Abstract
Effects of increased summer temperatures on poultry production are becoming more pronounced due to global warming, so it is important to consider approaches that might reduce heat stress in chickens. Thermal conditioning in chickens in the neonatal period can improve thermotolerance and reduce body temperature increases when birds are exposed to high ambient temperature later in life. The objective of this study was to investigate physiological and molecular changes associated with heat production and hence body temperature regulation under high ambient temperatures in thermally conditioned chicks. Three-day-old broiler chicks (Chunky) were thermally conditioned by exposure to a high ambient temperature (40°C) for 12 h while control chicks were kept at 30°C. Four days after the treatment, both groups were exposed to 40°C for 15 or 90 min. The increase in rectal temperature during 90 min of exposure to a high ambient temperature was less in thermally conditioned than control chicks. At 15-min of re-exposure treatment, gene expression for uncoupling protein and carnitine palmitoyletransferase 1, key molecules in thermogenesis and fatty acid oxidation, were significantly higher in pectoral muscle of control chicks but not conditioned chicks. Hepatic argininosuccinate synthase (ASS) decreased and hepatic argininosuccinate lyase (ASL) increased after reexposure to a high temperature. The concentrations of hepatic arginosuccinic acid, and ASS and ASL expression, were upregulated in conditioned chicks compared with the control chicks, indicating activity of the urea cycle could be enhanced to trap more energy to reduce heat production in conditioned chicks. These results suggest thermal conditioning can reduce the increase in heat production in muscles of chickens that occurs in high ambient temperatures to promote sensible heat loss. Conditioning may also promote energy trapping process in the liver by altering the heat production system, resulting in an alleviation of the excessive rise of body temperature.
Highlights
The increased magnitude and duration of elevated summer temperatures due to the advance of global warming is a pressing challenge that should be addressed from the viewpoint of adverse effects on health and from considerations of food production
Rectal temperature increased during the heat challenge (P < 0.001) in control chicks and in chicks that had experienced thermal conditioning
Our results agreed with prior studies that showed early thermal conditioning to enhance body weight gain in chickens [14]
Summary
The increased magnitude and duration of elevated summer temperatures due to the advance of global warming is a pressing challenge that should be addressed from the viewpoint of adverse effects on health and from considerations of food production. Livestock can show loss of appetite and reduced rates of weight gain when they experience heat stress in summer and in extreme cases animals can die due to heat stress [1,2,3]. If the incidence of heat stress in animals continues to increase at the current rate adverse effects due to summer heat will start to occur in areas that are currently cold, leading to decreases in livestock productivity in summer in these areas [4]. Whilst a variety of approaches such as improvements in rearing systems and the supply of feed additives that mitigate heat stress have been applied, effective strategies are needed to reduce the effects of elevated temperatures on chickens. Breeding takes a long time and new strategies are needed to reduce effects of heat stress on chickens
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