Tonic immobility and emergence time in pigs - more evidence for behavioural strategies

The aim of this study was to further investigate the link between tonic immobility (TI) in pigs and active/passive behavioural strategies. Twenty-nine female and entire male pigs were subjected to a series of tests at the age of 3 weeks. Individual pigs were tested for their latency to emerge from a box and this was followed by a tonic immobility test. This procedure was carried out on four consecutive days. The behaviour of the pigs on day 1 differed from the behaviour on the other test days in that the emergence time was shorter(p < 0.01), and in that pigs looked out of the box less frequently before leaving it (p < 0.01). Emergence times on days 2-4 were correlated, but not with the emergence time on day 1. Pigs tended to be less resistant to TI on days 3 and 4 than on days 1 and 2. Pigs who did not become immobile in the TI test on day 1 had significantly shorter emergence times on that day than pigs who did become immobile(p < 0.01). There were no other significant relationships between TI and emergence test behaviour. It is suggested that the link between TI and emergence time on the first test day reflects an underlying tendency to bring about change more or less quickly when faced with a challenging situation. These situations may therefore reveal differences in the active/passive dimension of personality. (C) 1999 Elsevier Science B.V. All rights reserved.