Parasite Resistance an Emerging Problem for Sheep Producers
28 February 2005
Gastro-intestinal parasites (roundworms) are a ‘fact of life’ for sheep but good flock management practices including appropriate use of anthelmintics can control their negative effects on animal performance according to Teagasc Research Scientist Dr. Barbara Good speaking at the Annual Sheep Conference organized by the Irish Grassland Association recently.
Because parasites are not all equally susceptible to the effects of an anthelmintic the proportion of resistant worms on a farm is increased if anthelmintics are used inappropriately, for example over-reliance on anthelmintic treatment, over time said Dr. Good. When this happens the anthelmintic treatment will be ineffective. Switching to an alternative class of drug may solve the problem but without the adoption of good practice the same problem will develop in relation to the new drug.
The Teagasc Researcher told the meeting that there are only three different classes of anthelmintic available for use and that inappropriate use will lead eventually to unmanageable parasite problems on sheep farms. Results from an on-going study at Teagasc Sheep Research Centre, Athenry, in collaboration with Veterinary Faculty UCD, reveal an emerging problem with anthelmintic resistance on many sheep farms in Ireland.
An evaluation of samples, carried out by Teagasc, obtained during 2004 from lowland flocks throughout the country shows a significantly increased incidence of roundworms resistant to benzimadazoles (white drench) on about 70% of farms while over 20% of farms had increased resistance to levamisole (clear drench). These findings highlight the need for increased awareness of the principles of sustainable use of anthelmintics as part of an overall strategy for parasite control. Other Teagasc research has identified a number of ways which can enable a reduction in the frequency of anthelmintic treatment, such as using sheep breeds that have a high level of resistance to roundworm parasites (e.g. Texel and Belclare) and by checking the parasite burden of lambs before treatment to establish whether treatment is really required.
In the light of the evidence on anthelmintic resistance Teagasc recommend that farmers have an annual check done to determine the resistance status of the parasites on their farm and highlight the need to adopt control practices that minimize the risk of selecting for increased parasite resistance to anthelmintics.
