Maximal ventilation assessment in healthy calves.

Abstract In order to define a reliable method for estimating maximal ventilation in cattle, 12 healthy calves underwent a rebreathing trial and injections of increasing doses of lobeline, a respiratory analeptic. The effects of these tests on the main ventilatory parameters (tidal volume, V T ; respiratory frequency, f R and minute volume, ·V E ) recorded during the 15 s of maximal response were studied and compared. The sharp rise in ·V E (4.8 times higher than the resting value) observed during the rebreathing trial was mainly due to an increase in V T . This rise in ventilation was the highest ever reported in calves. Lobeline dose-dependently enhanced ventilation up to a threshold dose of 0.25 mg/kg, which always produced a maximal response. This maximal response (3.7 times higher than the resting value), reflecting both an increase in f R and V T , was reproducible at an interval of 12 h and was highly correlated with that observed during the rebreathing trial ( R = 0.98, P