Abstract
Tail-biting is a persistent welfare problem in growing-finishing pigs. Identifying pigs that initiate tail-biting and understanding factors predisposing pigs to tail biting remains challenging. This study aimed to identify and characterize tail biters and compare growth, tail injury and tail biting behavior between tail biters and non-tail biters. Pigs (n = 432) with intact tails were assigned to small (9 pigs/pen) or large (18 pigs/pen) pens at 9 weeks of age and remained in the same pen until market weight at 23 weeks of age. Growth performance was measured over the 14-week study period. Tail injury was assessed weekly on all pigs using a 0-4 scale (0=no injury; 1=healed injury; 2=visible blood; 3=wounds or abscesses; and 4=tail loss). The greatest score each pig received over the study period was defined as the Maximal Tail Score (MTS). A Tail-Biting Outbreak (TBO) was confirmed when one pig in a small pen or two pigs in a large pen scored ≥ 2. Pig behavior was recorded continuously for 14 weeks using the NUtrack Livestock Monitoring System. Videos from 0800 to 1500 h on the day before the first TBO in each pen were viewed manually to record ID and sex of tail biters and victimized pigs. Tail bites per pig performed (# TB), total tail bites occurred per pen (Total TB), and tail bites per pig as a percentage of total tail bites in the pen (% Total TB = [# TB/Total TB] x 100%) were summarized using ANOVA. The top 25% of pigs in each group size for # TB and % Total TB were classified as tail biters. Tail biters in small pens performed at least six tail bites and contributed at least 20.0% of total tail bites in the pen, while tail biters in large pens were responsible for at least four tail bites and accounted for at least 10.6% of total tail bites in the pen (Table 1). Other data were analyzed using GLIMMIX Procedure with pens as the experimental unit or Frequency Procedure with Chi-square test in SAS. Initial weights did not differ between biters and non-biters; however, biters had lighter final weights (P = 0.03) and lower ADG (P = 0.02) than non-biters. Biters are predominantly gilts, accounting for 70% of the group. On average, biters were tail bitten less frequently than non-biters (P = 0.0001). No difference in MTS between biters and non-biters was detected. Results suggest that tail-biters were predominantly gilts, exhibited lower ADG and lighter final weights, and were less frequently tail-bitten than non-biters.
