Nutritional influences on carcass composition in the broiler chicken

During the period 1974-1984 the annual consumption of poultry meat has doubled to approximately 15 kg per person (Simpson, 1985).The determinant factor for this increased consumption is the low price of chicken compared with other meat.This has been a direct result of genetic selection for efficiency of production in terms of increased growth rate and improved feed conversion efficiency combined with a further understanding of a bird's environmental and nutritional needs.Twenty years ago it took 68 d for a broiler chicken toleach a slaughter weight of 2 kg whereas in 1985 it takes approximately 45 d (K.Laughlin, personal communication).As a broiler chicken grows its carcass composition changes.The most obvious change is the increase in carcass fat.Since a broiler chicken does not reach maturity, in terms of lean body mass, until about 30 weeks of age, broilers are slaughtered while relatively immature and, to date, the producer has given little or no attention to the composition of the end-product.However, the consumer is becoming far more health conscious and a recent report on diet and cardiovascular disease by the Committee on Medical Aspects of Food Policy (1984) recommended that 'The consumption of saturated fatty acids and fat in the United Kingdom should be decreased'.Since meat and meat products account for about 2570 of the saturated fat ingested, the report went on to state that 'Consumption of saturated fatty acids could be decreased now by substituting, for example, some non-fatty fish or poultry, e.g.chicken'.When compared with other meat, chicken has a slightly higher protein content but the total fat content is no more than 20% of that of other meat.The saturated fatty acid content is 5070 that of other meat and the level of polyunsaturated fats slightly higher, thus placing chicken very favourably with respect to human nutrition (Paul & Southgate, 1978).Although the carcass composition of the broiler chicken is to a certain extent genetically predetermined, it can be influenced by nutritional factors, of which the most widely investigated is the dietary energy:protein (E:P) value. The dietary E:P valueFrapps (1943) demonstrated that chickens with widely differing amounts of body fat could be produced by manipulation of the dietary E:P value.