INTERMITTENT LIGHTING AND BROILER PRODUCTION .2. EFFECT ON ENERGY ANDON NITROGEN-METABOLISM

In the present experiment, the effect of the intermittent lighting sch edule 1 h light (L):3 h darkness (D) on energy and nitrogen metabolism of female broilers at different ages was compared with continuous ill umination (24L:0D) by using open circuit respiration chambers. Changin g from continuous to intermittent lighting at 9 days of age induced a transient depression in growth rate that was followed by compensatory- growth. At a younger age, when growth was retarded, chickens reared un der 1L:3D produced less heat per kilogram metabolic body weight, retai ned more energy as protein, retained dietary protein with a higher eff iciency and deposited less fat, resulting in a higher protein: fat rat io of the achieved body weight gain. At 35 days of age, when compensat ory growth was manifested, chickens reared under 1L:3D produced more h eat which can be explained by the leaner body weight gain. The efficie ncy of dietary protein retention was also higher for chickens kept in intermittent than in continuous lighting. At 44 days of age however, t he protein:fat ratio was lower for the heavier 1L:3D chickens. It is s uggested that when the growth trajectory is altered by imposing interm ittent lighting at a young age, the onset of the fat growth wave is po stponed initially but does not persist when chickens attain a heavier body weight.