Reliability of indicators of sheep welfare assessed by a group observation method

Assessments of animal-based outcomes form the core of routine veterinary clinical examinations and are being increasingly used as indicators of animal welfare. A method of group observation that did not require gathering and handling of individual sheep, was used to assess eight animal-based indicators of sheep welfare: demeanour, skin irritation, wool loss, excessive panting, coughing, lameness, and cleanliness of the ventral abdominal and 'breech' (perineum/gluteal/caudal hindlimb) areas. The inter-observer reliability of two or three observers who independently assessed these indicators was tested on 2406 adult sheep and growing lambs across 36 farms and the intra-observer reliability of an experienced, veterinary assessor--the 'test standard observer'--was assessed on 88 adult sheep during four on-farm assessments. Observer reliability was evaluated using Cronbach's alpha (α) comparison of the recorded proportion (%) of sheep affected by each welfare condition and by binomial logistic regression modelling. High levels of inter-observer reliability were identified for the assessment of group lameness (α 0.76-1.00) and cleanliness of the breech area (α 0.97-1.00). Excellent intra-observer reliability was determined for lameness (α 0.99), cleanliness of the breech area (α 0.97), demeanour (α 1.00) and wool loss (α 1.00). In addition, proportion data and logistic regression models identified few between-observer differences. The results suggest that welfare outcomes based on observations of the behaviour and physical appearance of individual animals within a group may offer a reliable and feasible measurement tool for the on-farm assessment of sheep welfare.