Relationships between ranging behaviour and welfare of commercial free-range broiler chickens

Abstract

© 2017 Dr. Peta Simone TaylorFree-range chicken meat consumption has increased, partly driven by consumer perception that free-range housing is better for welfare. However, there have been few scientific investigations into the implications of ranging on broiler chicken welfare. Furthermore, how and why chickens access an outdoor range is largely unknown. Previous research has monitored broiler chicken ranging and welfare at the flock level. However, not all chickens access the range when the opportunity is provided. Subsequently, measures at the flock level may not be an accurate assessment of the implications of range use. With the advancement of technology, tracking individual chicken ranging behaviour is now possible. The research presented throughout this thesis was designed to obtain a greater understanding of the relationships between individual ranging behaviour of free-range broiler chickens on commercial farms and the relationships with welfare. Chapters Three and Four provide descriptive analysis of the environmental factors associated with ranging behaviour. Tracking individual chicken ranging behaviour showed that the proportion of the flock that accessed the range was greater than previously estimated with alternate methodologies. Range use was season dependent with fewer chickens and range visits observed in winter flocks. Heterogeneous flock ranging behaviour was considerable, including chickens that only accessed the range once (8 to 12% of tracked chickens) and high frequency ranging chickens (3 to 9% of tracked chickens) that accounted for more than one third to a half of all range visits within the flock. Chapters Five and Six investigated relationships between ranging behaviour, individual chicken characteristics and welfare. Few relationships were identified in winter flocks, which may be reflective of minimal range use. In summer flocks, lower weight, better gait scores, increased plumage cover and lower physiological stress responses prior to range access were predictive of subsequent ranging behaviour. These results suggest that individual characteristics and/or early life experience may be partially responsible for heterogeneous flock ranging behaviour. Furthermore, accessing the range was related to welfare in summer flocks after range access; including reduced fear responses and improved gait scores and cardiovascular function. The study presented in Chapter Seven, investigated relationships between distance ranged from the shed and chicken welfare. Bi-directional relationships between ranging distance and body weight were observed. Frequently ranging further from the shed was associated with improved gait scores, less hock burn, and reduced acute physiological fear responses to confinement after range access was provided. Increased foot pad dermatitis was associated with increased range visits, but not ranging distance. These results suggest that ranging further from the shed had subsequent implications for welfare. This thesis provides evidence that accessing an outdoor range has bi-directional relationships with chicken welfare. Due to the nature of the research presented in this thesis causation could not be identified. However, the research contributes to the limited knowledge of free-range broiler chicken welfare. As such, the broader understanding of ranging and welfare on commercial farms obtained through this thesis provides industry relevant, hypothesis generating evidence to aid optimal ranging behaviour on commercial farms that promotes good welfare