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For intensive livestock and poultry production in animal buildings, economic optimization techniques are needed. In this research, we investigated a relationship between the growth and production of laying hens and their thermal environment to obtain a growth and production model of layers that is based on economic optimization of environmental control for egg production.

Two groups of five laying hens, White Leghorn, were examined and confined to a cage individually in a barn. The barn was not equipped with an air conditioner, only protected from rain, wind, and solar radiation. The air temperature of one group was controlled with a heater in an adjacent room in the barn and that of the other group was not controlled. Hence the noncontrolled group was dependent on the thermal environment of the barn. The hens were raised from an age of 17weeks on Oct 26, 1995 to 47 weeks on May 29, 1996. We measured air temperature, humidity, feed intake, water intake, and number and weight of eggs daily, as well as weekly factors of waste production and body weight.

During the experiment the controlled group was kept at a thermal environment of air temperature and relative humidity; (15 C 2 C) and (42% 6%), respectively represented by (average s.d.). The non-controlled group attained an air temperature of (5 C 5 C) and a relative humidity of (68% 5%) for the entire period. During the age of 19 weeks to 47 weeks, except for two weeks at the beginning, the average daily feed intake was not different (P>0.1) between the two groups. However the average daily measurements of water intake, egg weight, waste production, body weight were greater in the controlled group. Across all ages the average feed requirement, (dividing daily feed intake by daily egg weight), was 1.97 for the controlled group and 2.04 for the non-controlled group. The feed efficiency was greater by 3.6% in the controlled group. The small gain is due to hens of the controlled group using feed energy for egg production and also weight gain. For both groups, the feed requirement decreased linearly with an increase of air temperature and was not affected by relative humidity.