Gaseous emission from alternative housing systems for laying hens

Laying hen housing systems imposed by the 99/74/CE Directive are conceived to improve welfare of laying hens, so they could express natural behaviours, such as bitter-scratching, dust-bathing, egg-laying on nests. However, recent researches on enriched cage systems and deep-litter systems pointed out some negative aspects, like a worse egg quality, because a lot of eggs are laid out of the nest and are frequently broken. The Department of Agricultural Science and Environment, University of Udine, in the frame of a research project co-financed by the Ministry of University and Research, carried out several experimental trials in alternative houses with deep-litter system in order to assess the environmental impact. Egg production from alternative houses was similar to that generally obtained from conventional cage systems, but hygienic, behavioural and management problems were pointed out. In alternative houses, higher ammonia and dusts concentrations were found, distressing hens, workers and environment. Ammonia emissions, calculated from gaseous concentrations and ventilation rate, ranged from 0.239 and 0.427 kg hen-1 year-1. According to the Best Available Techniques reference document of the IPPC EC Directive (ILF BREF, 2003), the deep litter systems for non-cage housing of laying hens could not be classified as BAT, due to the high emission levels.