Anthelmintic resistance has been reported to be common on sheep farms internationally and recent research in Ireland has shown widespread anthelmintic treatment failure on sheep farms, with 49pc of anthelmintic treatments administered to lambs considered ineffective.
However, the prevalence of anthelmintic resistance on cattle farms was unknown.
Irish beef production is pasture based, with grazing animals naturally exposed to gastrointestinal nematodes.
Infection in calves can result in ill-thrift, with subclinical infection resulting in reduced growth rate.
After their first grazing season cattle generally develop sufficient immunity to prevent clinical disease.
Control of gastrointestinal nematodes in cattle is usually achieved by the administration of broad-spectrum anthelmintics.
There are currently three classes of anthelmintic licensed for the control of gastrointestinal nematodes in cattle: benzimidazole; levamisole; and, macrocyclic lactone.
These products have been highly effective in controlling GIN infection in ruminants for over 50 years; however, in recent years there have been a number of reports of anthelmintic resistance worldwide.
A new study by Teagasc outlined in its T-Research publication determined if resistance to benzimidazole and macrocyclic lactone was present on dairy calf-to beef farms in Ireland.
Sixteen dairy calf-to-beef farms, geographically spread around the country, were recruited for the study.
These farms were required to have a minimum of 40 co-grazing first-season calves.
The herd was monitored fortnightly from the beginning of May to determine the level of gastrointestinal nematode infection by collecting fresh faecal samples from 10 calves in the herd.
Forty calves from the grazing group were weighed, faecal samples collected and the animals were treated with either a macrocyclic lactone product (ivermectin) subcutaneously at a rate of 1ml per 50kg bodyweight (n=20), or a benzimidazole product (fenbendazole) orally at a rate of 7.5ml per 100kg bodyweight.
The calves returned to grass, and 14 days post treatment faecal samples were again collected.
Results showed that resistance to macrocyclic lactone was found on all 16 farms tested, while resistance to benzimidazole was found on 12 of the 16 farms tested (Table 1).
In some cases the egg count increased after administration of the anthelmintic.
In there conclusions, the authors of the study noted that the results demonstrate that anthelmintic resistance to benzimidazole and macrocyclic lactone can be detected on Irish dairy calf-to-beef farms.
They said strategies to mitigate the risk of anthelmintic resistance need to be urgently put in place and control practices, which reduce selection pressure on nematode populations, need to be urgently implemented.
Such practices include avoiding treating too frequently, avoiding suboptimal dosing, and implementing a good biosecurity protocol for bought-in stock.
By: FarmIreland Team