Relationship between endogenous plasma adrenocorticotropic hormone concentration and reproductive performance in Thoroughbred broodmares.
Authors: Tsuchiya Takeru, Noda Ryusuke, Ikeda Hiroki, Maeda Masaya, Sato Fumio
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary Pituitary pars intermedia dysfunction (PPID) is a well-recognised endocrine condition in older horses, yet its relationship to reproductive failure in broodmares has received limited investigation despite infertility being listed amongst its clinical manifestations. Tsuchiya and colleagues assessed 67 Thoroughbred broodmares presenting with unexplained infertility, stratifying them into three groups based on baseline autumn plasma ACTH concentrations (low <50 pg/mL, intermediate 50–100 pg/mL, high >100 pg/mL) and tracking conception and delivery rates across the subsequent breeding season. Elevated ACTH concentrations correlated significantly with suppressed reproductive outcomes: the high ACTH group achieved conception rates of only 56.5% compared with 77.3–89.5% in the low and intermediate groups, whilst normal delivery rates fell to 43.5% versus 77.2–84.2%. Plasma cortisol concentrations also increased proportionally with ACTH levels, confirming pituitary axis activation in the elevated groups. These findings suggest that PPID may account for a meaningful proportion of idiopathic infertility cases in breeding mares, with screening plasma ACTH concentrations offering a straightforward diagnostic approach to identify affected animals early. For practitioners managing subfertile broodmares, incorporation of ACTH testing into the diagnostic workup—particularly in older mares—could facilitate earlier intervention and materially improve reproductive success rates through targeted endocrine management.
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Practical Takeaways
- •Measure baseline endogenous plasma ACTH concentrations in Thoroughbred broodmares presenting with infertility of unknown cause, as elevated ACTH (>100 pg/mL) is strongly associated with poor conception and delivery rates
- •Mares with high ACTH levels have less than half the normal delivery rate (43.5% vs. 77-84%), making early PPID diagnosis and treatment potentially critical for maintaining breeding viability
- •Use Equine Endocrinology Group reference ranges (low <50, intermediate 50-100, high >100 pg/mL) to stratify reproductive risk and counsel owners on prognosis and intervention options
Key Findings
- •High endogenous plasma ACTH concentration (>100 pg/mL) was associated with significantly lower conception rates (56.5%) compared to low (<50 pg/mL: 77.3%) and intermediate (50-100 pg/mL: 89.5%) groups (P = 0.02)
- •Normal delivery rates were significantly reduced in the high ACTH group (43.5%) versus low (77.2%) and intermediate (84.2%) groups (P = 0.008)
- •Plasma cortisol concentrations were significantly elevated in intermediate and high ACTH groups compared to the low ACTH group (P < 0.001)
- •Screening plasma ACTH concentrations in infertile broodmares can identify PPID and guide early treatment to improve reproductive outcomes