The rearing period of replacement stock usually involves two grazing seasons before they calve for the first time and enter the dairy herd. Gastrointestinal nematode infection can affect growth performance in either one of these grazing seasons. However, most investigators concentrated on calves in their first grazing season, partly owing to the fact that clinical disease is rarely observed in older animals. Cows also harbour gastrointestinal nematode infection, and numerous studies were conducted to investigate the effect of anthelmintic treatments on the subsequent milk yield. The result of the latter was a long-standing controversy, some claiming a positive effect, whereas others disputed the (economic) benefit of such treatments. The present paper summarizes the effects of infection on growth performance and milk production and integrates these effects within the context of the rearing period.