Blood system response of chickens to changes in environmental temperature

Abstract

ABSTRACT Hemodynamic changes were studied in broiler chickens during exposure to constant tempera-tures (10 to 35 C) or diurnal temperature cycles (10:30 C and 15:35 C), and during acute heat or cold. Packed cell volume (PCV) was significantly high at low constant temperatures (10 and 15 C), whereas at high tempera-tures (30 and 35 C) plasma volume (PV) was signifi-cantly high. A linear relationship between hematocrit and heart weight was observed and indicates an adaptation of heart mass to changes in cardiac output and hematocrit to meet the demands of increased basal metabolic rate. Only during the diurnal temperature cycle of 15:35 C did a significant increase in PV occur when ambient temperature (Ta) was raised from 15 to 35 C. Acute exposure of chickens to high temperature did not affect PV or PCV, but resulted in hyperthermia (44.7 ± 0.4 C). Changes in PCV are probably related to modulation of the supply of oxygen to accommodate changes in heat production. The significant hypervole-mia observed at high temperatures could occur to provide the fluid needed for heat dissipation by panting. The lack of response of the blood system to acute temperature changes may be at least partially responsi-ble for the chickens ' failure to control body temperature. (Key words: chronic and acute exposure, ambient temperature, plasma volume, packed cell volume, broiler