Assessment of baseline adrenocorticotropic hormone and insulin concentrations in healthy horses in Saskatchewan over a 1-year period.

Abstract

BACKGROUND: Endocrine disorders in horses, such as pituitary pars intermedia dysfunction and equine metabolic syndrome, rely on hormone testing for diagnosis, but seasonal and regional variabilities highlight the need for locally generated data. HYPOTHESIS/OBJECTIVES: To characterize monthly blood concentrations of ACTH and insulin over 1 year in healthy horses in Saskatchewan. A secondary objective was to assess the association between these outcomes and the following factors: sex, age, breed, pregnancy status, level of exercise, body condition score, and cresty neck score. ANIMALS: Sixty-eight clinically healthy, client- or university-owned horses. METHODS: Prospective, observational study. Inclusion criteria: normal physical exams, no travel outside Saskatchewan, no ongoing endocrine or metabolic illness. Samples were collected monthly for 12 months. Blood concentrations of ACTH and insulin were determined by a chemiluminescence assay and associations with the explanatory variables were assessed using generalized estimating equations and generalized linear models. RESULTS: The concentration of ACTH varied by age and month, with older horses showing greater seasonal fluctuations. Maximum ACTH concentration peaked in late summer and early fall, with the older horses and certain breeds showing higher concentrations. Insulin concentrations were highest in August and lowest in December, and consistently higher in Warmbloods than Quarter Horses. CONCLUSIONS AND CLINICAL IMPORTANCE: Our findings reveal month- and age-related effects on ACTH concentration, and month- and breed-related effects on insulin concentration in healthy horses. These findings support the need to consider temporal and signalment factors when interpreting endocrine test results.