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Energy Metabolism in Genetically Fat and Lean Chickens: Diet- and Cold-Induced Thermogenesis¹

Agricultural and Food Research Council Institute for Grassland and Animal Production, Poultry Department, Roslin, Midlothian EH25 9PS, Scotland

Energy metabolism was investigated by using indirect calorimetry in growing chickens of similar body weight but genetically selected for high (fat line, FL) or low (lean line, LL) abdominal fat content. Twelve 5- and 7-wk-old male chickens of each line were exposed at two different ambient temperatures, 10 and 25°C. Two birds from the same line were placed in each calorimeter chamber for a 6-d period (2 d fasting and 4 d feeding). Similar food intakes and metabolizabilities of diet corrected for nitrogen balance revealed that FL and LL chickens ingested the same amount of metabolizable energy (ME). Moreover diet-induced thermogenesis did not appear to be defective in FL birds, and the maintenance ME requirement was similar in both lines. However, the partition of retained energy between fat and protein did differ, with increased protein deposition and conversely, decreased fat retention in LL chickens, irrespective of age or ambient temperature. FL birds catabolized a greater proportion of dietary amino acids as confirmed by the increase in uric acid excretion. Finally, energy expenditure was significantly and similarly enhanced in both genotypes by cold exposure.

KEY WORDS: • obesity • energy • thermogenesis • chicken • genetic

¹ Part of the subject matter of this paper has been presented as a short communication at a meeting of the Nutrition Society, Newcastle-upon-Tyne, 16–17 September, 1986 [Proc. Nutr. Soc. 46:34A, 1987].

² Present address: Station de Recherches Avicols. Institut National de la Recherche Agronomique 37380 Monnaie, France.

Manuscript received 17 February 1988. Revision accepted 23 May 1988.