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Performance and physiological variables in broiler chicken lines differing in susceptibility to the ascites syndrome. 2. Effect of ambient temperature on partial efficiencies of protein and fat retention and plasma hormone concentrations

Buys, N., Scheele, C.W., Kwakernaak, C., Decuypere, E.
British poultry science 1999 v.40 no.1 pp. 140-144
broiler chickens, line differences, ascites, ambient temperature, selection criteria, liveweight gain, feed intake, heat production, oxygen consumption, energy balance, blood plasma, thyroxine, triiodothyronine, somatotropin, thyroid function, selection response, biological resistance
1. Male broilers of 5 genetic stocks (A, B, C, D and E), selected in different ways for fast growth and low food conversion rate (FCR) and differing in sensitivity to ascites, were subjected to 2 different ambient temperature (Ta) step-down programmes: normal (HT) and low (LT) TA. 2. Ascites incidence was followed daily. Growth and food intake were measured weekly. Heat production (Hp), oxygen consumption (Oxc} and energy metabolism parameters were calculated according to the comparative slaughter method. At week 4 blood samples were taken for the analysis of plasma T(4), T(3), growth hormone (GH) and insulin-like growth factor-I (IGF-1) concentrations. 3. Within-line changes of GH and IGF-1 point to the relative independence of both hormone concentrations. 4. Partial protein efficiency was higher in lines with lower GH, especially at LT. 5. The increase in plasma T(3) concentration at LT was accompanied by a decrease in relative fat deposition from the increased energy expenditure. 6. The combination of fast growth and low FCR, linked to a low plasma T(4) concentration at LT is indicative of a thyroid insufficiency which is related to an increased occurrence of ascites in these lines.