Immunocastration with Improvac™ reduces aggressive and sexual behaviours in male pigs

Abstract

Surgical castration of male pigs is a common practice to reduce the risk of boar taint, an accumulation of pheromones in the muscles of pigs giving an undesirable odour to the pork of entire boars. Castration is not widely practiced in the UK for welfare reasons and indeed, assurance schemes will not allow castrated animals into their markets. Immunocastration maintains entire male pigs in a pre-pubescent state and as such prevents boar taint in the meat. The aim of this study was to investigate the effect of early vaccination with a gonadotrophin releasing factor (GnRF) vaccine Improvac™ (Pfizer Ltd) on aggressive and sexual behaviour of group housed male pigs. Pigs were housed in 8 groups each containing 9–10 pigs per group. Male pigs were assigned to two groups: a control group administered 2 doses of a placebo (n=38) and a vaccinated group administered 2 doses of Improvac™ (n=38). Behavioural observations began one week after the second dose when the pigs were 16 weeks old. Pigs were video recorded for 30min once a week for 10 weeks.Video recordings were reviewed and the frequency of behaviours associated with sex and aggression were recorded on a pen basis. The activity of pigs was also recorded every 5min during the 30min observation period to determine any differences between vaccinated and control groups. A generalised linear mixed model was used for data analysis. The results of the model showed a significant difference between vaccinated and control groups for knocking (P<0.05), fighting (P<0.05) and mounting (P<0.01) behaviours. Vaccination had no significant effect on the activity of pigs during the recording period. In conclusion early immunocastration of pigs significantly reduces the occurrence of unwanted aggressive and sexual behaviours compared with unvaccinated control male pigs.