Degree of synchrony based on individual observations underlines the importance of concurrent access to enrichment materials in finishing pigs

Pigs are sociable animals with a strong motivation to explore and forage, and it has been stated that they have a strong motivation to do so synchronously. We examined the synchrony of exploration in groups of finishing pigs when enrichment materials were offered. We used a novel measure of relative synchrony for which no artificial threshold for synchrony was needed and which takes into account detailed individual data for calculating expected random synchrony.One hundred and ninety-two growing pigs were housed in groups of six animals in pens with partly-slatted floors. In two experiments, four enrichment materials each were tested one at a time and, for a given group of pigs, the material was changed every three weeks. Half of the groups were fed twice daily in a restricted manner, the other half ad libitum. Exploratory behaviour directed to the material and to the pen was scored. Relative synchrony was calculated as the observed divided by the expected synchrony for two, three, four, five and six pigs behaving synchronously. The expected synchrony was calculated using the daily individual data of each pig. Data were analysed using linear mixed-effects models.Results showed that relative synchrony for combined exploration (exploring material or pen) monotonously increased with increasing number of animals behaving synchronously in both experiments and reached above-chance values of synchrony at three to four animals. A similar pattern was found for exploring cut straw as litter with maize and cut straw as litter: synchrony increased with the number of synchronously exploring pigs to above-chance values of synchrony for four and more pigs. Relative synchrony for exploring a straw block decreased with increasing number of animals exploring synchronously with all values of synchrony below chance level. Relative synchrony increased for all the other materials (straw rack, chopped straw, chopped Miscanthus giganteus, pellet dispenser, bark compost) for up to three to four animals exploring synchronously. For higher numbers of animals, relative synchrony decreased. Above-chance values were reached at three to four animals.In conclusion, finishing pigs seem to have a strong motivation to explore synchronously in groups of up to six animals. If enrichment material is available and accessible to all animals, they will direct their behaviour to that material, whereas they redirect exploration behaviour to pen structures to achieve a high level of synchrony if access to enrichment material is restricted. The method of calculating relative synchrony based on individual observations and for any given number of animals in a group proved useful.