In-barn heterogeneity of broiler chicken welfare in two industrial house designs and two seasons in Southern Brazilian subtropical climate

Abstract

The science of animal welfare is key to improving the life quality of billions of chickens, by supporting decisions through the assessment of environmental and animal-based indicators in different conditions. Our goal was to assess the variation of bird welfare within the same barn and whether this variation depends on barn type or season. We described and compared the in-barn heterogeneity of broiler chicken welfare in four closed-sided (CS) and 13 open-sided (OS) industrial poultry houses, during two different seasons (summer/autumn and winter). The measures were divided into two categories: 1) environmental indicators: relative humidity, temperature, air velocity, ammonia (NH3) and carbon dioxide (CO2) concentrations, and illuminance; 2) animal-based indicators: contact dermatitis on the breast and abdominal areas, bird soiling, footpad dermatitis, hock burn, and lameness. The results of assessments in 30 equidistant locations, covering the whole inside area of each barn, were organized into kriging maps. Linear regression and generalized models were fitted, considering predictor variables and the interaction effect between them; the Tukey test was used for the multiple comparisons of means. We used geostatistical modelling for continuous and discrete data for environmental and animal-based measurements, respectively. In-barn heterogeneity was observed for the prevalence of environmental and animal-based problems. There was a pattern for the spatial distribution, heading from the house centre to the West end of both house types, with worse results for three environmental indicators (higher temperature, and NH3 and CO2 concentrations) and three animal-based indicators (higher prevalence of hock burn, bird soiling and footpad dermatitis). In CS, illuminance was very restrictive (4.4 to 6.7 lx) when compared to OS houses (119.8 to 145.3 lx); in both house types the prevalence of lameness was high (50.9 to 78.0%), even though both illuminance and lameness prevalence were evenly distributed inside all houses. The kriging maps allowed for the identification of worse welfare problems in the West direction, which in CS means near exhaust fans and in OS houses the direction of positive-pressure mechanical ventilation by fans. Our results show that attention is needed for the variation of bird welfare conditions inside each barn, and allow for the adoption of strategies to spread best conditions throughout the internal barn area in both house designs. Principally, the original findings on in-barn bird welfare heterogeneity suggest the relevance of constant bird welfare monitoring in key locations within the barns, minimally for the indicators with known different in-barn spatial distributions.