Evaluating observer agreement of scoring systems for foot integrity and footrot lesions in sheep

Both footrot and foot integrity scoring scales were more consistent within observers than between. The weighted kappa values between observers for both footrot and integrity scoring scales ranged from moderate to substantial. There was disagreement between observers with both observer bias and different thresholds between score values. The between observer thresholds were different for scores 1 and 2 for footrot (using photographs and videos) and for all scores for integrity (both walls and soles). The within observer agreement was higher with weighted kappa values ranging from substantial to almost perfect. Within observer thresholds were also more consistent than between observer thresholds. Scoring using photographs was less variable than scoring using video clips or feet.Latent class modeling is a useful method for exploring components of disagreement within and between observers and this information could be used when developing a scoring system to improve reliability.In the UK in 2004, 97% of farmers reported lame sheep in their flock with an average within flock prevalence of 10% [1]. Footrot is the main cause of lameness and foot lesions in sheep in the UK [2]. Dichelobacter nodosus is the essential organism for causing footrot, other organisms especially Fusobacterium necrophorum are thought to play an important role in the pathogenesis of footrot [3,4]. The clinical presentation of footrot is highly variable and ranges from mild interdigital inflammation (benign footrot) to under-running of horn with a characteristic smell (virulent footrot). Long term disease with footrot [3,5] and poor foot trimming [4] can alter foot integrity.A diagnosis of footrot can be made using culture or PCR from swabs taken from the hoof horn junction [6]. However, these laboratory methods are not completely reliable. D. nodosus requires complex media for culture with strict anaerobic conditions [6], and while 16S rRNA PCR is more rapid and sensitive than culture it is still far