Research - Stories

Parasite ecology

31 Oct 2007   Managing drug resistance

Managing drug resistance

The Hopkirk's Parasite Ecology team is searching for ways to stop escalating drench resistance in livestock.

The team, led by Dr Dave Leathwick, has carried out a national survey on worm management practices and the prevalence of drench resistance on New Zealand sheep and beef farms - with alarming results. This research showed the spread of resistance is 20 years ahead of levels predicted three years ago.

"Treatment efficacy of about 50% - 80% can result in significantly lower growth rates and a subsequent loss of profitability as animals take longer to reach target weight," says team member Dr Tania Waghorn.

"In the worst case scenario, total drench failure can lead to clinical parasitism and death of the animals."

Dave says farmers must act now to preserve the efficacy of existing products because no single drench family remains effective against all nematode parasites and no new drenches are likely in the near future.

"We try to recreate real farming systems and have set up our own farmlets which mimic larger-scale enterprises. To help us understand current practices and make the trials as relevant to as many farms as possible, we work closely with a mentor group, made up of farmers, vets and consultants who not only provide valuable input but help transfer our research outputs to a wider audience. On our farmlets we compare the impact of different management practices on both worm control and drench resistance."

Collected faeces are used in various ways, from counting the number of eggs which gives an indication of how many parasites are present in the animal, to allowing the eggs to hatch and grow to larvae. A major aspect of the research is finding a balance between effective worm control and minimising selection for resistance.

"Worm management is a trade-off between controlling parasite levels versus anthelmintic sustainability," says Dave.

Selective drenching is also being evaluated by the team, along with its trying to understand the ecology of the parasites.

"If you look at what the parasites are doing on the ground and how they develop during the year, you can use the information to help develop effective worm control strategies," says Tania.

For more information: dave.leathwick@agresearch.co.nz.