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

Current and relevant information regarding heat and moisture production (HMP) of laying hens is important for design and operation of ventilation systems for commercial layer housing. Different stocking densities are being adopted by the cage layer industry, 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 HMP, via indirect calorimetry, for four different stocking densities (348, 387, 465, or 581 cm²/bird; 54, 60, 72, or 90 in²/bird) and two group sizes (8 or 16 birds/cage). Data were collected at 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 HMP were observed among the treatments under the experimental conditions (2.8 to 3.1, 3.5 to 3.7, and 6.4 to 6.6 W/kg 24-h time weighted mean room-level SHP, LHP or MP, and THP, respectively, under 24°C; 0.7 to 1.0, 4.9 to 5.2, and 5.6 to 6.1 W/kg under 32°C; and -1.0 to -0.4, 5.9 to 6.5, and 5.4 to 5.7 W/kg under 35°C). The results imply that for existing laying-hen houses, reducing stocking density and thus flock size may lead to difficulties maintaining desired temperatures without compromising air quality during cold weather, but may offer benefits for heat stress prevention and relief during hot weather.