As anthelmintic resistance in gastrointestinal nematode (GIN) populations poses a great threat to small ruminant health and productivity worldwide, researchers look towards alternative methods to control GIN. The present study objective is to evaluate the efficacy of grazing birdsfoot trefoil (BFT), a forage with high levels of condensed tannins, as a biological means of controlling Haemonchus contortus infection in lambs with natural GIN infection. Body weight, fecal egg count (FEC), and packed cell volume (PCV) measurements were compared between lambs grazing BFT and grass. It was found that BFT lambs had mitigated infection severity with lower FEC and higher PCV compared to grass lambs. However, this effect was lost when lambs stopped grazing BFT, at which point their FEC increased dramatically and PCV fell. There was no growth differences between the treatment groups. Grazing BFT may be beneficial in an integrated GIN management plan as it increased resilience to infection.