Effects of heat production attributable to forced walking on thermoregulatory physiological responses of chickens in a warm environment

1. To determine the effects of heat production on thermoregulatory physiological responses, 5 chickens were forced to walk to increase heat production. The study consisted of two experiments. One involved 3 walking speeds (8, 16 and 24 m/min) at 25 degrees C ambient temperature. The other involved a single walking speed of 16 m/min at 3 ambient temperatures (20, 25 and 30 degrees C). Heat production, heart rate, abdominal temperature, shank skin temperature and respiration rate were measured before, during and after walking. 2. Heat production, heart rate and respiration rate increased abruptly after the start of walking and with increase in walking speed. At the start of walking, an abrupt increase in abdominal temperature occurred independently of walking speed and environmental temperature; then, as walking continued, abdominal temperature increased further with increasing walking speed and increasing environmental temperature. Shank skin temperature declined at the initiation of walking, then increased. 3. Heat production and heart rate recovered rapidly after walking, while shank skin temperature and respiration rate increased and then recovered, except at 30 degrees C. 4. A proportion, 17% to 35%, of the increased heat production was stored, increasing body temperature during walking. After walking, the stored heat was lost by means of panting until abdominal temperature recovered to 41 degrees C or shank skin temperature recovered to 37 degrees C. 5. These results suggest that the greatly-increased heat production attributable to forced walking leads to abrupt thermoregulatory physiological responses, and the heat stored in the body is actively dissipated by panting until abdominal temperature recovers to the pre-walking level. The chief mode of heat loss of birds changes with deep body temperature.