Respiratory and cardiovascular responses of the exercising chicken to spinal cord cooling at different ambient temperatures. II. Respiratory responses.

We measured oxygen consumption (VO2), carbon dioxide production (VCO2), minute volume (VE), respiratory frequency (f) and tidal volume (VT) of chickens during 15 min treadmill exercise at 0.5 ms-1 and 0.8 ms-1 at thermoneutral (23 degrees C), low (9 degrees C) and high (34 degrees C) ambient temperature (Ta); the vertebral canal was cooled to 34 degrees C during the middle 5 min of each exercise period. Temperatures of the vertebral canal (TVC) and rectum (Tre) were also measured. Exercise at 0.5 ms-1 caused increases in O2 consumption, CO2 production, minute volume and tidal volume compared to resting controls at each Ta. Minute volume and respiratory frequency were higher and tidal volume was lower in birds exercising at 34 degrees C than at 23 or 9 degrees C. Spinal cord cooling during exercise (0.5 ms-1) at 9 degrees C caused further increases in O2 consumption, tidal volume and respiratory frequency almost equivalent to those produced by an increase in the running speed to 0.8 ms-1. Spinal cord cooling during exercise (0.5 ms-1) at 23 degrees C did not significantly affect O2 consumption, CO2 production, minute volume, tidal volume or respiratory frequency. Spinal cord cooling during exercise (0.5 ms-1) at 34 degrees C did not affect O2 consumption or CO2 production, but caused decreases in minute volume and respiratory frequency and an increase in tidal volume. We conclude that the domestic fowl exhibits spinal thermosensitivity during exercise, although these responses appear to be smaller than those previously reported for the resting bird. Decreased external temperature potentiates the effects of spinal cord cooling during exercise.