Effect of pasture species on internal parasites of lambs

Abstract

Increasing resistance of gastro-intestinal nematode parasites to anthelmintics and consumer resistance to the possibility of residues in animal products have prompted research on the effect of pasture species on nematodes and animal performance. Lambs (either infected with high rates of gastrointestinal nematodes or maintained nematode-free) were grazed on pure swards of chicory, high- or low-endophyte ryegrass, cocksfoot, tall fescue, lucerne, lotus, white clover or plantain. Infected lambs that grazed chicory had lower faecal egg counts and adult nematode populations, and higher carcass weights, than lambs grazed on plantain or the grass species; lambs that grazed legumes generally had intermediate counts, populations and weights. When kept parasite-free, carcass weights were up to 48% greater than in the nematode infected treatments. On farmlets run over 3 years, substituting 30% of the ryegrass area with lucerne or replacing the ryegrass with a multi-species mix consisting predominantly of bromes, tall fescue, phalaris, timothy and red and white clover, had no effect on gastro-intestinal nematode larvae, lamb faecal worm egg or adult nematode numbers. It is concluded that a diet of pure chicory affects internal parasite populations but the small proportion included in the farmlet studies had no effect.