Respiration in Exercising Fowl. III. Ventilation

Minute volume ⁠, respiratory frequency (f) and tidal volume (V_T) were continuously measured in domestic fowl running on a treadmill at speeds of 1·24–4·3 km h⁻¹ in air temperatures of 18 ± 2 °C and 35 ± 2 °C. Oxygen extraction (E) was estimated using previously measured values of oxygen consumption.

At 18±2 °C and V_T rose abruptly at the start of exercise and and f continued to rise except at the slower running speeds. and f continued to rise throughout exercise at all speeds in the heat-stressed birds. In both groups V_T reached a maximum at the start of exercise then fell to a new steady-state level. Steady-state ⁠,f and V_T increased with exercise speed at 18 ±2 °C. At 35-37 °C steady-state and V_T increased with speed but f changed relatively little.

E remained close to resting (0·21) at low speeds in room temperatures but decreased to 0·17 at 4·3 km h⁻¹. In contrast E rose from 0·05 at rest in heat-stressed birds to 0·14 at 3·6 km h⁻¹. The changes in oxygen extraction and respiratory pattern in the two groups during exercise are discussed in connexion with the control of ventilation by thermal and non-thermal factors. It is suggested that the latter play a predominant role during heavy exercise and that this accounts for the convergence of respiratory patterns in both heat-stressed and non heat-stressed birds at maximum work rates.