Gender effects on tail damage development in single- or mixed-sex groups of weaned piglets

While extensive research on tail biting among pigs has focused on external factors (e.g., enrichment material), limited research has been conducted on internal factors (e.g., gender, breed or age), which may affect the predisposition of piglets to start tail biting. Furthermore, to test internal or external factors, most previous research used end point observations (e.g., tail damage at abattoirs). However, the potential factors causing tail biting, and the expression of tail biting itself can change over time as pigs grow older. Tail damage development over time might provide more accurate information on external and internal factors affecting tail biting than end point observation. Using tail damage development, we studied the effect of gender in single-sex and mixed-sex groups on tail biting. Tail damage development was recorded two ways: a) number of days before 40% of the piglets was observed with tail damage (40% incident point) and b) number of days a piglet was observed with tail damage (tail damage duration). A 2 × 2 factorial design was used and this resulted in four treatment categories: (1) all-male groups, (2) all-female groups, (3) males in mixed-sex groups and (4) females in mixed-sex groups. During the observation period tail damage (no damage, bite marks or tail wound) of 700 weaned piglets was scored three times per week for 32 days. Following the onset of tail biting, all-female groups had a lower 40% tail damage incident point (10.9 days), compared to the other three treatment categories (average of 16 days; P < 0.05). In all-female groups, piglets also had a higher tail damage duration (20.2 days), compared to the other three treatment categories (average of 16 days; P < 0.05). Several interactions between gender and mixing were found (P < 0.05); males in mixed-sex groups had a lower 40% tail damage incident point and a higher tail damage duration than females in mixed-sex groups. These results indicate that female piglets are more likely to tail bite compared to male piglets. Furthermore, at the end of the observation period, tail damage had developed to high levels in all groups and, at that point, differences between all-female groups and the other groups were absent. Tail damage development is therefore a better way to analyse the effects of external and internal factors that result in tail biting, compared to methods based on end point analyses.