The effect of removing animals for slaughter on the behaviour of the remaining male and female pigs in the pen

The study was performed to investigate changes in the behaviour of male and female pigs when one or more pigs were removed from the pen and sent to slaughter. Twelve pens were included, half of them housed six female pigs each, while the other half housed six male pigs each. Skin lesions and behaviour were recorded on two occasions, four days before and two days after one or more animals per pen were sent to slaughter. On the first occasion the male pigs fought on average about twice as often as the females (2.6 vs. 1.0 per animal per hour) and had twice as many skin lesions (6.7 vs. 3.2). On the second occasion, the frequency of fighting among both males (6.8) and females (1.8) had increased, however, more in males than in females. The number of skin lesions was not significantly higher on the second occasion. In the male group there was also a tendency towards increased mounting on the second occasion (from 2.3 to 3.3 per animal per hour). The study shows that the very common practice of slaughtering pigs from one pen over more than one occasion results in an increase in unwanted behaviour. The effect is more pronounced in groups of entire male pigs than in groups of females.