Abstract

Anthelmintic resistance in gastrointestinal nematode (GIN) parasites is an increasing challenge for lamb finishing worldwide, necessitating alternative parasite management strategies. This study investigated the impact of different forage types on GIN reinfection and liveweight gain in weaned lambs. Lambs were allocated to perennial pasture (PP), first year chicory/clover (CC1), plantain/clover (PC), Raphnobrassica (RB), or second year chicory/clover (CC2) following treatment with an effective anthelmintic (Zolvix™ Plus). Over the 70 day period post-anthelmintic treatment, compared with PP lambs, lambs grazing CC1, PC and RB maintained significantly lower faecal egg counts (FEC) and achieved high liveweight gains without further requirement for drenching. These outcomes likely reflected reduced larval migration due to crop canopy architecture, lower environmental survival of larvae in crop microclimates, and improved lamb resilience to parasitism associated with enhanced nutrition. In contrast, lambs on CC2 and PP exhibited earlier increases in FEC and relatively lower liveweight gains than first year crop lambs. Higher populations of infective L3 larvae within CC2 and PP swards, and vernalisation of CC2 chicory reducing the palatability and nutritive value of CC2 may have contributed to less favourable outcomes for these lambs. Management strategies that maintain second year chicory in a vegetative state will improve lamb performance on multi-year chicory/clover crops. Incorporating well managed first year and potentially multi-year forage crops into lamb finishing systems can reduce reliance on repeated anthelmintic treatments. When combined with other sustainable parasite management strategies, forage crops can provide farmers with an additional effective tool to mitigate the challenges posed by anthelmintic-resistant GIN populations.

Westwood, C.T., Leslie J.W.R., Butcher E.L., and Hunter S.R.

Hamilton, Volume 85, Hamilton, 61-66, 2025