Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2001
Publication Date: 12/1/2001
Citation: 2001 Poultry Science 80:1662-1666 Interpretive Summary: Broiler chickens lose their ability to thermoregulate efficiently under extreme conditions because of their rapid growth rate. High environmental temperatures will reduce production efficiency of chickens, and under extreme conditions, result in high mortality rates. This research was conducted to take advantage of the immature nature of neonatal chick by inducing thermotolerance at an early age. Thermal conditioning is a uniqu phenomenon is that it elicits two mutually contradictory effects, increased growth rate and increased thermotolerance. The objective of this study was to assess the optimal timing and temperature for the thermal conditioning process in the neonatal chick. It was found that an ambient temperature exposure between 36 and 37.5 C, applied at 3 days of age provides the optimal thermal conditioning for broiler chickens. It was also observed that thyroid hormone levels were significantly lower in thermally conditioned chicks, indicating that the thermal conditioning response is mediated in part by components of the endocrine system. The results of this study will provide poultry producers with a management tool by which broiler chickens may be able to tolerate high environmental temperatures. The results of this study will be of interest to both producers and other scientists.
Technical Abstract: Thermal conditioning of chicks results in improvements in performance and thermotolerance at marketing age. Conditioning has been found to be a sensitive process, dependent on age and the temperature used. The objective of this study was to assess the optimal timing and temperature for the conditioning processes. Two experiments were conducted on male broiler chickens: the first aimed to find the optimal age for thermal conditioning (1 to 5 d of age); the second evaluated the optimal thermal conditioning temperature between 36 and 40.5 C. At 42 d of age chickens were thermal challenged to evaluate their ability to cope with acute heat stress. The highest body weight was achieved when thermal conditioning had been applied at the age of 3 d, and it coincided with low feed intake and significantly higher feed efficiency. These treated chickens showed significantly lower mortality under thermal challenge, and significantly lower T3 concentration nin Trial 2. Chicks that had been thermally conditioned at Ta of 36 and 37. C at the age of 3 d demonstrated the best performance characteristics and the ability to reduce T3 concentration to the lowest levels during thermal challenge. It can be concluded that a Ta between 36.0 and 37.5 C, applied at 3 d of age provides the optimal thermal conditioning for chickens.