Effects of acclimatization to heat and cold on heart rate in chickens

Cardiovascular responses to adrenergic agents in different acclimation states in the rock pigeon (Columba livia)

The effect of propranolol on heart rate (fH) was measured in season-acclimatized pigeons. Propranolol treatment decreased fH in winter-acclimatized pigeons, accelerated fH in summer-acclimatized pigeons, but had no effect on fH in spring-acclimatized pigeons. The effect of propranolol in summer-acclimatized pigeons is opposite to that observed in mammals. Interestingly, isoproterenol produced a propranolol-like cardioacceleration in heat-acclimated pigeons. We suggest that propranolol affects fH in summer-acclimatized pigeons via two opposing routes-a direct and a peripheral indirect route. We also suggest that the cardiovascular effects of propranolol are involved in the capacity of the pigeon to evaporate water from its skin.

The effect of heat on the intestinal and pancreatic levels of amylase and maltase of laying hens and broilers

The effects of exposing laying hens and broilers daily to intermittent periods of 4 hr heating at 42 degrees C on the intestinal and pancreatic levels of amylase and maltase were investigated. The initial exposure to heat, characterized by heat stress, brought about a significant increase in the duodenum and jejunum parts of the tetra breed hen and only in the duodenum of broilers. The levels of amylase in the distal parts of the intestine of both breeds sharply decreased. The increase in amylase levels in the proximal parts of the intestine under the conditions of initial heating vanished after 3 days of heating; its levels continued to fall in the distal parts. In heat acclimatized laying hens the levels of amylase were lower than those of the control hens both in the intestine and pancreas. The pancreatic level of amylase was reversely related to the levels in the intestine. It is assumed that the intestinal level of amylase is regulated by the pancreas. These findings indicate that the pancreas plays an important role during the adaptation of chickens to heat, through the regulation of intestinal level of amylase. The response in maltase level to heat stress and heat acclimatization was insignificant.

Caloric value of cardiac response to hot environments

Single Comb White Leghorn hens were placed in a controlled temperature chamber, initially at 26 C and subsequently raised to 35 C. Recordings of the surface and rectal temperatures, respiratory rate, heart rate, and oxygen consumption were made at the 26 C basal temperature and compared with those made at the 35 C ambient temperature. Sequential doses of saline and atropine were injected following the thermoregulatory response of birds to 35 C. The thermal challenge resulted in an average increase of 53 breaths per minute in the respiratory rate during the pre-injection period at 35 C and rose steadily to the end of the thermal challenge. The saline elicited no effects on any parameter measured; however, the atropine resulted in a mean increase of 62 beats per minute in the heart rate. There was no difference in the pre-atropine heart rate at 35 C and the basal heart rate at 26 C. Following the atropine induced increase in heart rate there was a 13% increase in energy expenditure. Thermal-bradycardia in hot environments may represent a first line of defense against hyperthermia by reducing the added heat load.