Acoustic-reward learning as a method of reducing the incidence of aggressive and abnormal behaviours among newly mixed piglets

The aim of the study was to use acoustic reward learning as an approach to reduce the incidence of aggressive and abnormal behaviours in pigs reared in intensive conditions. In one experimental round four litters of 25-day old piglets (BHZP breed) were trained over eight days to create an association between a sound and a sweet reward. The training was carried out five times per day using an electronic dog feeder which generated an acoustic signal 2s before the reward was released. A total of 5 experimental rounds were carried out. After the training period, at the age of 35 days, the piglets were weaned and mixed in two pens, 12 piglets per pen. Immediately after mixing and 24 h later, the animals were directly observed for 3 h by two trained persons (one per pen) hidden behind a transparent blind. They released the sound signal and feeder when aggressive or abnormal behaviour started. A total of 616 aggressive acts and 31 incidences of ear biting were identified, of which 52.4% in total could be interrupted by the acoustic reward treatment. The piglets' response to the feeder sound differed significantly between experimental days (P<0.001). On the second day of mixing the feeder sound made the piglets interrupt 74.9% of aggressive events, compared with only 33.7% on the first day. The type of aggression and the point in time during the aggressive action significantly influence the effectiveness of the acoustic reward treatment (P<0.001). The results show the potential for distracting piglets from specific aggressive behaviours such as head thrust (odds ratio =0.43), jumping on other pigs (0.56) or attack with bite (0.61). Ear biting was very unlikely to continue (0.55). The risk of continuing elevated aggression level behaviours was doubled in the event of chasing (2.16) and the risk that fighting would continue after the feeder sound was released was seven times higher (7.89). The results suggest that acoustic reward treatment can reduce aggression and ear biting in piglets.