Intact-tail and tail-biting in Switzerland: a retrospective study Tail-biting is abnormal behaviour which can be triggered by many factors, such as a lack of enrichment material, unfavourable environmental conditions, an unbalanced diet, and poor health. This study assessed changes in feeding behaviour during an outbreak of tail biting in a feed-efficiency study. Seventy-two castrated male pigs (110.0 ± 10.7 days old; 43.0 ± 9.2 kg) were group housed in a 78 m2 pen with straw in racks and sawdust on the floor. Pigs had restricted feed access (80% of assumed ad libitum) distributed via 7 individual automatic feeders. Dietary crude protein and essential amino acids were limited to 80% of the Swiss recommendations. Two months after the start of the study (i.e. pigs at 20 kg BW) a tail-biting outbreak occurred. To better understand the reasons for this outbreak, feeding behaviour (e.g., consumption time, number of visits to the feeder, daily feed consumption, average daily gain, feed efficiency) was analysed. The retrospective study was divided into 3 phases of one week each: phase A, before tail lesions appeared; phase B, acute; and phase C, when tail-biting disappeared after restoring ad libitum feeding and removing the tail-biting trigger. The number of visits to the feeder decreased during phase A (p<0.001), reached a minimum during phase B (p<0.001), and increased during phase C. Consumption time (for a given amount of feed eaten) decreased while the tail-biting outbreak evolved (phases A and B) and remained low during phase C. These results could indicate a putative increased level of stress. Thus, one can conclude that feeding behaviour traits may be potential precursor indicators of tail-biting outbreaks.