Utilization of Optical Flow Algorithms to Monitor Development of Tail Biting Outbreaks in Pigs

SIMPLE SUMMARY: Optical flow is a measurement of movement of individual objects in a group and can be used to monitor activity changes in both humans and animals. Using optical flow to monitor activity changes in pigs has not yet been reported. In this study, behavior of pigs in four pens of 30 pigs was video-recorded. The video-recordings before and during the first outbreak of tail biting were viewed manually to register active and resting behaviors of pigs. The same video-segments for behavioral evaluation were used for calculation of optical flow. Results indicate that mean optical flow was higher three days before and during the day of the tail-biting outbreak, suggesting increased activity level, compared to 10 days before the outbreak. All optical flow measures were correlated with time spent standing by pigs, indicating that movement during standing was associated with optical flow measures. These results suggest that optical flow measures might be a useful tool for automatically detecting activity changes associated with onset of tail-biting outbreaks. ABSTRACT: A study was conducted to evaluate activity changes in pigs associated with the development of tail-biting outbreaks using optical flow algorithms. Pigs (n = 120; initial body weight = 25 ± 2.9 kg) housed in four pens of 30 pigs were studied for 13 weeks. Outbreaks of tail biting were registered through daily observations. Behavior of pigs in each pen was video-recorded. Three one-hour video segments, representing morning, noon, and afternoon on days 10, 7, and 3 before and during the first outbreak of tail biting were scanned at 5-min intervals to estimate time budget for lying, standing, eating, drinking, pig-directed behavior, and tail biting. The same video segments were analyzed for optical flow. Mean optical flow was higher three days before and during the tail-biting outbreak, compared to 10 days before the outbreak (p < 0.05), suggesting that pigs may increase their activity three days before tail-biting outbreaks. All optical flow measures (mean, variance, skewness, and kurtosis) were correlated (all p < 0.01) with time spent standing, indicating that movement during standing may be associated with optical flow measures. These results suggest that optical flow might be a promising tool for automatically monitoring activity changes to predict tail-biting outbreaks in pigs.