Anthelmintic resistance 'may be common' on dairy calf to beef farms
Anne Kelleher, Barbara Good and Orla Keane of Teagasc undertook research to discover the extent of anthelmintic resistance on beef farms
Irish beef production is predominantly pasture-based, with grazing calves naturally exposed to gut worms.
Gut worm infection can cause ill-thrift and good worm control is highly dependent on effective worming products.
However, a direct and unavoidable result of the continuous use of wormers is the development of drug-resistant worms.
These are worms that can survive a dose of the wormer that would normally kill them. The main gut worm species which infect cattle in Ireland are Ostertagia and Cooperia.
Ostertagia is the main genus associated with disease, while the less pathogenic Cooperia is the main contributor to faecal egg counts.
Disease may also be more common in the second half of the grazing season due to the build-up of larvae on pasture over time.
There are currently three classes of anthelmintics available for the treatment of gut worms in cattle, benzimidazoles (white drenches), levamisoles (yellow drenches) and macrocyclic lactones (clear drenches).
Anthelmintic resistance to all three classes of drugs has recently been found on Irish sheep farms; however, the extent of resistance on cattle farms was unknown.
We therefore tested for resistance to benzimidazole (fenbendazole, oral) and macrocyclic lactone (ivermectin, injectable) on 16 dairy calf to beef farms using the faecal egg count reduction test.
A fully effective anthelmintic dose reduces egg count to zero after administration. If the egg count reduction is less than 95%, then anthelmintic resistance is present. On all 16 farms, the ivermectin treatment failed to reduce the egg count by >95%.
On 12 farms, fenbendazole failed to reduce the egg count by >95%, while on the remaining four farms fenbendazole was effective.
This indicates that anthelmintic resistance may be common on Irish cattle farms.
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