Optical flow, behaviour and broiler chicken welfare in the UK and Switzerland

Abstract

Although systems for automated assessment of broiler chicken welfare have now been developed on a small scale, none are currently in widespread commercial use. We addressed this gap between research and uptake by field testing a camera system that uses the optical flow patterns made by the movements of flocks to monitor bird welfare. We tested the hypothesis that the movement patterns made by flocks of broiler chickens are correlated with two key welfare outcomes – mortality and hockburn. Life-long CCTV monitoring was carried out on 74 commercial broiler flocks (UK = 31; Switzerland = 43) and the resulting data analysed to give daily values of 4 optical flow descriptors: mean, variance, skew and kurtosis. Flock mortality and hockburn data were obtained from information routinely collected on the farms and at abattoirs. Bayesian multivariate regression models were used to analyse data with all 4 optical flow descriptors as input variables, first day-by-day and then cumulatively using information from each day and all previous days. For both the UK and Swiss flocks, the cumulative regression showed that optical flow was significantly (p < 0.01) correlated with % total mortality (by day 1 for the UK flocks and by day 4 for the Swiss flocks). Optical flow was also significantly (p < 0.01) correlated with % birds with end-of-life hockburn (by day 3 for UK flocks and day 2 for Swiss flocks). This ability to distinguish between flocks that will have different final welfare outcomes when the birds are only a few days old is a particularly useful property of this system as it potentially provides farmers with an early warning of problem flocks that are still young enough for interventions to be possible. In conclusion, the optical flow patterns made by the movements of broiler chicken flocks were reliably correlated with two key welfare outcomes - mortality and hockburn - obtained by cumulating information over days as the birds grow. Differences between flocks became apparent within the first few days of life and were similar in the UK and Switzerland, despite differences in environment and management practices, suggesting that this approach to automated welfare assessment has the potential for widespread commercial use.