Acid-base and electrolyte effects of shortening steeplechase in a three-day-event.

This study was designed to characterise the acid-base and electrolyte effects of shortening the distance required during steeplechase (Phase B) in the face of hot and humid weather conditions during a treadmill-simulated Speed and Endurance test. Eight conditioned Thoroughbred horses underwent 3 randomised permutations of a standardised exercise test on a high speed treadmill. Each test consisted of trotting at 3.7 m/s for 10 min (Phase A); galloping at 11 m/s (Phase B) for 4 (cool laboratory conditions), 3 (hot and humid), or 2 (hot and humid) min; trotting at 3.7 m/s for 30 min (Phase C); and walking at 1.8 m/s for 10 min (Phase X). The treadmill slope was 4% for trotting and galloping and 0% for walking. Cool versus hot and humid conditions were 20 degrees C and 50-60% relative humidity vs. 26-28 degrees C and 80-85% relative humidity, respectively. Pulmonary artery blood samples were obtained at rest prior to exercise (Rest); at the end of Phases A (A10) and B (B2-4); at 10 (C10), 20 (C20) and 30 (C30) min through Phase C; and at 5 min into Phase X (X5). Additional samples for lactate (LA) and glucose (GLC) analysis were obtained 5 min into Phase C (C5) and at the end of Phase X (X10). Samples were analysed for packed cell volume (PCV), haemoglobin (HB), total plasma protein (TP), sodium (Na), potassium (K), chloride (Cl), anion gap (AG), plasma glucose (GLC) and lactate (LA), pH, PCO2, bicarbonate (HCO3) and base excess (BE). Shortening steeplechase distance by 50% under hot and humid conditions (2 min B) resulted in a consistent return to control measurements (4 min B) only for plasma LA. Changes in PCV, HB, TP, K and Cl were related more to the longer galloping distance in the 4 min B trials than to hot vs. cold laboratory conditions. Alternatively, changes in LA, GLC, pH, PCO2 and AG were more related to hot and humid laboratory conditions than they were to galloping distance. These latter variables, when combined with physical measures such as core temperature, bodyweight loss, point of fatigue on Phase C and recovery heart rates may serve as the best monitors of positive responses in future studies of proposed modifications to Phase C, rather than those variables which were more distance than weather-related.

Physiological effects of shortening steeplechase in a 3-day-event.

Various methods for modifying the Speed and Endurance portion (Day 2) of the 3-day-event have been proposed to aid horses in dealing with the hot and humid conditions expected during the next Olympic 3-day-events in Atlanta, Georgia USA in 1996. This study was designed to characterise the effects of shortening the distance required during the steeplechase (Phase B) in the face of Atlanta-like hot and humid weather conditions. Eight conditioned Thoroughbred horses (mean +/- s.e.m. age 3.75 years, range 3-5 years) underwent 3 randomised permutations of a standardised exercise test on a high speed treadmill. Each test consisted of trotting at 3.7 m/s for 10 min (Phase A); galloping at 11 m/s (Phase B) for 4 (cool, control laboratory conditions), 3 (hot and humid), or 2 (hot and humid) min; trotting at 3.7 m/s for 30 min (Phase C); and walking at 1.8 m/s for 10 min (Phase X). Subjects had Swan-Ganz catheters inserted into the pulmonary artery (PA) for measuring core temperature (PAT) in mixed venous blood every 2 min. Heart rate (HR) was measured by an on-board HR computer every 2 min. Rectal temperature (RT) was measured at the beginning (RTzero) and end (RT10) of Phase X using a mercury rectal thermometer as under typical field conditions. Pre- and post exercise bodyweights (bwt) were determined on a digital electronic scale. The point on Phase C at which each horse visibly fatigued and drifted toward the back of the treadmill was defined as the point of fatigue. Differences between treatments were tested for significance (P < 0.05) by repeated measures, Student-Neuman-Keul's and Student's tests where appropriate. Heart rate increased (mean 115.7-136.1) with the onset of trotting exercise in Phase A (P < 0.05), increased further with Phase B galloping (mean +/- s.e.m. 187.8-193.7, P < 0.05) and decreased with a return to trotting during Phase C (mean 108-130.5, P < 0.05) for all 3 treatments. Through the end of Phase C, there were no differences in HR between treatments (P > 0.05). From 3-10 min in Phase X (recovery), HR after 2 min B (mean 81.3-91) were lower than after 3 min B (mean +/- s.e.m. 98.4-100.5, P < 0.05) and were no different than 4 min B HR (mean 85.9-94.8, P > 0.05). Pulmonary artery blood temperature increased (mean 38.1-38.7) with trotting in Phase A (P < 0.05), increased further with Phase B galloping (mean 39.4-40.2, P < 0.05) for all 3 treatments and then decreased (mean +/- s.e.m. 39.3-39.9, P < 0.05) during Phase C under cool conditions (4 min B) but plateaued or continued to rise slightly under hot and humid conditions (mean 39.7-40.2). Throughout Phases C and X, PAT was lower for 4 min B than for either hot and humid treatment (P < 0.05). Bodyweight decreased after exercise for all treatments (P < 0.05) with the largest bwt loss (mean 10.9 kg) after 3 min B (P < 0.05) followed by 2 min B (8.3 kg) and then by 4 min cool B (6.5 kg). Point of fatigue was different between the 3 treatments (P < 0.05), with 4 min B the longest (mean +/- s.e. 24.8 min), followed by 2 min B (21.8 min), and then 3 min B (16.3 min). Rectal temperature was not different between the 3 treatments (P > 0.05), but there was a trend for both RTzero and RT10 to be highest after the 3 min B, lower after the 2 min B, and lowest after the 4 min cool B. It was concluded that there was a progressive gain in restoring cool weather performance and recovery by a progressive shortening of Phase B under hot and humid conditions, based on net weight loss, point of fatigue and recovery HR. Shortening Phase B by as much as 50% under hot and humid conditions still did not allow a complete return to cool weather performance and recovery. Further modifications to Phase C will be required in order to aid horses in net heat loss during Phases B and C.