Endocrinologic, hematologic, and heart rate changes in swimming horses

Two identical experiments, using Standardbred and Thoroughbred horses (experiment A, n = 31; experiment B, n = 17) on a swimming regimen, were performed 1 week apart to evaluate short-term heart rate, hematologic, and endocrinologic changes. Horses were placed in 4 categories based on duration of swimming (1 to 5, greater than 5 to 10, greater than 10 to 15, and greater than 15 minutes). Heart rate, PCV, and plasma concentrations of total protein, cortisol triiodothyronine, thyroxine, insulin, and glucose of each horse were evaluated before, immediately after, and 1 hour after swimming. For experiment A, there was a main effect of time of sampling on PCV, total protein, triiodothyronine, thyroxine, and insulin. There was a main effect of duration of swimming on insulin concentration and an interaction of duration of swimming and time of blood collection on heart rate and cortisol concentration. For experiment B, there was a main effect of time of blood collection on all the variables except glucose.