EFFECTS OF LIGHTING REGIMEN AND GROWER DIET ENERGY CONCENTRATION ON ENERGY-EXPENDITURE, FAT DEPOSITION AND BODY-WEIGHT GAIN OF LAYING HENS

1. Mean metabolisable energy (ME) intakes and heat productions over a laying year were calculated for laying hens which had been submitted t o one of various lighting regimens and given either a normal or a high energy ration during the rearing period. 2. Daily ME intake and heat production per hen in the laying period were unaffected by either ligh ting regimen or grower diet. ME intake per kg W0.75 and heat productio n per kg W0.75 during lay increased significantly with laying photoper iod, was non-significantly higher following an 8-h rather than an 11-h rearing photoperiod, but was unaffected by dietary energy concentrati on. The increase in heat production (/kgW0.75) associated with a 1-h i ncrement in photoperiod was similar to predictions made from calorimet ric measurements of diurnal variation. 3. Efficiency of conversion of food to egg was unaffected by either lighting regimen or dietary energ y concentration. 4. Fat weight gain in lay was not influenced by light ing regimen, but was significantly lower in birds reared on the high, compared to the normal, energy grower ration. Fat-free weight gain in lay was unaffected by grower diet, but was significantly increased by photoperiods longer than 8 h. 5. ME intake and heat production per kgW 0.75 were negatively correlated' with age at first egg, but ME intake and heat production per bird d were not related to age at sexual matur ity.