Selecting Broilers for Low or High Abdominal Fat: Comparison of Energy Metabolism of the Lean and Fat Lines

Two experiments were conducted to compare energy requirement for maintenance and energy efficiencies of lipid and protein synthesis in males of either a lean line (LL) or a fat line (FL). Metabolizable energy content of the diet as measured by the two lines did not differ. When fed the same limited amount of feed, the birds of the LL always exhibited faster growing rates and a lower level of fat synthesis. The feed to gain ratio was always lower in LL. No between-line differences were found either for maintenance energy requirements or efficiency of energy required for lipid and nonlipid tissue synthesis. It is concluded that hyperphagy is not the primary cause of obesity in FL. The genotypes differ in the use made of the lipid or the protein metabolic pathways. This mechanism is under physiological control, these lines exhibiting a different plasma glucose insulin balance.