SELECTION OF MATING PARTNERS IN BOARS AND SOWS UNDER MULTI-SIRE MATING

The sexual behaviors of pigs were observed at a commercial farm to study the selection of mating partners in boars and estrous sows under multi-sire mating. In Experiment 1, three sire groups and nine sow groups were used to characterize the courtship behavior between boars and sows. The flow diagram of the behaviors constructed by sequence analysis revealed that 'nosing' by boars played an important role to induce sows to stand still, which in turn motivated boars to mount. In Experiment 2, two sire groups and four sow groups were used. Each sire group consisted of three Duroc boars raised from the same litter. Each sow group consisted of eight crossbred sows in which estrus had been induced. Each sire group was assigned to a sow group for 48 h, and their sexual behaviors were recorded continuously with an infrared camera connected to a time lapse video recorder. The same procedure was repeated 3 months later with the same sire groups and different sow groups, which made two observations per sire group. Time spent on courtship behavior with each sow varied significantly (P < 0.001) within each set of three boars. The boars spent longer times on courtship behavior and mounted and copulated more frequently with some specific sows than with others. The dendrogram constructed, based upon the time spent on courtship behavior between a sow and a boar, showed that boars and sows had a tendency to select mating partners and that some boars received more attention from sows than others. The cell by cell test on the number of mounts from boars to sows indicated that each boar had a favorite mate or mates (P < 0.05). It is likely that selection of mating partners exists between boars and sows in estrus.