Abstract
Male piglets are castrated primarily to avoid the unpleasant boar taint in meat, and additionally for the predisposition of castrates to accumulate fat and for their lower risk of developing unwanted behaviours. There are two main strategies available for withdrawing from surgical castration: one is immunocastration and the other is to raise entire male pigs or boars. Additionally, raising intact boars is more profitable because of the production of carcasses with lean meat and better feed conversion. Boars (compared to castrates) exhibit more aggressive, sexual, damaging social behaviour and reduced feeding behaviour with a lower prevalence of sickness behaviour as a result of good health and low susceptibility to chronic inflammation. In this review, the behaviours specific for boars as a result of sexual maturity are reviewed, with an overview of differences in the behaviour of surgically castrated barrows, immunocastrates and boars reared in group-housed systems. The raising of boars allows for good welfare of these animals in early life, but later, on reaching sexual maturity, the welfare of boars can be diminished because of their propensity to aggression and more mounting behaviour than castrates. Innovations in the breeding and management of boars are needed to improve their performance and to reduce welfare implications of these animals raised in social groups, and in particular to minimize deviant behaviours towards pen mates.
Highlights
SEXUAL MATURITY AS RISK FOR DEVELOPMENT OF DEVIANT BEHAVIOURS IN PIG PRODUCTION SYSTEMS WITH ENTIRE MALES
Farmers have traditionally castrated their male piglets surgically to avoid the boar taint of pork and to reduce male-specific behaviour, and this procedure is still common in most countries
The concentrations of serum testosterone and oestrogen are raised in male piglets during the first three weeks after birth, leading to increased prepubertal mounting activity and higher numbers of social interactions compared to gilts or castrated boars (Berry, 1984)
Summary
Immunocastration is a provisional form of castration. Immunocastration can cause complications that are similar to those of any other injection of pigs in a production system. Aggressive behaviours t The lack of environmental enrichment such as manipulable materials is common in s confining rearing systems, which are associated with high competition for resources such as food and water This competition between pen-mates contributes to the ir animals carrying out normal behaviours at a high frequency and to the extent that they become problematic, resulting in increased social and body contact with other pigs. The concentrations of serum testosterone and oestrogen are raised in male piglets during the first three weeks after birth, leading to increased prepubertal mounting activity and higher numbers of social interactions compared to gilts or castrated boars (Berry, 1984) The manifestations of these behaviours reach peaks at around two months of age, and in prepubertal pigs they decline to a low frequency (Ford, 1990). The masculinisation of sexual behaviours in boars is strongly dependent on the increased secretion of testicular steroid hormones that begins from three months of age continuing through six months of age (Ford, 1990), which correlates with escalating aggressive and sexual behaviours in entire males (Cronin, 2003)
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