Impact of different group sizes on plumage cleanliness and leg disorders in broilers

Abstract

The aim of the present study was to assess welfare and health parameters of broiler chickens housed in different group sizes. 6400 mixed-sex day-old broiler chicks were housed in four types of rectangular enclosures which provided 10 m2 [small], 30 m2 [medium], 100 m2 [large] and 500 m2 [very large] floor space. Per pen there were 100, 300, 1000 and 5000 birds, respectively and therefore constant density for all groups (10 birds/m2). Fifty birds per group were randomly selected as focus animals, and these birds were individually tagged to ease identification. Mortality, welfare and health parameters [gait score, hock burn, tibial dyschondroplasia (TD), foot pad dermatitis, plumage cleanliness] were assessed using scoring systems on a scale from 0 (indicating non-affected birds) to 2, 3 or 5 (indicating severely affected birds). Results for gait scores, hock burn and plumage cleanliness indicated better welfare of birds in small (except hock burn, P > 0.05) and medium sized groups, compared to very large groups (P < 0.05), and TD was more severe in very large compared to large groups, while food pad dermatitis was less severe in very large compared to medium sized groups (P < 0.05). Results of this study show that the general assumption of detrimental effects of large group sizes needs to be reassessed, especially for new commercial broilers, but further research is needed with regard to commercially relevant group sizes.