Treadmill exercise of calves with different iron supply, husbandry, and work load.

Experiments were designed to study physiological responses of male veal calves to treadmill exercise, dependent on iron intake (20, 35, and 50 mg of iron/kg of milk powder, respectively). Calves were fattened from 75 to 180 kg BW and were either restrained or could freely move on straw litter. The ADG and feed utilization as well as haemoglobin and the plasma iron concentration were positively influenced by iron intake (P < or = 0.05). At the end of the fattening period, calves walked on a treadmill at 0.8, 1.1, or 1.3 m/s for 15 min. Resting values of all cardiorespiratory parameters were similar in all groups. During exercise, heart rate, respiratory rate, respiratory minute volume, and oxygen consumption increased and after 3 min reached steady-state values, which depended on work load. The except was respiratory rate (which reached a maximum already at the lowest speed) and oxygen extraction rate (which remained at basal level during exercise, but in part decreased after walking). In calves fed the least amount of iron, hence with the lowest haemoglobin concentrations, oxygen consumption was lower than in other groups. In addition, cortisol concentrations increased most markedly during exercise in calves fed the least amount of iron.