A new report published in London by the agriculture and science consultancy Farm Animal Initiative, “Entire Male Pig Production: Welfare Management Issues,” highlights a range of possible solutions to tackle welfare issues caused by entire males in commercial units.

These include selection of genetic lines with reduced aggressive tendencies, modification of housing environment to reduce the level of social contact, provision of manipulable materials which allow natural rooting behavior and temporary reduction of testosterone in male pigs through an Improvac welfare management program. It also outlines the problems caused by these animals in commercial units, including aggression and injury caused by sexual behavior, and considers some of the options for reducing their prevalence. 

The report points out that while entire male pigs are capable of higher and leaner growth rates compared with females and castrates, when reared under commercial conditions they rarely reach this potential due to increased aggressive, sexual and social behavior and reduced feeding behavior. “Modern commercial pig systems put pigs in challenging social situations and can result in a range of abnormal, or normal but unwanted behaviors, leading to welfare concerns," said the report. "Rearing entire male pigs in these systems increases the challenges in terms of levels of aggressive, sexual and social behaviors for all pigs in the pens."

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Injuries acquired through aggression and mounting include skin lesions, bruising and leg problems. Other problems include stress and pregnancies and subsequent slaughter of pregnant gilts. In general, aggressive behaviors are increased in entire male pigs during and after puberty, and are also increased during the mixing and moving of these animals. Studies have indicated that increased aggression is stimulated by testicular steroid hormones, and that these behaviors stimulate an increase in plasma testosterone, forming a positive feedback level between hormone levels and aggressive and sexual behavior.

“Rearing entire male pigs can give producers an advantage in terms of a potential growth rate advantage, and obliterates the need for painful castration procedures for the pigs," said report author Ruth Clements said. "However, rearing entire male pigs can present its own challenges which can leave producers unable to capitalize on any growth rate potential, and leave pigs exposed to other welfare problems resulting from aggressive and sexual behaviors.”

The report was commissioned by Pfizer.