Maintaining comfortable thermal environments and good indoor air quality is essential to ensuring optimal production performance, welfare, and health of animals. Alternative laying-hen housing systems are being adopted by some egg producers in the U.S. However, information on indoor thermal and aerial environments of such alternative housing systems is meager. This article reports a one-year monitoring of thermal conditions (air temperature and relative humidity or RH) and ammonia (NH3) concentrations and emissions of four aviary laying-hen houses (same dimensions, manure belt plus litter floor systems, 50,000-hen capacity each) at a commercial farm in the Midwest U.S. Carbon dioxide (CO2) concentrations at the air inlet and near the exhaust fans were measured and used, along with literature values of the metabolic rates of the hens, to estimate building ventilation rate (VR). The results show that indoor temperature, RH, CO2 concentration, NH3 concentration, and VR of the four houses (mean ±standard deviation) were 23.4°C ±0.3°C, 64% ±3%, 1520 ±87 ppm, 5.2 ±0.4 ppm, and 4.5 ±0.6 m3 h-1 hen-1, respectively. The highest daily mean NH3 concentration was 13 ppm (and 20 ppm within the day) in winter. The NH3 emission rate was 0.14 ±0.01 g d-1 hen-1. These values of NH3 concentrations and emissions were lower than those reported for European aviary houses. The NH3 emissions of the monitored aviary houses in this study are comparable to those of U.S. manure-belt cage houses, but are much lower than those of U.S. high-rise cage houses. The magnitude of NH3 emissions observed in this study was consistent with that of similar aviary houses with brown hens in another extended field measurement in the same region.
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