Responses of two genotypes of chicken to the diets and stocking densities typical of UK and 'Label Rouge' production systems: I. Performance, behaviour and carcass composition.
'Label Rouge' (LR) chickens are reputed to possess improved sensory characteristics compared with birds reared under intensive conditions. The effects on body weight, food utilisation, behaviour and carcass composition, of genotype (Ross I vs ISA '657'), diet (conventional UK broiler vs LR) and stocking density (17.0 birds m(-2),vs 4.25 birds m(-2)) were evaluated in a 2 × 2 × 2 experiment. ISA birds were grown to 83 days, and compared with Ross birds grown to 48 days; additionally ad libitum and control-fed Ross birds were grown to 83 days. Performance and behaviour parameters were assessed empirically. The effects on carcass composition were evaluated using standardised carcass dissection techniques and analysed by analysis of variance. ISA birds grown under LR conditions to 83 days had similar body weights to Ross birds grown under UK broiler conditions to 48 days, but LR birds consumed more food, and converted food into meat less efficiently. LR birds had no mortality, whilst UK broiler mortality was 11.3%. Under similar conditions, Ross birds had a faster body weight gain, a larger food intake, but more efficient food conversion ratio and higher incidence of mortality. Birds stocked 17.0 m(-2) had lower body weights, consumed less food and, when fed UK diets, converted food less efficiently than birds stocked 4.25 m(-2). Both genotypes had a faster growth rate on UK diets, similar food intakes, and, as a result, better food conversion than birds given LR diets. LR and UK broiler birds had similar carcass component weights, breast meat yields, and total meat yield, but LR birds had less meat on the frame, larger drumsticks and more meat on the wings. Under similar conditions, ISA birds had a larger percentage of wing and total bone, but a smaller percentage of breast meat and total meat yields. When Ross birds had controlled growth, total meat, bone and skin yields were similar to those of ISA birds. Birds stocked 4.25 m(-2) had more breast meat and larger frames than, but similar meat, bone and skin yields to, birds stocked 17.0 m(-2). Most carcass components were heavier in birds fed UK broiler diets, but, on a percentage basis, these birds had larger thighs, but smaller drumsticks.