Effects of neonatal castration on social behaviour, human–animal relationship and feeding activity in finishing pigs reared in a conventional or an enriched housing

Abstract

Raising entire males is already common in a few European countries. It has the advantage of avoiding the pain of castration. Entire males have also a better food conversion. However, they would be more aggressive than castrates which causes welfare troubles. The consequences for human–animal relationship are not clear. We thus wanted to determine the effects of raising entire males in stable groups compared to castrated males on their social behaviour (including agonistic behaviour, non-agonistic behaviour, play, belly-nosing), the human–animal relationship and the feeding behaviour during the fattening period. We also determined the effects of an enrichment of the housing (space, outdoor run, straw) on the same behavioural activities. Eighty males (groups of 10) were studied: 40 castrated (surgically) at 5–6 days of age and 40 left entire, half of each reared in a barren (1m2/animal, slatted floor) and half in an enriched (2.5m2/animal, straw bedding and outdoor run) housing. We observed their social activity by continuous sampling three times a month for 1h from 3 to 5 months of age. We also measured their feeding activity three times a month for 24h. The three observations for a same month were pooled. We evaluated their relationship to humans at 80 and 150 days of age by measuring the manageability (during displacement, saliva collection and weighing) and the reaction to the presence and departure of an unfamiliar human after isolation in a test pen (1m×6m). Entire males expressed more social activities and were more aggressive than castrates only at 3 months of age. They were more attracted by the unfamiliar human but not aggressive towards him, and not more difficult to handle. They expressed a reduced feeding activity. Whatever the gonadal status, pigs from the enriched environment were observed more often playing, were less attracted by an unfamiliar human in a test pen. They were also easier to handle during weighing. Enriching the environment reduced agonistic behaviour of castrates and induced more difficulties to handle castrates during saliva collection, but had no effect on these behaviours in entire males. However, it decreased the feeding activity of entire males. In conclusion, we did not show any strong behavioural negative consequences of rearing entire males in stable groups. Our enrichment did not modulate so much the social behaviour of entire males, but decreased their feeding activity.