Nursing behaviour in lactating sows kept in isolation, in acoustic and visual contact

Synchronization of nursings occurs between domestic lactating sows housed in one room. This study tested experimentally whether acoustic contact without any possibility to see other sows is sufficient for a high level of nursing synchronization. Secondly, the study investigated whether the possibility to synchronize with other sows affects positively the frequency of nursing, the frequency of milk ejection and the growth rate of sucking piglets. Eleven sets of three lactating sows were observed. One sow of each set (the I sow) spent lactation in an isolated room while the other two were housed in a room with other lactating sows, one of them with acoustic and visual contact with other sows (the C sow), the other in acoustic contact only (the S sow). Nursing behaviour was recorded in these focal sows (n = 33) for 6 h on days 7 and 21 of lactation. The S sows had 43% of their nursings synchronized with the C sows (p < 0.0001 above chance) while the I sows were not synchronized above chance with either C or S sows, thus proving that audition alone was sufficient to create high synchronization of nursing behaviour. The C and S sows that had the opportunity to synchronize did not have either higher nursing frequency or higher nursing success (measured as the proportion of nursings with milk ejection) than the I sows. Also, the piglet weight gain was not different between the three types of sows. In conclusion, audition is sufficient for high levels of nursing synchrony but the mutual adjustment of behaviour that necessarily occurs during such synchronization did not cause the sows to nurse more frequently or deliver milk more frequently.