Effects of Light and Darkness on Heat and Moisture Production of Broilers

Heat and moisture production rates of ad-libitum fed Ross x Ross broilers (averaging 6.5 weeks of age and 3.0 kg of body mass) subjected to a lighting cycle of 8 h light and 4 h darkness were measured by using indirect calorimeters. The experimental broilers were kept in groups of 24 birds on litter floors with a stocking density of 0.1 m 2 /bird. Air temperature and relative humidity inside the calorimeter chambers were 24 ± 0.25°C and 52 ± 5%, respectively. After a two-day acclimation period, moisture production (MP), sensible heat production (SHP), and total heat production (THP) rates of the broilers were measured at 30-min intervals for four consecutive days. MP, SHP, and THP during the lighting period averaged 6.1 g H 2 O/(kg.h), 4.3 W/kg, and 8.4 W/kg, respectively, for the present study, as compared to the literature values of 6.5 g H 2 O/(kg.h), 4.0 W/kg, and 8.5 W/kg, respectively, for 2 kg broilers at 16°C air temperature. MP, SHP, and THP during the dark period, not available in the literature, were reduced to 74%∼76% of those for the lighting period and averaged 4.7 g H 2 O/(kd.h), 3.1 W/kg, and 6.3 W/kg, respectively (P < 0.01). The result of reduced heat and moisture production for the broilers in the dark coincided with the literature report for pullets and layers, although the magnitudes were different. The substantial differences in broiler heat and moisture production between lighting and dark periods should be considered when designing heating and cooling schemes for broiler houses. For instance, variable water application rates would be more effective than a constant application rate in cooling broilers by surface wetting under intermittent lighting conditions.