Optical flow patterns in broiler chicken flocks as automated measures of behaviour and gait

The aim of this study was to test the hypothesis that valuable on-farm outcome measures of broiler (meat) chicken welfare can be derived from optical flow statistics of flock movements recorded on video or CCTV inside commercial broiler houses. ‘Optical flow’ describes the velocity of image motion across an eye or camera and statistical patterns can be derived automatically and continuously throughout the life of a flock. We provide descriptive statistics (mean, variance, skewness and kurtosis) of optical flow of 10 intensively housed commercial broiler flocks between the ages of 32 and 35 days. There were no significant correlations between any of these measures and flock mortality. However, all four measures were correlated significantly with the % of birds in a house showing poor walking (high gait scores). Furthermore, these gait scores were highly negatively correlated with the % of time chickens spent walking and with their stride rate (no. of strides/min), as measured by focal behaviour analysis of individual birds from the same video records. The results suggest that optical flow measures have the potential to be used as an adjunct or even a substitute for gait scoring on commercial farms with the added advantage that the measurements could be made continuously throughout the life of a flock, are fully automated, completely non-invasive and non-intrusive and do not involve the biosecurity risk of having people visiting different farms to carry out gait scoring. The correlations between gait scores and optical flow also suggest that gait scoring itself has an objective basis.