Influence of group size on performance and tail biting in growing-finishing pigs with intact tails.

This study investigated the effect of group size on tail damage and growth performance in growing-finishing pigs with intact tails. A total of 432 pigs were housed indoors on fully-slatted floors and assigned to either small (nine pigs per pen) or large (18 pigs per pen) groups, with equal space and resource allocation per pig. No environmental enrichment was provided. From nine to 23 weeks of age, pigs were monitored weekly for tail injuries using a 5-point scale (0 = no injury, 4 = partial or total loss). The most severe score observed during each four-week period was used for analysis, and outbreaks were defined as the occurrence of one or more pigs per pen with a tail score ≥ 2. Group size did not influence average daily gain, feed intake, or feed to gain ratio. However, pigs housed in small groups experienced more frequent and severe tail injuries, including a higher proportion of removals due to tail wounds. In contrast, pigs in large groups were more likely to receive healed tail scores (score 1) or mild injuries (score 2), and experienced fewer removals. While these results suggest that tail damage may be less severe in larger groups, the total number of pigs affected by tail biting was similar across treatments. These findings highlight the importance of managing tail-damage severity and suggest that group size can influence welfare outcomes in systems where pigs are raised with intact tails.