Environmental changes due to hen spatial distribution in cage-free systems: A preliminary study

This study aimed to evaluate hen distribution and changes in environmental conditions within a multi-tiered aviary system, considering the effects of tier height and hen genotype. Additionally, the relationships between hen distribution and environmental conditions were assessed. Environmental variables, including CO2, NH3, and particulate matter (PM1, PM2.5, PM4, PM10), as well as hen distribution at the different levels, were monitored at three heights, i.e., ground floor (10 cm), midtier (180 cm), and upmost tier (270 cm). Data were collected in winter over a three-week period (31 to 33 weeks of hen age) in two aviary pens (225 hens per pen), each housing a different genotype (white or brown; Novogen Layers). Hen distribution (% of observed hens through video-recordings) was influenced by genotype, with a higher proportion of white hens observed on the mid-tier (13% vs. 8%; P<0.001) compared to brown hens, while a lower proportion of white hens were observed on the ground floor (26% vs. 28%; P<0.05). Environmental conditions changed with genotype and tier height. Higher air values of CO2, NH3, PM2.5, PM4, and PM10 (ranging from +9% to +38%; P<0.001) were recorded in the pen with brown hens compared to the pen with white hens. Then, significantly higher CO2 and particulate matter (ranging from +17% to +48%; P<0.001) were observed on the mid-tier compared to the upmost tier and ground floor, whereas NH3 concentration were highest on the ground floor (+53%; P<0.001) compared to the tiers. The concentrations of CO2 and NH3 showed weak correlations with hen distribution on the ground floor (r = 0.16; P<0.05) and at the tiers (−0.09 < r < −0.28; P<0.05). In contrast, concentrations of PM2.5, PM4, and PM10 were moderately correlated with hen presence on the ground floor (r = 0.37; P<0.001) and mid-tier (−0.43 < r < −0.40; P<0.001), while weaker correlations were found at the upmost tier (−0.29 < r < −0.25; P<0.001). In conclusion, hen genotype and tier height significantly influenced hen distribution and environmental conditions within the aviary. Brown hens showed a preference for the ground floor, where higher NH₃ concentrations were recorded, while white hens primarily occupied the aviary tiers. Elevated levels of CO₂ and particulate matter were observed in the midtier. Research supported by the European Union Next-GenerationEU (PIANO NAZIONALE DI RIPRESA E RESILIENZA (PNRR) – MISSIONE 4 COMPONENTE 2, INVESTIMENTO 1.4 – DD 1032 17/06/2022, CN00000022).