The secretion of sex steroid hormones by the gonads of male and female farm animals improves performance, food conversion efficiency and meat content of carcass, but can adversely affect behaviour and meat quality. In particular, androgens produced by males induce aggressive and sexual behaviour, which make it difficult to manage pubertal bulls during the finishing stage. Castration, depending on age of male, can cause temporary stress but it results in decreased productivity of 7-10%, reduced feed conversion efficiency of 3 to 5%, reduced carcass weight and increased fat deposition in the carcass. Pubertal boars and bulls also produce meat that is less desirable from the consumer’s perspective due to boar taint and toughness of bull beef. The expression of recurrent periods of transient oestrous behaviour in beef heifers following puberty and cull cows can cause managerial problems and result in up to 15% of beef heifers in US feedlots being pregnant. This causes loss of productivity and increased stress if pregnant animals remain in the feedlot. Thus, the suppression of recurrent oestrous periods in beef heifers is desirable provided performance is not compromised. Ovariectomy is difficult to perform, causes stress and reduces performance by 3-5%, while the use of progestogens to suppress oestrus is prohibited by legislation in the EU. Thus, alternative methods that are conducive to good performance, meat quality and welfare have been sought. The most promising alternative approach developed over 20 years ago is to immunocastrate animals by immunizing them against gonadotrophin releasing hormone (GnRH), thereby suppressing LH and FSH secretion. This causes temporary anoestrus in females or reduced androgen secretion, testes size and aggression in males.