Contribution of carbon dioxide (CO2) production from manure or litter can be significant relative to animal metabolic CO2 production in housing systems with less frequent excretion removal. Such CO2 contribution should be accounted for in order to improve the accuracy of estimating building ventilation rate (VR) and animal bioenergetics based on CO2 mass balance. The objective of this study was to investigate the thermal conditions (temperature and relative humidity, or RH), production, moisture content (MC), and CO2 production of laying-hen manure on collection belts and on litter in an aviary house. Hens spent about 15.25 h day-1 in the aviary colony where their manure was deposited on the belts, and the remaining 8.75 h day-1 on the litter floor where manure was deposited on belt or litter. Manure belts were operated 1/3 of their length each day.

Results show that temperature and RH were, respectively, 1.8 ± 9.3˚C (mean ± standard deviation) and 79 ± 14% for ambient air, 18.5 ± 1.7˚C and 76 ± 16% for air near manure on belt, and 19.8 ± 1.5˚C and 80 ± 17% for air near the litter. The overall daily manure production was 35.8 ± 1.4 g hen-1 day-1 on dry basis, with 90.9% deposited on manure belt and 9.1% on litter floor. MC of manure on belt was 66.4 ± 5.8%, which was significantly higher than 14.6 ± 2.4% for the litter. The combined moisture production from manure on belt and litter was estimated to be 22.6 g day-1 hen-1. The CO2 production from as-is manure was 0.10 ± 0.06 ml s-1 kg-1 (or 0.32 ± 0. 20 ml s-1 kg-1 on dry basis), whereas CO2 production from as-is litter was much lower, 0.02 ± 0.02 ml s-1 kg-1 (or 0.03 ± 0.02 ml s-1 kg-1 on dry basis). Without litter removal, CO2 production from manure and litter could amount to as high as 8.1% of the hen’s respiration CO2 at 60 week of age. This potentially significant contribution should be considered when estimating VR or animal bioenergetics using CO2 mass balance method in aviary housing systems.