Influence of pituitary pars intermedia dysfunction on reproductive performance in Thoroughbred mares.
Authors: Murase H, Wachi S, Matsuyama R, Makita K, Sato F
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Pituitary pars intermedia dysfunction (PPID) is a common age-related condition in older horses, but its specific effects on mare fertility have remained unclear because aging itself impacts reproductive performance. Murase and colleagues investigated 332 Thoroughbred mares aged 10–20 years across Japanese breeding farms, classifying them by plasma adrenocorticotropic hormone concentration to establish PPID status and tracking reproductive outcomes over two breeding seasons. Crucially, they found that whilst PPID prevalence was 9%, the condition exerts a disproportionate negative effect on pregnancy rates *in combination with advancing age*—mares with both PPID and older age showed significantly steeper declines in fertility than age-matched unaffected counterparts. When PPID-positive mares were subsequently treated (n=15), pregnancy rates reached 80%, compared to just 44% in untreated mares, though this difference did not reach statistical significance, likely due to small sample size. For practitioners managing breeding mares over ten years old, these findings suggest that PPID screening becomes increasingly relevant to reproductive success, and treatment warrants serious consideration given the substantial numerical improvement in conception rates, particularly as mares age.
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Practical Takeaways
- •Screen older Thoroughbred mares (10+ years) for PPID if experiencing declining fertility, as the condition accelerates age-related reproductive decline
- •Treatment of PPID appears to improve pregnancy outcomes in mares (80% vs 44% pregnancy rates), warranting consideration in breeding programs despite statistical limitations
- •Age should be factored into fertility assessments in older mares, as PPID's impact on reproduction is magnified with advancing age
Key Findings
- •PPID prevalence was 9.04% in Thoroughbred mares aged 10-20 years
- •PPID mares showed greater age-related decline in pregnancy rates compared to non-PPID mares (AOR 0.49, p=0.02)
- •Treated PPID mares had 80% pregnancy rate versus 44.4% in untreated PPID mares, though difference was not statistically significant (p=0.10)
- •No significant differences in prolactin concentrations were observed among PPID status groups