Effects of exogenous thyroid releasing hormone and thyroid hormones on growth and plasma thyroid and growth hormone concentrations of broilers kept at high temperatures
1989
Sinurat, A.P. (Balai Penelitian Ternak, Bogor (Indonesia)) | Balnave, D. | McDowell, G.H.
Chickens kept in a high temperature environment (21 deg. - 35 deg. C) and fed either ad libitum or restricted amounts of food were given daily intravenous injections of thyroid releasing hormone (TRH), thyroxine (T4) or triiodothyronine (T3) from 32-38 days of age. Plasma concentrations of T3, T4 and growth hormone (GH), food intake, growth rate and the weights of abdominal fat, thyroid glands and crops of birds were measured. Injections of TRH increased plasma concentrations of T3 (throughout the period of injections) as well as T4 and GH (on the first day of injections). These responses were most common in birds given free rather than controlled access to food. Responses to injections of T3 and T4 were not detected except on the first day on injections when plasma GH was decreased in T3 injected birds, and plasma T4 increased in T4 injected bird. Inspite of increases in plasma hormones after injection with TRH there were no changes in food intake, growth rate or amount of abdominal fat. Weights of thyroid glands in birds treated with TRH increased in birds fed ad libitum and decreased in feed-restricted birds. Crop size increased in birds on restricted intakes.
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