The Impact of Excreta/Excreta Gas Control Strategies on the Behaviour and Physiology of Laying Hens
Commercially housed laying hens are exposed to excreta/excreta gases that would not arise in their natural habitats. Limited information is available on how exposure to excreta, excreta gas, or their control strategies (fresh litter, litter amendments, and low-protein diets) impact laying hens. Therefore, this study was designed to understand the behavioural and physiological implications of exposure to excreta/excreta gases on laying hens. Four experiments comprise this thesis. The first experiment tested hens’ behavioural response to air/excreta gas mixture in a chamber and found that hens prefer fresh air over excreta gas (Chapter 3). The second experiment then assessed hens’ relative preference for using non-soiled or soiled scratch pads in enriched cages and reported more foraging in excreta-soiled compared to non-soiled pads (Chapter 4). In a consumer-demand setup, the third experiment assessed hens’ motivation to access unsoiled litter, soiled litter, soiled litter treated with an acidifier, or no litter substrate in floor pens. The outcome showed that hens possessed a relative preference for litter substrates over no litter but displayed no preference for litter (soiled/unsoiled) type (Chapter 5). Finally, the last experiment found that nitrogen-reduced diets did not impact physiology or learning ability of laying hens taught a discrimination reversal-learning task (Chapter 6). These results provide the first glimpse into how excreta and excreta-gas environments impact laying hen welfare.