Vaccination of male fattening pigs with a gonadotropin releasing factor (GnRF) vaccine is regarded as a possible solution to solve the welfare problem associated with surgical castration, which causes pain and stress even when performed under local or general anaesthesia. The objective of the present study was to compare the behaviour of male fattening pigs either surgically castrated without anaesthesia (C) or vaccinated twice with a GnRF vaccine (V). Data collection took place in a commercial German fattening unit. Each treatment comprised 8 groups of 12 pigs, housed in fattening pens with partially slatted floor and liquid feed provided three times a day. Data on postures were scored from 24-h videos recorded in every week of the fattening period (16 weeks) using scan sampling with 5 min intervals. Social behaviour was analysed in weeks 2, 4, 6, 8, 10, 12, 14, 15 and 16 by continuous behaviour recording of focus animals in four blocks of 2 h phased evenly during the day. Overall, during the whole fattening period, vaccinates (V) were more active than surgical castrates (C), indicated by a higher proportion of pigs standing (C:9.3%; V:10.74%). ‘V’ animals showed a significant decrease in standing and an increase of sitting and lying after the second vaccination of Improvac. No significant effects of treatment on the total number of agonistic interactions and on biting and fighting were found. In ‘V’ the prevalence of aggressive behaviours decreased after the second vaccination which was not found in ‘C’ during the same period. ‘V’ animals showed a higher level of mounting behaviour compared with ‘C’ animals, but on a very low level. Treatment had no effect on the prevalence of play behaviour and manipulating of pen mates. It is concluded that housing of male pigs vaccinated against GnRF in single sex groups of 12 individuals does not increase behavioural problems in the fattening period compared with surgically castrated males.

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