Effects of animal/feeding-place ratio on the behaviour and performance of fattening pigs fed via sensor-controlled liquid feeding

Sensor feeding is a liquid feeding system for fattening pigs that is run with a restricted animal/feeding-place ratio (AFR). Feeding occurs at specific periods, so that the trough is left empty in-between. Therefore, it must be regarded as an ad libitum feeding system. The aim of the present study was to quantify the effect of three different AFRs (4:1, 7:1 and 13:1) with nine, six and three feeding places per group, respectively, on the behaviour and performance of fattening pigs (25–100 kg) housed in groups of 40 individuals. Each AFR was tested with seven groups (21 groups in total). With each group, four pigs were selected from each weight class (lightweight, middleweight and heavyweight) as focal animals. The behaviour in the feeding area was observed by means of 24 h-video-recording for the 12 focal pigs at an age of 14 and 17 weeks. Daily weight gain was calculated for all animals. As the AFR increased, feeding bout duration at the trough declined significantly (p < 0.001), whilst the duration of waiting increased (p < 0.001). The AFR had no significant effect on the frequency of aggressive displacements at the feeding trough. On the other hand, the fatteners were more frequently pushed away from the trough without aggressive interactions as the AFR increased (p < 0.001). Besides the AFR, the age and weight class of the focal pigs had a significant effect on behaviour. Lightweight animals waited longer for access to the trough and were more often displaced from the trough as a consequence of aggressive interactions. Weight gain was lower as AFR increased (p < 0.001), an effect that was more pronounced in lightweight focal animals (p < 0.001). In conclusion, the AFR has a decisive influence on the behaviour and performance of fattening pigs fed by sensor feeding. Lightweight pigs, most likely the subordinate group members, are more affected by an increased AFR, and hence most at risk of impaired welfare. An AFR of 13:1 has marked negative effects on the pigs’ performance and behaviour and is inadvisable to be used for this feeding system.