ENERGY AND PROTEIN-METABOLISM BETWEEN 3 AND 6 WEEKS OF AGE OF MALE BROILER-CHICKENS SELECTED FOR GROWTH-RATE OR FOR IMPROVED FOOD EFFICIENCY

1. A new open-circuit respiration unit consisting of 6 respiration cha mbers, gas analysis unit and data-acquisition system is briefly descri bed. 2. Energy and protein metabolism in broiler lines selected for im proved food efficiency (FC) or for growth rate (GL) were measured week ly from 3 to 6 weeks of age. 3. Gross and apparent metabolisable energ y intake per kg W-0.75 was On average higher for GL than for FC chicke ns without differences in metabolisability. Fed and fasted heat produc tion per kg W-0.75 did not differ between the lines. FC chickens retai ned less energy per kg W-0.75 than GL chickens. 4. FC chickens deposit ed much less of the retained energy as fat than their GL counterparts and also showed greater protein conversion efficiency. The leaner comp osition of the body weight gain in FC chickens was confirmed by the es timated lower fat deposition per kg W-0.75 and by the lower fat:protei n ratio.