Preparing a dosing plan on sheep farms is underway for some farmers across the country who are currently lambing.
According to Teagasc advisor Glen Corbett, grazing sheep are continually exposed to gastrointestinal nematodes (stomach worms).
In the case of lambs, he said heavy infection can result in a depression in appetite and increased protein loss from the gut, which results in ill-thrift and in severe cases even death.
Two major types of stomach worms infect lambs, nematodirus and strongyles.
Nematodirus is a lamb crop to lamb crop infection. Corbett explained this is due to the fact that eggs passed by lambs one year hatch the following spring and are available to infect the next year’s crop of lambs.
Therefore, the Teagasc advisor said nematodirus can be a major cause of parasitic gastroenteritis in young spring lambs.
Corbett said the Department of Agriculture, Food and the Marine (DAFM), in conjunction with Met Éireann, predict when nematodirus eggs will hatch and every year produce a forecast predicting the peak hatch and advise when farmers should treat to prevent disease due to this parasite.
Assuming exposure, lambs develop immunity to nematodirus relatively quickly, usually from three-months-of-age.
Watch out for this warning, it might come before the end of March this year.
Any lambs on the ground that are over two-to-three-weeks-old will need a white dose at that stage.
Later in the season, i.e. from June onwards, other stronger worms predominate. Immunity to these worms is slower to develop, although sheep generally have good immunity from one-year-of-age.
However, older sheep can be susceptible to these worms if immunocompromised or under stress, the Teagasc advisor added.
Control and treatment
Good stomach worm control is highly dependent on the availability of effective wormers when dosing sheep.
Despite the large number of products on the market which fall into one of these classes.
- Benzimidazole (white wormer);
- Levamisole (yellow wormer);
- Macrocyclic lactones (clear wormer).
Knowing which anthelmintics (doses) are effective on the farm is a pre-requisite to ensuring that an appropriate anthelmintic is used.
The best anthelmintic is one that works on your farm. Contact your vet or advisor for full details on how to check anthelmintic efficacy.
Anthelmintic resistance refers to the ability of worms to survive a dose that should kill them.
Wormers from different classes have different modes of action.
However, within the same class all products share the same mode of action and therefore when resistance develops to one product within a class generally other products in the same class are also ineffective.
Anthelmintic resistance in Ireland
Below are four actions provided by Corbett to slow the development of anthelmintic resistance:
1. Dosing sheep:
Do not dose mature ewes for stomach worms unless there is a demonstrated need. Thin, immunocompromised or otherwise sick ewes may benefit from treatment.
2. Use only white wormers to control nematodirus:
To-date, anthelmintic resistance has not been recorded in nematodirus in the Republic of Ireland.
Resistance to white wormers is common in the strongyle worms that predominate later in the season; therefore, this wormer will not be effective on many farms later in the season.
Using white wormers to control nematodirus will reduce use of the other wormers and represents appropriate use of an anthelmintic to control infection.
3. Implement a good biosecurity protocol for bought in sheep:
Animal movement is a major way in which anthelmintic resistance can spread.
In order to prevent bringing resistant worms into the farm, incoming sheep should be quarantined and treated.
Sheep should then be housed for 48 hours to allow any eggs that might already be in the gastrointestinal tract to pass out.
They should then be turned out to pasture recently grazed by sheep which will contain the worm population found on that farm and dilute any resistant worms surviving in the treated sheep.
4. Use faecal egg counts:
Faecal egg counts determine the number of worm eggs in a dung sample and provide a useful indicator of the level of infection in a flock.
Faecal egg counts can be used from weaning onwards to determine when treatment is required.
A composite faecal sample, from 10-15 lambs in a group, can be submitted to a laboratory for analysis.
A faecal egg count of 600 eggs/g or above may indicate the need to treat. Monitoring faecal egg count will ensure that animals are only treated when necessary and that a susceptible population of worms in refugia is maintained.
Faecal egg counts should also be used to determine which anthelmintics are effective on the farm.