Effects of stocking density and group size on heat and moisture production of laying hens under thermoneutral and heat-challenging conditions

Current and relevant heat and moisture production data for laying hens are necessary for sizing and operating ventilation systems for commercial layer housing. Different stocking densities are being adopted in cage layer facilities, but there is a lack of information concerning the potential impacts of these changes on environmental control. A study was conducted with 24 groups of 48 hens (39 to 46 weeks old) to compare heat and moisture production, via indirect calorimetry, for four different stocking densities (348, 387, 465, or 581 cm ² hen ^-1; 54, 60, 72, or 90 in.2 hen ^-1) and two group sizes (8 or 16 hens per cage). Data were collected under thermoneutral (24°C or 76°F) and heat-challenging conditions (32°C or 90°F and 35°C or 95°F). No notable differences in heat and moisture production were observed among the treatments under the experimental conditions. Room-level 24 h time-weighted mean sensible heat production, latent heat production or moisture production, and total heat production, respectively, were found to be 2.8 to 3.1 W kg ^-1, 3.5 to 3.7 W kg ^-1, and 6.4 to 6.6 W kg ^-1 at 24°C; 0.7 to 1.0 W kg ^-1, 4.9 to 5.2 W kg ^-1, and 5.6 to 6.1 W kg ^-1 at 32°C; and -1.0 to -0.4 W kg ^-1, 5.9 to 6.5 W kg ^-1, and 5.4 to 5.7 W kg ^-1 at 35°C. These results imply that for existing laying hen houses, reducing stocking density, and thus flock size, will reduce the heat and moisture generated within the houses. This may lead to difficulties in maintaining desired temperatures without compromising air quality during cold weather, but reducing stocking density may offer benefits for heat stress prevention and relief during hot weather.