Cardiovascular responses of the chicken to seasonal and induced temperature changes.

Blood pressure and cardiac output decline as ambient temperature rises in birds acclimatized to both seasonal- and induced-temperature changes, in contrast to the response usually observed in unacclimatized mammals. The decline in chickens is due to a lowered vascular resistance and blood volume. These circulatory adjustments may be related to the fact that excess heat in birds is dissipated through the respiratory system rather than through the skin.