A comparison of the energy and nitrogen metabolism of broilers selected for increased growth rate, food consumption and conversion of food to gain

Abstract

1. Calorimetric measurements were made on 5‐week‐old male chickens sampled from the third generation of three lines selected for either increased live‐weight gain (W), food consumption (F), or food conversion efficiency (E). A control line (C) was also measured. 2. Food intake and food conversion ratio were greater (P<0.05) in the F line than in the E and C lines. 3. Metabolisability of the diet was 0.8% higher in the E line than in the other lines. 4. Metabolisable energy (ME) intake and heat production were greater (P<0.05) in the F line than in the E and C lines, and energy balance was greater (P<0.05) in the F than in the W and E lines. 5. During starvation, excreta energy and heat production were greater (P < 0.05) in the F than the other lines. 6. Availability of ME (net energy) was the same (85%) for all lines but calculated daily maintenance energy requirements (kJ ME/kgW) were W, 860; F, 937; E, 796 and C, 810. 7. By 9 weeks the F line contained more fat and less water than lines E and C.