In this paper, nutritional influences on reproduction in boars, bulls and rams during prepubertal life and in the adult is reviewed. Reproductive functions in young animals appear to be more susceptible to dietary restrictions of energy and protein than in the adult and severe feed restriction may even result in permanent damage to gonadal and neural tissue. Whilst restricted feed intake in adult animals can reduce androgen secretion and semen quality, such effects are temporal as re-feeding previously underfed adult animals usually restores reproductive function. There is now considerable evidence suggesting that the influence of nutrition on reproductive processes is mediated via effects of dietary constituents on the hypothalamic-pituitary axis, although there is some indication that dietary changes may affect the testis directly. That some nutritional regimes imposed on animals can alter volume of ejaculates and androgen activity without necessarily affecting spermatogenesis, suggests that certain constituents of the diet can differentially affect the production and/or the release of LH and FSH.