Reproductive performance measures among Thoroughbred mares in central Kentucky, during the 2004 mating season.
Authors: Bosh K A, Powell D, Shelton B, Zent W
Journal: Equine veterinary journal
Summary
# Reproductive Performance in Thoroughbred Mares: A Central Kentucky Analysis Understanding how management decisions influence reproductive outcomes remains critical for optimising farm efficiency, yet few studies have quantified these relationships at scale. Bosch and colleagues tracked 1,011 mares across 13 central Kentucky farms throughout the 2004 mating season and into the 2005 foaling period, collecting detailed reproductive records alongside farm management practices via manager interviews to examine how mare age, category (maiden, foaling, or barren) and stallion workload affected pregnancy establishment and maintenance. Season pregnancy rates reached 92.1% by day 15 post-mating and 89.3% by day 40, with a live foal rate of 78.3%, though per-cycle conception rates were considerably lower at 64.0% and 58.3% respectively—highlighting that multiple cycles were frequently necessary. Notably, stallions with larger book sizes maintained fertility comparable to those with smaller workloads, whilst mare age emerged as the dominant factor influencing pregnancy success and foal production; the average mating season extended 36.5 days, with potential for reduction through strategic scheduling. These findings provide equine professionals with actionable benchmarks for evaluating mare management protocols and identifying individuals whose reproductive performance warrants culling decisions, whilst demonstrating that extending mating seasons unnecessarily may reflect suboptimal timing of first matings rather than true subfertility.
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Practical Takeaways
- •Optimize mating season scheduling by prioritizing maiden and barren mares early in the season and waiting for appropriate uterine involution in foaling mares to reduce overall season length and improve efficiency
- •Focus management attention on older mares as they show reduced efficiency in becoming pregnant, maintaining pregnancy, and producing live foals compared to younger mares
- •Monitor stallion workload reassurance—large book sizes do not impair fertility, so reproductive underperformance should be attributed to other farm management factors
Key Findings
- •Per season pregnancy rates were 92.1% at Day 15 post-mating and 89.3% at Day 40, with live foal rate of 78.3%
- •Mare age significantly impacted efficiency of pregnancy establishment, maintenance, and live foal production
- •Stallion book size had no significant association with reproductive performance outcomes
- •Mating season interval averaged 36.5 ± 26.1 days and could be reduced by scheduling maiden and barren mares early and foaling mares after uterine involution