Lowering anthelmintic reliance

More than 80% of flocks in Wales are carrying worms that exhibit some degree of anthelmintic resistance, according to latest survey results.

The Wales Worm Watch project, initially set out to determine whether claims of a growing resistance problem were justified, showed resistant nematodes were found in 83% of samples collected on 125 farms.

Worms resistant to benzamidazole (BZ) anthelmintics were present in 49% of samples, while 30% contain worms resistant to both BZ and levamisole (LM) anthelmintic groups.

Faecal samples were collected from a statistically significant cross section of farms throughout Wales.

Small and large, hill and lowland, pedigree and commercial flocks were included to ensure the units selected were representative of the Welsh national flock.

Larval development assays, in which nematode worm eggs found in the faeces were incubated with different groups of anthelmintics, were conducted by the Vet Lab Agency’s parasitology department.

To assess the extent of resistance VLA technicians at Aberystwyth and Weybridge counted the number of larvae that developed in the presence of the different concentrations of anthelmintics.

Only 5% of samples contained worms that were only resistant to LM products.

But, results surprised members of the team conducting the survey, who expected incidence of anthelmintic resistance to be closer to the outcome of a University of Wales pilot study in 2004, which indicated BZ resistance on 70% of farms.

The level of anthelmintic resistant nematodes in Wales clearly demonstrates incidence is not only widespread but is increasing, says Prys Morgan, HCC’s industry development manager.

Of equal concern are the results of a questionnaire on drenching practices, which was conducted at the same time.

It indicated that farmers were not heeding advice about doing the job effectively.

More than 50% of respondents were continuing to use the same drench groups despite recommendations to change group annually.

“Also, more than 40% of flockmasters only estimated the weight of animals before drenching, and 41% did not carry out a quarantine drench when new sheep were brought onto their farms.”

Barbara McLean, who led the ADAS team, says this is a serious national problem that needs to be acknowledged and tackled.

We must reduce our reliance on anthelmintics and when they are used they must be used correctly.”

She advised calibrating drenching guns regularly and allowing enough time to ensure the right amount of drench is administered.

“It is important all farmers store drenches correctly, and use the correct dose rate based on weight of the heaviest sheep in the group,” adds Mr Morgan.

Farmers should monitor faecal egg counts to ensure flocks are treated only when necessary and operate strict quarantine procedures to avoid buying in resistant worms.

“We are encouraging farmers to consult their vet to discuss parasite management.

Where resistance has been detected it may be at a level where clinical signs are not marked, but continued use of that type of anthelmintic could allow resistant worms to increase rapidly.”

Other classes of anthelmintics should be used, but farmers should check that they are working by carrying out worm counts before and after treatment, he advises.

“Sheep farmers could do a lot to reduce dependence on drugs.

Pasture management incorporating the use of low risk grazing like silage aftermaths, alternate grazing with cattle, cutting stocking rates and earlier lambing could help.

“Breeders should also be encouraged to consider breeding from animals which are known to be less susceptible to parasites,” he added.

Field work and results analysis were done by ADAS Pwllpeiran.

The study was managed by Hybu Cig Cymru (Meat Promotion Wales) and funded through the Welsh Assembly Government’s Farming Connect initiative.