Heat and moisture production rates (HP, MP) of modern pullets and laying hens were measured using large-scale indirect calorimeters that mimic commercial production settings. The experimental birds were Hy-Line W-36 strain at 1-5, 10, 21, 37, and 64 weeks of age and Hy-Line W-98 strain at 1-5 weeks of age. Total HP (THP) was partitioned into latent and sensible HP (LHP, SHP) at bird level (excluding moisture evaporation from feces) or room level (including fecal moisture evaporation from feces). The W-98 and W-36 pullets reached their metabolic peak at about 10 and 14 days of age, respectively. The W-98 pullet showed higher THP than the W-36 counterpart. Modern pullets have significantly higher THP (12% to 37%; P < 0.05) than pullets of 20 to 50 years ago. At the initial stage of egg production, the W-36 layers showed 12% higher THP than that predicted by the CIGR (1999) model, and the difference diminished with time. Evaporation of fecal moisture elevated room LHP by 8% to 38% (average 14%) during light period and by 21% to 79% (average 43%) during dark period but reduced room SHP by 4% to 17% (average 11%) during light period and by 14% to 33% (average 22%) during dark period with reference to bird LHP or SHP. All HP responses in the dark were significantly (P<0.05) reduced to various degrees (e.g., 23% to 34% for THP) as compared with those during light period. Diurnal bird and room LHP amounted to, respectively, 17% to 87% (average 47%) and 33% to 99% (average 62%) of THP for pullets and, respectively, 29% to 50% (average 39%) and 29% to 55% (average 45%) of THP for laying hens. Respiratory quotient (RQ) ranged from 0.77 to 1.18 (average 0.94) for pullets and from 0.68 to 1.02 (average 0.91) for laying hens. Regression functions that relate daily mean THP, LHP, and SHP of the bird or room to bird body mass were established. Results of this study provide an updated thermal load database for design and operation of poultry housing ventilation systems, as well as the latest bioenergetics of modern pullets and hens.

Units: SI