Emissions of ammonia, methane and nitrous oxide from pig houses and slurry: Effects of rooting material, animal activity and ventilation flow

Animal production is subjected to frequent public debate, because of environmental problems and increasing concern on animal welfare. European Union regulations about animal welfare stipulate that pigs must have permanent access to a sufficient quantity of material to enable proper investigation and manipulation activities. However, the use of rooting materials, such as straw or maize silage, in slatted systems may influence gaseous emissions from pig houses and slurry. The objective of this work was to evaluate the effects of different factors, including: animal activity, outdoor temperature, ventilation flow, number of heat production units (hpu, where 1 hpu is equal to 1000 W of total heat produced by the animals at 20 °C), time of day and type of rooting material provided to the animals as environmental enrichment; on ammonia, methane and nitrous oxide emissions, measured in a pig building for fatteners over 37 days. In order to obtain a better understanding of the effect of the rooting material on gaseous emissions, an additional laboratory test was performed with mixtures of slurry and rooting materials stored in enclosed flux chambers, simulating the conditions during storage of slurry. 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 (R2 = 0.94) and ventilation flow (R2 = 0.79), 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 h−1 hpu−1, and a decrease in the averaged methane emission from 3.05 to 1.70 g h−1 hpu−1. In the laboratory test, ammonia emissions were significantly higher from pig slurry added maize silage (43 mg h−1 m−2) than from pig slurry added straw (3.5 mg h−1 m−2), 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.