PSIII-6 - Tail damage caused by tail biting in growing-finishing pigs housed in two group sizes

Abstract: Tail biting can compromise the welfare of pigs and cause economic losses for pork producers, but little is known about the development of tail biting and its resulting impact on pigs. In this study, we investigated victimization by tail biting and the resulting impacts on the welfare and performance of pigs housed in two group sizes. Pigs (n=432, initial weight=22.0 ± 3.7 kg) with intact tails were housed in large (LG=18 pigs/pen, 12 pens) or small groups (SG=9 pigs/pen, 24 pens) in a barn with fully slatted floors for 14 weeks until market weight (120.7 ± 11.8 kg). Floor space (0.76 m²/pig) and feeder space (4 feeder spaces/9 pigs) allowance were identical between group sizes, and pigs were stratified by initial weight and sex across treatment pens. Growth performance, pig removal, and tail damage were monitored throughout the study. Tail damage was assessed for each pig weekly and during tail biting outbreaks, using a subjective scoring system (0=no damage; 1=healed lesions with small scabs; 2=puncture wounds with visible blood; 3=wounds with signs of infection; 4=partial or total loss of the tail). The maximal tail score (MTS) each pig received every four weeks and over the entire 14 weeks was summarized. Pigs that received MTS of <u>></u>2 were considered victimized by a tail biter. Data were analyzed using Glimmix procedure with logit function and FREQ procedure with chi-square and CMH test of SAS software. Compared to SG, LG had greater MTS during the initial four weeks (1.1 vs. 0.8, chi-square=17.9, df=1; P< 0.001) and reduced MTS during the last two weeks (0.7 vs. 0.9, chi-square=4.8, df=1; P=0.03), suggesting that tail damage declined as pigs grew in LG, but not in SG. The number of pigs removed for tail biting tended to be less and those removed for death and sickness tended to be greater in LG than in SG (chi-square=7.4; df=3; P=0.06). Across group sizes, 68% of the removed pigs (n=28) were victimized by tail biters (MTS<u>></u>2). Between group sizes, there was no difference in time to first victimization or how often individual pigs were victimized throughout the study. Across group sizes, 45% of pigs were never victimized, but 22%, 16%, and 9% were victimized 1, 2, and 3 times, respectively. Eight percent of pigs were victimized more than three times, including 6% with MTS of 3 or 4. Pigs with MTS of 4 over the entire study period were three times more likely (odds ratios between 3.18 and 3.70; all P ≤ 0.03; Table 1) to have market weight lower than the average compared to other pigs. Based on these results, we suggest that management strategies should prevent multiple victimizations or tail loss to maintain pig welfare and performance.