Energy efficiency of commercial free-range laying hens of different body weight and ranging activity

Within a free-range flock, some hens prefer to spend majority of their time in the shed, while others frequently access the range. Development of these sub-populations may be associated with different hen performance. Evaluation of energy efficiency of laying hens provides important knowledge for optimal egg production. The aim of this study was to determine net energy utilisation of these subpopulations obtained from a free-range system. Forty-eight Lohmann brown hens at 72weeks of age were selected from a commercial free-range farm and classified as heavy or light body weight (average 2.01kg and 1.68kg respectively, n=24) and as rangers (accessed the range on 84.1 % of the available days; n=24) or stayers (accessed tl1e range on 7.17% of available days; n=24). The energy efficiencies were evaluated in a close-circuit respiratory chamber system. Stayers had significantly higher metabolisable energy intake/bird/d/BW^0.75 (0.852±0.019 vs 0.798±0.016 MJ/g; P=0.025), heat production/BW^0.75 (0.637±0.069 vs 0.607±0.057 MJ; P=0.005), heat increment/BW^0.75 (0.267±0.007 vs 0.237±0.006 MJ;P=0.005) and retained nitrogen/ bird/d (1.59±0.02 vs l.46±0.03g; P=0.023) compared to rangers. Light hens had significantly higher metabolisable energy intake/bird/d/BWo75 (0.854±0.019 vs 0.796±0.016 MJ/g; P=0.018), net energy intake/bird/d/BW^0.75 (0.595±0.013 vs 0.551±0.012 MJ/g; P=0.032), retained energy/bird/d/BW^0.75(0.225±0.013 vs 0.181±0.012 MJ; P=0.032) and lower heat production/bird/d (0.936±0.011 vs 1.003±0.012 MJ; P=0.002) than heavier hens. In conclusion, stayers required higher maintenance energy than rangers, and light rangers are more energy efficient than light stayers. Future research on determination of ideal body weight of layers in the freerange system would be beneficial.