Alp and valley cattle: exercise in cold, hot and high environments.

Two groups of cattle, one kept on an alpine pasture (1700--2600 m altitude) for 5 summer months and the kept in a barn at 400 m, were subjected to treadmill exercise for 15 min at a speed of 2 km/h in environments of 15 degrees C, -10 degrees C, 35 degrees C (all at 400 m) and at simulated altitude of 3500 m (at 15 degrees C). In the resting conditions, the alpine cattle had higher respiration rates and body temperatures at an air temperature of 35 degrees C than the valley cattle which was attributed to a greater hair insulation and possibly a low responsiveness of the sweat glands. At 3500 m, the alpine animals had higher resting heart rates than the valley animals, which was attributed to a greater blood volume. After exercise, heart rates in the alpine cattle were from 10--19 beats/min lower than in the valley cattle, due to exercise conditioning in the former animals. This training effect on heart rates in the alpine animals was paralleled by reduction in intrinsic heart rates (using atropine and propranolol as blocking agents). Atropine blockade also indicated that exercise-trained cattle have a lower vagus tone compared to non-exercise-trained cattle.