20 June 1997

Dont mix them up

SHEEP producers are being warned not to contemplate mixing wormers from different categories in an attempt to overcome anthelmintic resistance.

Because of the differing formulations of benzimidazoles and levamisoles, a cocktail of drenches will lead to the benzimidazole precipitating out causing serious variance in the efficacy of the mixture during its use over a large number of sheep.

"In New Zealand, where anthelmintic resistance is now a major problem, farmers are already mixing all three types of worm drench, but this is a dangerous practice and is illegal," says Gerald Coles of Bristol University. &#42