Some Physiological Effects of High Environmental Temperatures on the Laying Hen

Abstract HOMEOTHERMY BIRDS are homeotherms and so are less vulnerable to environmental temperature changes than poikilotherms in respect of both functional efficiency and danger of tissue damage. The price that has to be paid for the benefits conferred by homeothermy is that body temperature cannot be allowed to fluctuate beyond relatively narrow limits without deterioration in normal functional efficiency. Within a limited, if ill defined, environmental temperature range, the laying hen is able to balance thermogenesis and thermolysis so that its body temperature remains at the optimum for normal body functions. Complete uniformity of body temperature is possible only if no heat exchange occurs between the body and its environment. Birds, however, constantly produce heat and lose it to the environment so that there is a thermal gradient from the warm interior (core) to the cooler surface (shell). Sensible heat constantly flows from the deep body centre to the outside in…