BLOOD SYSTEM RESPONSE OF CHICKENS AO CHANGES IN ENVIRONMENTAL-TEMPERATURE

Hemodynamic changes were studied in broiler chickens during exposure t o constant temperatures (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 temperatures (30 and 35 C) plasma volume (PV) was s ignificantly high. A linear relationship between hematocrit and heart weight was observed and indicates an adaptation of heart mass to chang es in cardiac output and hematocrit to meet the demands of increased b asal metabolic rate. Only during the diurnal temperature cycle of 15:3 5 C did a significant increase in PV occur when ambient temperature (T -a) was raised from 15 to 35 C. Acute exposure of chickens to high tem perature 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 s upply of oxygen to accommodate changes in heat production. The signifi cant hypervolemia observed at high temperatures could occur to provide the fluid needed for heat dissipation by panting. The lack of respons e of the blood system to acute temperature changes may be at least par tially responsible for the chickens' failure to control body temperatu re.