Effects of conditioning and maximal incremental exercise on oxygen consumption in sheep

To assess the suitability of sheep for exercise studies, the effect of incremental exercise and conditioning on oxygen consumption (VO2) was studied. Six sheep were adapted to a treadmill and subsequently trained 8 weeks. The sheep were then studied, in random order, using 3 incremental exercise protocols (EX-1, EX-2, and EX-3). The protocols were chosen to approximate high (EX-1), moderate (EX-2), and low (EX-3) intensity exercise by varying treadmill speed and incline. The sheep were then conditioned for an additional 12 weeks and retested on the EX-2 protocol. During exercise, VO2, gas exchange ratio (R), and rectal temperatures (Tb) were recorded. All 3 protocols resulted in significant increases in VO2, R, and Tb (P less than 0.05). Maximum VO2 for EX-1, 49.9 +/- 5.0 ml/min/kg of body weight, was significantly greater than maximum VO2 for EX-2 and EX-3, 37.8 +/- 6.5 and 42.3 +/- 6.0 ml/min/kg, respectively (P less than 0.05), whereas maximum R and maximum Tb were similar. After the additional 12-week conditioning, time on the treadmill increased 40% from 9.58 +/- 0.87 to 13.4 +/- 0.44 minutes, and maximum VO2 increased 27% to 48.1 +/- 9.1 ml/min/kg. These data indicated that maximum VO2 varied with intensity of the exercise, 12 weeks of maximal exercise conditioning was sufficient to produce a measurable training effect (ie, increase endurance and maximum oxygen consumption) and sheep are suitable for maximal exercise studies where VO2 measurements are desired.