Animal houses are an important source of ammonia (NH3), methane (CH4) and nitrous oxide (N2O) gases that can have negative consequences for people, animals and environment. These gases are produced inside the buildings by direct emission from the digestive system of the animals or from the decomposition of the animal wastes. The produced gases are subsequently volatilized, and emitted to the outdoor environment by the ventilation. Many different factors can influence gas formation and volatilization and so, gaseous concentrations and emissions from animal houses. These factors are mainly related to: animals (e.g. genetics, diet, number and weight, animal activity, and behaviour), wastes (e.g. handling, treatment, pH, temperature, and surface area), environment (e.g. indoor and outdoor temperature, ventilation flow, and air velocity over the manure surface) and other site-specific factors. Regarding these site-specific factors, the presence of certain materials inside of pig barns, used either as bedding material or for any other purpose, can have an effect on the emission of gases (Monteny et al., 2006; Sommer et al., 2006). This effect is partly due to the fact that during storage most organic solid materials (including the rooting materials that fall through the slats to the slurry pit in slatted houses) float to the surface of the slurry forming a crust layer. This crust layer can decrease the wind speed over the slurry, resulting in reduced transport by convection, higher levels of gases above the free surface of the slurry, and lower gas escape. It can also contribute to a reduction in pH in the surface of the slurry. Therefore, the objectives of this work were to evaluate the influence of animal activity, indoor, outdoor and slurry temperature, ventilation flow, number of heat production units (hpu, where 1 hpu is equal to 1000 Wof total heat produced by the animals at 20 8C) and time of day (day or night) on NH3, CH4 and N2O emissions, measured in a pig building for fatteners over 37 days. Another objective was to study the effects of the type of rooting material provided to the animals on gaseous emissions, from data collected in two experiments: the 37 days field experiment in the pig building, and a laboratory test carried out with different types of rooting materials added to slurry in enclosed flux chambers, simulating the conditions during storage of slurry. It was concluded that in the pig building, the three parameters that explained most of the variability of ammonia and methane emissions were type of rooting material, animal activity, and ventilation flow. The diurnal variations of ammonia and methane emissions were highly correlated with the diurnal variation of animal activity and ventilation flow, respectively. The change of the rooting material, from maize silage to straw, caused an increase in the averaged ammonia emission from 1.68 to 2.22 g hˉ¹ hpuˉ¹, and a decrease in the averaged methane emission from 3.05 to 1.70 g hˉ¹ hpuˉ¹,. In the laboratory test, ammonia emissions were significantly higher from pig slurry added maize silage (43 mg hˉ¹ mˉ²) than from pig slurry added straw (3.5 mg hˉ¹ mˉ²), while no significant differences were found concerning methane emissions. This work revealed that the use of rooting materials as environmental enrichment for improving the welfare of growing finishing pigs has an effect on ammonia and methane emissions from pig houses. The evaluation of this effect has to be done under normal housing conditions including presence of animals in the barn.

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