Relationship between cattle stocking density and NH3 emissions from cattle housing

This study aims to assess the influence of livestock density on NH3 emissions from cattle housed on a straw-bedded system. The study was conducted at IGER, North Wyke, England, UK, using a system of polytunnels designed specifically for measuring gaseous emissions from housed cattle. To achieve different livestock densities, the floor area within each of the four polytunnels was kept constant and the number of animals housed was varied. Beef heifers (Red Devon, weight range 350-500 kg) were used in the trial with either 3, 4, 5 or 6 housed per polytunnel, achieving area allowance per animal of 11.7, 8.8, 7.0 and 5.8 m2 (treatments SD1, SD2, SD3 and SD4), respectively, all of which comply with the current minimum welfare standard. Mean emission rates per treatment for each of the four housing periods were in the range 1.2-6.6 g/lu/d NH3-N (where lu is livestock unit = 500 kg liveweight). Mean emission rates over the entire housing period were not significantly different between stocking density treatments (P>0.1), whether expressed on a per liveweight basis or on a per m2 floor area basis. The results from the present study would indicate that for a given straw use, increasing livestock density can reduce NH3 emissions. However, there may be interactions between the effects of straw use per animal and straw use per floor area and further study combining these treatments would be beneficial in producing recommendations for optimal livestock density and straw use. Additionally, baseline data are required on current commercial practices regarding stocking densities and straw use for beef cattle housing.