(E54) Endocrine Disorder Classifications and Clinical Sign Frequencies using Static and Dynamic Testing Among Horse Breeds

Background
Rates of endocrine disorders vary among breeds, though less is known about endocrine-associated clinical sign (EACS) frequencies among breeds.

Hypothesis/Objectives
The objective of this research is to evaluate PPID classification and EACS frequencies for different breeds using pre- and post-TRH stimulation ACTH values.

Animals
Arabians (n=194), Thoroughbreds (n=217), and Warmbloods (n=371), ages 4 to 38, with EACS were tested for endocrine disorders using spring TRH stimulation testing by their veterinarian from 2016-2023.

Methods
Horses were considered PPID positive if spring basal ACTH levels were >35 pg/mL (2016-2020) or >30 pg/mL (2021-2023), or spring post-TRH-stimulated ACTH levels were >110 pg/mL. EACS rates were determined per PPID classification using pre- and post-TRH-stimulation ACTH levels. PPID rates were analyzed using two-way ANOVA; odds ratios were calculated per EACS.

Results
PPID classification among breeds using pre-and post-TRH stimulation ACTH values were similar (p>0.9999). Using basal ACTH values, 21-36 percent of horses were classified as PPID positive, increasing to 36-72 percent when post-TRH stimulation ACTH values were utilized (p< 0.0001). Using post-TRH stimulation ACTH levels for PPID classification instead of basal ACTH levels reclassified 18-39 percent of horses from PPID negative to PPID positive, and reclassified 3-5 percent from PPID positive to PPID negative (p=0.0465). EACS frequencies significantly varied among breeds depending on pre- or post-TRH stimulation levels (p< 0.0001). No odds ratios reached statistical significance (α=0.05; p=0.1176->0.9999; 95% CI included 1).

Conclusions and Clinical Importance
Different EACS frequencies were observed among these breeds, revealing opportunities to refine identification strategies for candidates for dynamic ACTH testing.