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

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 less than 0-05) in the F line than in the E anc 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 less than 0-05) in the F line than in the E and C lines, and energy balance was greater (P less than 0-05) in the F than in the W and E lines. 5. During starvation, excreta energy and heat production were greater (P less than 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.