropriately treated, did not affect fertility. Only high usage of stallions (used more than 21 times in previous week) was associated with lowered (p = 0.009) pregnancy rates. However, shuttle stallions were more likely to have increased (p = 0.035) pregnancy survival, perhaps reflecting a bias in stallion selection. In conclusion, mare age exerted the greatest influence on fertility; nonetheless, thoroughbreds can be effectively managed to achieve high reproductive performance in a commercial setting.

Multivariable analysis to determine risk factors associated with early pregnancy loss in thoroughbred broodmares

“…Multivariable analyses investigating reproductive efficiency in thoroughbreds more broadly were conducted in a 2012 study of 1482 New Zealand mares [9] and a 2016 study of 2385 mares in Ireland [18]. These studies looked at pregnancy rates, mating to conception times and pregnancy loss overall (day 15 to term) but did not investigate factors specifically influencing EPL.…”

Advanced mare age impairs the ability of in vitro‐matured oocytes to correctly align chromosomes on the metaphase plate

“…Advanced mare age (in particular beyond 14 years) is associated with a decline in fertility [1][2][3]. This manifests as a lower success of fertilisation in older (81%) than younger mares (96%) [4], and a trebling of the incidence of pregnancy loss between Day 12 and Day 60 in mares aged 18 years or older (30%) compared with mares younger than 12 years (10%) [5][6][7][8].…”

Behavioral Factors Affecting Reproduction in Domestic Horses: Sociobiological Approach

“…Non-genetic, especially environmental and social factors should be routinely involved in studies investigating causes of pregnancy loss besides reproductive health and veterinary aspects. Still it is not the case either in studies of reproductive success [85][86][87] or welfare of breeding horses [88] even after our first report was published [48].…”