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Title: The hormonal basis of decreased growth rate in broiler chickens exposed to high environmental temperatures
Author: Kan, P.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1994
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Broiler chickens and other meat animals grow very slowly at high ambient temperatures (such as those experienced in tropical and subtropical countries), and also exhibit a high mortality rate under these conditions. Experimental evidence suggests an interaction between thyroid hormones and growth hormone (GH) in the control of growth rate in heat stressed chickens. It is known that changes in the circulating concentrations of thyroid hormones are associated with altered growth rate in several species. Whilst thyroxine (T4) is chiefly secreted by the thyroid gland, in chickens the majority of the circulating tri-iodothyronine (T3) is produced in other tissues by 5'-monodeiodination, primarily in the liver. Regulation of hepatocyte deiodinase function is thus central in the control of thyroid hormone metabolism. The effects of the climatic environment upon the secretion and metabolism of thyroid and growth hormones (the thyrotrophic and somatotrophic axes) and their interactions may thus play a role in the alterations in growth rate associated with heat stress. The present project was designed to investigate the responses of plasma thyroid and growth hormone to different degrees of heat stress (21, 25, 29, 32 and 35oC) and to elucidate the mechanisms involved in the regulation of thyroid hormone economy under a range of environmental conditions. These studies have confirmed that chronic heat stress depresses the circulating plasma concentrations of T4 and T3 in broiler chickens concomitant with reduced growth rate. The decreased plasma concentrations of T4 and T3 resulting from exposure to high ambient temperatures per se are not a consequence only of reduced food intake. The sensitivity of the peripheral 5'-monodeiodination of T4 to T3, to administration of exogenous thyrotrophin-releasing hormone (TRH) or chicken growth hormone (cGH) was decreased in chronically heat stressed broilers.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available