Date of Award
Doctor of Philosophy
Agricultural and Biosystems Engineering
The laying-hen industry in the United States has been under pressure to change or modify the conventional housing systems. Traditionally, hens have been kept in conventional cages inside environmentally-controlled buildings. These cages are stacked wire mesh enclosures with mechanized egg collection, feed and water delivery systems. Over the past decade there has been much pressure to improve the welfare of the hens by replacing conventional cages with alternative housing systems. There are a number of alternative housing options under consideration or being used. In the cage free system the birds have access to the floor, but are limited to the inside of a barn. The aviary system monitored in this study is a subset of this cage-free system where a tiered structure is used to increase space allocation to the hen while accommodating more hens (than a single level barn). The aviary system also use mechanized egg collection, feed and water delivery systems similar to traditional barns. When the studies described in this dissertation were started, information on the aviary system seemed quite valuable, but the timeliness of the data has become even more apparent over the last few years. Where some states had previously been dealing with transitions to lower stocking densities (fewer hens per unit of area) or alternative systems, there is now an agreement on the table that may bring this transition to a national level.
Because the aviary system is so different from conventional housing, there are questions about the impact and performance of such a system. The most obvious difference in all alternative housing, including aviaries, is the lower stocking density. With the lower stocking density, there are many questions about the correct management of houses, especially in winter. The potential issue with ventilation for indoor air quality at the lower stocking density is the possible need for supplemental heat and its proper distribution in the house. This dissertation looks at this issue from many different angles including ventilation rate, indoor air quality, heat and moisture production of the birds, fuel usage, and the birds' preference for winter temperature-ammonia combinations. With the lower stocking density there is also a concern that the labor and utilities provided on a per bird basis will be higher. Another concern with the systems is that a portion of manure from the birds is held in the house on the floor as litter. The litter on the floor impacts indoor air quality. The ammonia and dust concentrations and emissions were two of the major concerns with regard to the litter. With the aviary system, the birds have the ability to be more active. There are questions about how this activity level impacts the heat and moisture production rates of these birds. Overall, there is very little information on the aviary system in the United States. This dissertation aims to address these questions and concerns.
Morgan Davis Hayes
Hayes, Morgan Davis, "Environmental and energy assessment of an aviary laying-hen housing system in the Midwestern United States" (2012). Graduate Theses and Dissertations. 12601.