Relationship between endogenous plasma adrenocorticotropic hormone concentration and reproductive performance in Thoroughbred broodmares

Background Pituitary pars intermedia dysfunction (PPID) is an endocrine disorder the clinical signs of which include infertility, but few reports have examined the relationship between PPID and reproductive performance in broodmares. Hypothesis/Objective Broodmares with infertility of unknown etiology were screened for PPID using baseline endogenous plasma ACTH concentrations, and its relationship with subsequent reproductive performance was analyzed. Animals Sixty‐seven Thoroughbred broodmares. Methods Adrenocorticotropic hormone concentrations were measured in autumn. The broodmares were divided into 3 groups based on endogenous plasma ACTH concentration (low, 100 pg/mL) as recommended by the Equine Endocrinology Group. We compared these results with those of other blood tests, clinical examinations, subsequent conception, and frequency of normal delivery. Results The numbers of horses per group (percentage) were 22 (32.8%), 20 (29.9%), and 25 (37.3%). The mean ± SD ages (years) were 11.1 ± 3.4, 12.1 ± 4.5, and 13.0 ± 4.3, with no significant difference among groups. Mean ± SD plasma cortisol concentrations (μg/dL) were 4.0 ± 1.6, 7.1 ± 1.4, and 7.6 ± 1.9, with the intermediate and high ACTH groups having significantly higher results than the low ACTH group (P