16 August 2002

Review sheep wormer policy

MOVING stock to clean pasture after worming must be stopped if producers are to retain a range anthelmintics for use in sheep, according to Gerald Coles of Bristol Vet School.

"The use of clean pasture should be encouraged, but not for animals recently treated with anthelmintic. Present use of anthelmintics on many sheep farms, involving frequent treatments or dose and move strategies is simply not sustainable," says Dr Coles in a report in Vet Record.

Dr Coles suggests moving treated animals to clean pasture will encourage resistance to anthel- mintics as the only contamination reaching the clean pasture will come from worms which have survived treatment.

He also believes basing treatment policies on faecal egg counts can be unreliable because of the widely different rates of egg laying by different species of worms, and the poor relationship between egg counts and worm burdens in animals infected with nematodirus species.

"An adequate indicator of the need to treat may be scouring. However, the idea of putting sheep in a race and treating them all will have to become a thing of the past," he says.

Future treatments will ideally be based on vaccines, but he says practical vaccines are some way off and need research funding. Breeding for resistance to nematodes may help in the meantime, but it is a long-term strategy, which increases susceptibility to other infections. &#42