Tail-in-mouth behaviour in slaughter pigs,in relation to internal factors such as: age,size, gender,and motivational background

Tail-in-Mouth (TIM) behaviour has occasionally been observed among pigs living under semi-natural conditions. It is therefore considered to be a normal, low-frequency behaviour. Under certain conditions, TIM behaviour may increase in frequency and progress into tail biting per se. Several factors, such as age, gender, and size, are believed to enhance this development. This study aimed to elucidate the frequency of TIM behaviour among slaughter pigs, specifically in relation to age, gender, size, and group composition regarding gender. Similarly, we intended to characterize the motivational context in which TIM behaviour occurs. Two batches consisting of 24 pigs each, weighing between 40 and 50 kg, were allocated into 3 groups: 1) Eight female pigs; 2) Eight castrated male pigs; 3) Four female and four castrated male pigs (mixed-gender group). Observation was performed by video recording 4 h per day, 1 day per week, for four consecutive weeks. The pigs were weighed once a week during the experiment. The number of TIM events (counts) as well as the identity of the performer and the receiver of TIM behaviour was recorded. The results showed that the frequency of TIM behaviour in the male group was significantly lower than in the female and mixed-gender groups (P=0.003). Size expressed as weight or growth rate did not influence the amount of TIM behaviour performed or received. TIM behaviour was positively related to social exploration and environmental exploration (P<0.001). Finally, TIM behaviour was most often performed while the pigs were standing still or lying down (P<0.001).