RESPONSES OF 2 GENOTYPES OF CHICKEN TO THE DIETS AND STOCKING DENSITIES TYPICAL OF UK AND LABEL ROUGE PRODUCTION SYSTEMS .1. PERFORMANCE, BEHAVIOR AND CARCASS COMPOSITION

'Label Rouge' (LR) chickens are reputed to possess improved sensory ch aracteristics compared with birds reared under intensive conditions. T he effects on body weight, food utilisation, behaviour and carcass com position, of genotype (Ross I vs ISA '657'), diet (conventional UK bro iler vs LR) and stocking density (17.0 birds m(-2) vs 4.25 birds m(-2) ) were evaluated in a 2 x 2 x 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 car cass 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 fo od, and converted food into meat less efficiently. LR birds had no mor tality, whilst UK broiler mortality was 11.3%. Under similar condition s, Ross birds had a faster body weight gain, a larger food intake, but more efficient food conversion ratio and higher incidence of mortalit y. Birds stocked 17.0 m(-2) had lower body weights, consumed less food and, when fed UK diets, converted food less efficiently than birds st ocked 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 b irds given LR diets. LR and UK broiler birds had similar carcass compo nent weights, breast meat yields, and total meat yield, but LR birds h ad less meat on the frame, larger drumsticks and more meat on the wing s. Under similar conditions, ISA birds had a larger percentage of wing and total bone, but a smaller percentage of breast meat and total mea t 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 basi s, these birds had larger thighs, but smaller drumsticks. (C) 1997 Els evier Science Ltd.