Professor and Director, Horse Science program Middle Tennessee State University Murfreesboro, TN, United States
Abstract:
Background: The thyrotropin releasing hormone (TRH) stimulation test is a dynamic test for PPID that has been described as a sensitive diagnostic test for PPID. Published studies have reported the feeding effects of hay vs fasting on TRH diagnostic testing results, but not the evaluation of TRH testing results in grain-fed vs hay-only in PPID positive and negative horses. Hypothesis/
Objective: Feeding grain would not affect basal T0-ACTH or T10-ACTH results after TRH-stimulation. Animals: Six PPID-positive and six PPID-negative horses of known status were used.
Methods: The protocol was approved by the Institutional Animal Care and Use Committee. All horses were fed prairie grass hay as basal diet, or hay plus pelleted grain concentrate meeting NRC requirements, in a crossover design with a 2-week testing interval. Previous work in this laboratory found consistent basal ACTH and TRH-stimulation results at 2-week intervals. Two hours after eating hay-only or the grain-fed diet, blood samples were collected before and 10 minutes after 1 mg TRH administered i.v. A mixed model with repeated measures analyzed the effect of grain feeding on T0-ACTH, T10-ACTH, and the percent increase of ACTH after TRH-stimulation.
Results: Compared to hay only, grain feeding did not affect T0-ACTH (P=0.22), T10-ACTH (P=0.09), or the percent increase in ACTH (P=0.18) in PPID-negative or PPID-positive horses. No change in PPID classification was observed comparing grain-fed vs hay-only in PPID-positive or PPID-negative horses. Conclusions and clinical importance: Based on these results, horses may be fed grain prior to TRH stimulation testing for PPID.
