Impact of single-sex and mixed-sex group housing of boars vaccinated against GnRF or physically castrated on body lesions, feeding behaviour and weight gain

Physical castration of male piglets is common practice in many countries for the control of boar taint. A vaccine against GnRF (Improvac®) is licensed in Europe as an alternative to this painful procedure. Vaccinated pigs are known to behave like entire males up to the second vaccination, exhibiting more aggressive behaviour towards each other, which is of welfare concern. Previous studies showed that feeding behaviour is influenced by the level of competition and therefore possibly also by agonistic interactions in pig groups. The aim of this study was to evaluate if mixed-sex or single-sex housing as well as the castration method would influence skin lesions, feeding behaviour and weight gain. A total of 160 pigs were raised in four treatment groups (in four replicates): (1) single-sex physical castrates (C, n = 10 per pen), (2) single-sex vaccinates (V, n = 10), (3) physical castrates (CF, n = 5) housed with females (FC, n = 5), and (4) vaccinates (VF, n = 5) housed with females (FV, n = 5). The fattening time started at 11 wks and vaccinations were applied at 12 and 23 wks of age. Data were analyzed as repeated mixed models with Tukey HSD tests. A shorter feeding duration (FDV, P < 0.001) and lower feed intake (FIV, P = 0.009) per visit of V compared to C pigs, before the second vaccination (wk 20 of age), could be a consequence of more aggressive interactions at the feeder. This is confirmed by higher shoulder lesion scores in V pigs before effective castration (period 3, P = 0.036). This disadvantage is not apparent in VF groups, in which shoulder lesions were not higher and FIV/FDV were not lower compared to C and CF pigs. Feeding duration (FDD) and intake (FID) per day were lower for V (P < 0.001/P < 0.001), as well as for VF pigs (P = 0.005/P = 0.013) in wk 20 compared to C pigs. However, ADG did not differ between treatments before the second vaccination. Considerable changes occurred after the second vaccination, with a higher FID for V (P < 0.001) and a higher ADG for V (P < 0.001) and VF pigs (P < 0.001) than for C pigs; the other feeding parameters and lesion scores did not differ between treatments anymore. Although lesions were mostly superficial scratches and not severe wounds, it seems likely that agonistic interactions impair welfare. Our results suggest that for welfare improvement the second vaccination should be applied earlier in the fattening phase and GnRF-vaccinated males should be raised together with females to reduce agonistic interactions.