Ammonia emission from aviary housing systems for laying hens : inventory, characteristics and solutions

The development and practical application of welfare friendly aviary housing systems for laying hens, that generally emit more ammonia per hen than battery cage housing systems, would conflict with the Dutch policy to substantially reduce the total emission of ammonia from animal husbandry.This thesis describes the knowledge assessed by research on the ammonia emission levels of various types of aviary houses for laying hens (the inventory), the processes and factors involved in the kinetics of this ammonia emission (the characteristics) and the development of technical solutions which will lower the emission (the solutions).Housing systems for laying hens are described as and classified into <em>battery cages</em> and <em>alternative systems</em> . The waste resulting from the fresh droppings in these two types of housing systems for laying hens are classified as <em>slurry</em> , <em>dry manure</em> or <em>litter</em> . The degradation of nitrogenous components and the volatilisation of ammonia to the air are influenced by the manure composition, the process conditions and the local climate above the manure. Levels of emission from housing systems for laying hens vary strongly due to influencing factors that are related to <em>the housing type</em> , <em>the animal</em> , <em>the climatisation</em> or <em>the management</em> .The distribution of droppings over the two sources of emission in aviary houses, being the manure on the belts and the litter on the floor, was investigated under experimental circumstances. The effects of manure and litter handling and litter composition, and the effect of the physical parameters of the air on the emission of ammonia were quantified. The physical and chemical relationships of the volatilisation of ammonia from litter of various commercial aviary houses and the degradation of organic material in litter to ammonia were verified and demonstrated the great impact of the dry matter content of litter on the emission.A litter drying system in a Tiered Wire Floor aviary housing system was developed and the effect it had on the composition of litter and the emission of ammonia was investigated. With the knowledge acquired about the physical relationships of water evaporation from litter and the water input load to the litter through fresh droppings, it is possible to control the ammonia emission from the litter by influencing its dry matter content.