Heart rate, blood pressure, cardiac output, and total peripheral resistance of single comb White Leghorn hens during an acute exposure to 35 C ambient temperature.

Two experiments were undertaken to determine selected cardiovascular responses of laying hens to a thermal challenge at 35 C ambient temperature. In the first, six Single Comb White Leghorn (SCWL) hens were exposed to 35 C and changes in systolic and diastolic blood pressure, heart rate, respiratory rate, and rectal temperatures were determined. In the second, seven SCWL hens were exposed to 35 C and changes in cardiac output, total peripheral resistance, blood pressure, heart rate, respiratory rate, and rectal temperature were monitored. In the first experiment heart rate and blood pressure decreased. In the second experiment there was a 58% increase in cardiac output and a 50% decrease in total peripheral resistance accompanied by a 9% decrease in mean blood pressure. Changes in cardiovascular tone preceded respiratory adjustments during acute heat challenges. This may represent one of the most efficient means of heat dissipation for the bird.