EFFECTS OF LIGHT AND DARKNESS ON HEAT AND MOISTURE PRODUCTION OF BROILERS

Heat and moisture production rates of ad-libitum fed Ross x Ross broil ers (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 o f 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 degrees C and 52 +/- 5%, respectively. After a two-da y acclimation period, moisture production (MP), sensible heat producti on (SHP), and total heat production (THP) rates of the broilers were m easured at 30-min intervals for four consecutive days. MP, SHP and THP during the lighting period averaged 6.1 g H2O/(kg . h), 4.3 W/kg, and 8.4 W/kg, respectively, for the present study, as compared to the lit erature values of 6.5 g H2O/(kg . h), 4.0 W/kg, and 8.5 W/kg, respecti vely, for 2 kg broilers at 16 degrees C air temperature. MP, SHP and T HP during the dark period, not available in the literature, were reduc ed to 74%similar to similar to 76% of those for the lighting period an d averaged 4.7 g H2O/(kg . h), 3.1 W/kg, and 6.3 W/kg, respectively (P < 0.01). The result of reduced heat and moisture production for the b roilers in the dark coincided with the literature report for pullets a nd layers, although the magnitudes were different The substantial diff erences in broiler heat and moisture production between lighting and d ark periods should be considered when designing heating and cooling sc hemes for broiler houses. Far instance, variable water application rat es would be more effective than a constant application rate in cooling broilers by surface wetting under intermittent lighting conditions.