STRESS AND GLYCEMIC RESPONSES TO POSTPRANDIAL INTERVAL AND FEED COMPONENTS IN EXERCISING HORSES

Six Thoroughbred geldings were used in a Latin square design to determ ine the effects of three feeding regimens and two postprandial interva ls on stress parameters during rest, exercise, and recovery. Each hors e was randomly assigned to one of six treatments on six sampling days. The three feeding regimens consisted of a fasting regimen in which no feed was offered, or an isoenergetic (4.1 Meal DE) meal of either cor n or alfalfa. One or 4 h after feeding, a standardized exercise test ( SET) was imposed on all horses. The SET consisted of three 10-min peri ods each of saddling, walking to the arena, and warm-up (walking and t rotting), followed by three bouts of progressively more intense gallop ing at heart rates of 130-140 (10 min), 150-160 (10 min), and 170-180 bpm (5 min), respectively. Blood was sampled via jugular catheters fro m 0630 to 1500, including the 55-min SET. Analysis of variance by repe ated measures within either the 1- or 4-h protocol showed no differenc es between dietary treatments for glucose concentration; differences d ue to sampling time were shown for concentrations of glucose, lactate, cortisol, alpha(1)-acid glycoproteins (AGP), and the neutrophil to ly mphocyte ratio (N:L). In both the 1- and 4-h protocols, glucose concen trations decreased precipitously in corn-fed horses at the onset of th e SET, but rebounded at the termination of the galloping. Plasma gluco se concentrations in fasting and alfalfa-fed horses decreased slightly and then gradually increased throughout the SET. Serum cortisol and p lasma lactate concentrations did not differ (P>.05) between dietary tr eatments, but increased concentrations were detected during the SET in both the 1- and 4-h protocols, The AGP concentration and N:L did not differ (P>.05) due to dietary treatments; however, AGP concentrations marginally increased (P<.10) from prefeeding to early recovery during the 1-h but not the 4-h protocol. The N:L increased (P<.05) in respons e to exercise; elevated values were detected in early recovery.