Effects of simulated lairage conditions on the physiology and behaviour of pigs.

The responses of pigs to being driven and mixed together in lairage were investigated. Five groups of six and five groups of seven 70 kg pigs were transported for 40 minutes on a lorry and then subjected to one of the following treatments: two groups were driven down a passage; four groups (A to D) were mixed together for one hour (A and B together, and C and D together); and, four groups were driven down the passage and then mixed ('combined treatment'). The pigs' behaviour was recorded, skin damage was scored and saliva samples were taken for analysis of cortisol. The initial journey increased the pigs' salivary concentration of cortisol. Their behaviour while being driven was not correlated with the concentrations of cortisol after they were driven and cortisol concentrations did not increase relative to post-transport levels. The frequency and duration of fighting when they were mixed were positively correlated with their level of aggression in the home pen and with the increase in concentrations of cortisol when they were mixed. One hour after they had been mixed, the concentrations of cortisol had decreased relative to post-transport levels. After the combined treatment, the correlations observed for the mixing treatment were absent, and the concentrations of cortisol increased relative to post-transport levels. Skin damage was greatest after the groups of pigs were mixed. The responses observed indicate that the combined effects of driving and mixing, which are very common in lairage, were greater than the effects of driving or mixing alone.