RESPONSES OF BODY-COMPOSITION, GROWTH AND FOOD EFFICIENCY TO DIETARY-PROTEIN IN GENETICALLY LEAN AND FAT BROILERS UP TO 7 WEEKS OF AGE

1. Growth, food intake and abdominal fatness were measured at 7 weeks of age in male and female broilers from genetically lean and fat lines fed on isoenergetic diets containing 160, 190, 210, 230 and 260 g crude protein/kg from hatching. 2. The mean proportions of abdominal fat decreased from 39 to 20 g/kg body weight in the fat line and from 26 to 11 g/kg in the lean line over this range of protein concentrations. 3. Protein requirements, for optimum growth as a proportion of the diet did not differ between the lines but the lean line was less tolerant of inadequate dietary protein. 4. In birds fed on the same diet, conversion efficiencies of food (FCE) and dietary protein (PCE) were always superior in the lean line but energetic efficiency (EE) was similar in good growing birds of both lines. 5. When dietary protein was adequate for growth and body compositions were equalised in the two lines (by feeding higher protein diets to the fat line), lean line birds had 10% better FCE, 6% better EE and 33% better PCE. 6. It is concluded that genetic selection is a more effective and economic means of producing leaner broilers than dietary manipulation. © 1990, Taylor & Francis Group, LLC. All rights reserved.