8 August 1997

Resistance to wormers imminent?

RESISTANCE to all sheep wormers could occur within three years in the UK unless producers adopt more stringent control strategies.

Results of a survey into anthelmintic use and resistance in UK sheep – published in last weeks Veterinary Record – showed that only 17% of sheep producers treated all brought-in sheep with a suitable wormer.

The survey was conducted by Bristol University-based parasitologist Gerald Coles, who says that in addition, only 7% of producers polled, tested purchased sheep for resistance.

Dr Coles believes there should be a compulsory system for declaring the health status of sheep at sales because until there is, producers do not know which wormers have been used by the seller.

Treating brought-in sheep

If this is the case he suggests treating brought-in sheep with a group three-type wormer. Resistance to these wormers has yet to be identified in sheep and so the approach is likely to be the most effective.

"Until this strategy has been adopted we can assume that group one – benzimidazole – and group two – levamisole – resistant worms are being disseminated through the UK flock," says Dr Coles.

His survey also showed that only 15% of producers used a vet to help plan an effective control strategy. He warns producers that they must realise dosing is only part of a control strategy which is influenced by weather, grazing management and the threat of resistance.

"If a more responsible attitude to worming is not adopted wormer resistance to all groups will occur in the next two to three years."