Incidence and causes of pregnancy loss after Day 70 of gestation in Thoroughbreds.
Authors: Roach Jessica M, Foote Alastair K, Smith Ken C, Verheyen Kristien L, de Mestre Amanda M
Journal: Equine veterinary journal
Summary
# Pregnancy loss in Thoroughbreds: population-level incidence and aetiologies Late-term pregnancy loss—encompassing abortion, stillbirth and perinatal death—represents a substantial but poorly quantified problem in Thoroughbred breeding, with previous research limited to laboratory submissions that don't reflect true population incidence. Roach and colleagues analysed outcomes from 3,586 pregnancies across eight commercial Thoroughbred studs over five breeding seasons, combining farm records, veterinary documentation and post-mortem examination data to establish robust population-level incidence figures. Overall, 7.3% of Day-70 pregnancies failed to produce a live foal beyond 24 hours post-parturition, with 4.0% lost between Day 70–300 of gestation, 0.3% between Day 301–315, and 1.4% presenting as stillbirth or perinatal death; umbilical cord pathologies emerged as the leading identified cause (1.5%), followed distantly by non-infectious placental disease (0.4%), infectious placentitis and equine herpesvirus (0.3% each), though notably 11.2% of post-mortemed cases yielded no primary diagnosis. These findings provide the first standardised epidemiological framework for late pregnancy loss in the breed and highlight cord-related complications as a key target for prevention strategies, whilst the substantial proportion of cases remaining undiagnosed suggests that further investigation into pathophysiological mechanisms—particularly in cases of unexplained loss—could yield significant clinical dividends for breeding programmes and in-utero management protocols.
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Practical Takeaways
- •Veterinarians managing Thoroughbred breeding programs should counsel owners that approximately 1 in 14 Day-70 pregnancies will fail to produce a live foal, with umbilical cord problems being the leading preventable cause.
- •Submission of fetal/placental tissue for post-mortem examination is critical—only 61% of available tissues were submitted, limiting understanding of causes and prevention strategies.
- •While infectious causes (placentitis, EHV) account for <1% of losses each, umbilical cord pathologies at 1.5% represent a larger target for investigation into management practices that might reduce this incidence.
Key Findings
- •Overall incidence of pregnancy loss producing no live foal at 24 hours post-parturition was 7.3% (95% CI 6.5-8.2) in Thoroughbreds.
- •Umbilical cord-related pathologies were the most commonly diagnosed cause of pregnancy loss at 1.5% incidence (95% CI 1.1-1.9).
- •Between Day 70-300 of gestation, 4.0% (95% CI 3.4-4.7) of pregnancies were lost, with stillbirth/perinatal death accounting for 1.4% (95% CI 1.1-1.9).
- •No primary diagnosis was made in 11.2% of cases that underwent full post-mortem examination, indicating significant diagnostic uncertainty remains.