Behavioral responses of laying hens to atmospheric ammonia in an environmental preference chamber

Balancing economics and animal welfare can be a challenge for environmental control for poultry buildings when the ventilation rate is reduced, which often happens during cold outdoor conditions to help maintain indoor thermal conditions. Decreased ventilation rates can result in increased concentrations of manure-derived gases like ammonia (NH₃), and NH₃ concentrations in poultry barns have been documented to exceed 100 ppm. While some previous studies have suggested that laying hens prefer NH₃ levels <25 ppm, other studies reported no similar observation. This discrepancy suggests a need to better understand how different NH₃ levels in barns affect hen, and if known, could be used to provide practical and meaningful management recommendations. Animal behavioral feedback, such as preference or aversion testing, can be a valuable tool for understanding animal welfare. Environmental occupancy and behavioral time budgeting were applied in this study to better understand bird perceptions to different levels of atmospheric NH₃. Prior to the study, hens (Hy-line W-36) were reared from age 18 to 63 weeks in one of two environments: fresh air (<5 ppm NH₃) and ammoniated (30 ppm NH₃). Sixteen hens (n=8 from each rearing environment) were tested individually in a four-compartment environmental preference chamber. Each compartment was independently controlled for different ammonia levels (0, 28, 57, and 114 ppm) during the treatment period, and a test bird was allowed to move between the compartments via interconnecting tunnels. Hens were given one day of acclimation to the chamber before treatment, followed by 24 h of NH₃ treatment, followed by another 24 h of NH₃ treatment with a shift in assigned location of each treatment based on location preference during the first 24 h of treatment. Hen behavior was recorded during the light hours via video surveillance. An ethogram was applied to each compartment that included: standing, lying, eating, drinking, grooming, and other. Behavioral data were analyzed using scan sampling (one min of observation every 30 min) with the observer blinded to treatments. Preliminary analyses revealed no effects for ammonia concentrations or prior exposure on bird occupancy, but the number of standing events was greater among birds at higher concentrations of NH₃ (p = 0.027). Overall time budget for test birds did not differ, and the birds spent the majority of their time budget eating and lying regardless of NH₃ concentrations in chamber compartments.