Physiological responses to training and racing in two-year-old quarter horses

Summary Beginning at approximately 18 mo of age, fifty-three Quarter Horses were trained to ride, conditioned and run in nine match races with three each at 274 m, 320 m and 366 m. As part of a companion study, the horses were fed varying amounts of Sodium Zeolite A. During the last long slow distance (LSD) workout, the last LSD with sprints workout prior to racing, and each race, blood samples were collected and heart rates (HR), respiration rates (RR) and rectal temperatures (RT) were measured at rest, after the warm-up, and at 1, 2, 5, 10, 20, 30, 60 and 120 min of recovery. Blood samples were analyzed for packed cell volume (PCV) and plasma ionized calcium (Ca++), sodium (Na+), potassium (K+), lactate (LA − ) and glucose (GLU) concentrations. Data were analyzed by ANOVA using the general linear model of SAS appropriate for repeated measures and Scheffe's multiple comparison test to compare diet, race and sample (time) effects. Results were considered significant at P The horses were able to run increasingly longer races without corresponding changes in HR, PCV or plasma Na+, K+, Ca++, LA - or GLU concentrations. The warm-up elicited an average HR of 163 beats/min, yet HR during and immediately after the races did not go as high as commonly observed in Thoroughbred racehorses running longer distances. Respiration rate and RT were higher during recovery from the longer races in response to increased metabolically generated heat.