Effect of changes in dietary energy intake and environmental temperature on heat tolerance in the fowl.
The improvement in heat tolerance acquired during the acclimatization of laying hens to intermittent heat stress was lost or considerably reduced when energy intake increased following the addition of maize oil to the diet. The oxygen consumption (VO2) of acclimatised hens increased after the addition of maize oil to the diet. Reducing the environmental temperature (Ta) from 30 degrees to 10 degrees C prevented the development of acclimatization if the heat stress commenced soon after the change of Ta; if the heat stress commenced 5 weeks after the change of Ta acclimatization took place normally. Reducing the Ta from 30 degrees to 10 degrees C resulted in an increased VO2 and food intake. The administration of triiodothyronine increased VO2 and reduced the heat tolerance of acclimatised hens. It is concluded that heat tolerance, despite being reinforced by regular exposure to heat stress, remains susceptible to changes in energy metabolism brought about by dietary or environmental means.
D000064:Acclimatization; D000818:Animals; D002645:Chickens / Q000502:physiology*; D002149:Energy Intake; D004734:Energy Metabolism; D006358:Hot Temperature; D010101:Oxygen Consumption; D011201:Poultry Diseases / Q000503:physiopathology; D013312:Stress, Physiological / Q000503:physiopathology / Q000662:veterinary; D013696:Temperature