2017 ACVIM Forum Research Abstract Program

Seventeen horses meeting the study's inclusion criteria were tested for PPID, using endogenous ACTH plasma concentrations and the thyrotropin releasing hormone (TRH) stimulation test. The study included six healthy horses (group 1: plasma ACTH concentrations < 110 pg/mL post TRH administration) and 6 horses with PPID (group 2: plasma ACTH concentrations above seasonal reference ranges or >110 pg/mL post TRH administration). All 12 subjects were stabled in box stalls with free choice access to grass hay and water for the duration of the study. The study was conducted in accordance of the University of Missouri's Animal Care and Use Committee and between February to July. After a 48-hour acclimation period, blood samples were collected to measure baseline ACTH and cortisol concentrations in all horses. Dexamethasone (0.05 mg/kg) was subsequently administered IV once. For the next 48 hours, ACTH and cortisol were measured every 6 hours. Repeated measures ANOVA analysis followed by post hoc testing determined significant effects of dexamethasone treatment on ACTH and cortisol concentrations over time in both groups of horses and compared differences between groups.