217 Understanding tail-biting in pigs: Effects of time of day, posture, and feeder occupancy.

Abstract The objective of this study was to identify when and where tail-biting occurs and analyze pig postures to inform management strategies that reduce tail-biting and improve pig welfare. Pigs (N = 315; initial weight = 22.07 ± 3.76 kg) with intact tails were assigned to small (SG, 9 pigs/pen, 4.80 x 1.55 m) or large (LG, 18 pigs/pen, 4.80 x 3.10 m) pens, with SG having 4 feeder spaces and LG having 8 feeder spaces. Pig behavior was recorded continuously for 14 weeks using the NUtrack Livestock Monitoring System. Videos were manually viewed from 0800 to 1500 h on the day before the first tail-biting outbreak in each pen to register behavior when tail-biting occurred. Data were analyzed using the FREQ procedure in SAS. Standardized residuals (> 2 or < -2) were used to identify significant deviations in temporal distribution and feeder occupancy. Residuals of hourly tail-biting events indicated a higher-than-expected occurrence between 0800 – 0900 h (r = 3.21) and 1400 – 1500 h (r = 3.72), whereas lower-than-expected occurrences were observed between 0900 – 1000 h (r = -3.26) and 1000 – 1100 h (r = -4.36). Victimized pigs were primarily lying sternal (χ2 = 1818.06, df = 5; P < 0.0001), while pigs engaging in tail-biting were more likely to be standing compared to non-biting pigs (χ2 = 1008.6, df = 3; P < 0.0001) during tail-biting events. Tail-biting predominantly occurred in the middle of the pen rather than near the front or rear of the pen (χ2 = 24.41, df = 2; P < 0.0001). Tail-biting was more likely to occur when feeder occupancy was low, specifically when 50% or fewer of the feeder spaces were occupied, in both SG (χ² = 362.55, df = 4; P < 0.0001) and LG (χ² = 224.86, df = 8; P < 0.0001). In SG, biting was significantly overrepresented when 0 or 1 pigs were at the feeder (r = 9.70, 9.34). Pigs in LG exhibited a similar trend, with tail-biting overrepresented when 0, 1, 2, or 3 pigs were at the feeder (r = 3.0, 2.04, 6.35, 7.62). These results indicate that tail-biting occurred more frequently when victimized pigs were lying sternally in the middle of the pen during the morning and late afternoon, particularly when most feeder spaces were unoccupied. Further research is needed to validate these findings for the development of management strategies to minimize tail-biting and improve pig welfare.