Sheep farmers are putting their ewes at risk when worming them at lambing time and need to be careful of the long term impact of this.

Farmers are being reminded of the importance of only worming their ewes when necessary at lambing to minimise the threat from anthelmintic resistance. Traditionally, farmers have routinely wormed ewes around lambing as ewes are more prone to shedding eggs due to their lowered immune status.

However, reports of an overuse of wormers at lambing and an increase in the prevalence of moxidectin resistance in the UK has raised industry calls for farmers to be more selective when it comes to worming.

Speaking on behalf of Sustainable Control of Parasites in Sheep (SCOPS), Lesley Stubbings said: “The priority must be to preserve moxidectin 2% both as an anthelmintic for worms and a treatment for sheep scab. In order to do this, the sheep industry must prescribe moxidectin responsibly, by applying the SCOPS principles.

“This means sheep farmers working with whoever prescribes their anthelmintic, should ensure the treatment is always given at the right dose rate, administered correctly and some worms remain unexposed to the treatment by leaving some ewes untreated,” said Lesley.

Treating at lambing

The risk period when ewes immunity is lowered is from about two weeks before lambing to around six weeks post lambing. This can lead to increased egg production by female roundworms – a period termed the Spring Rise.

Moxidectin 2% is the only product proven to suppress the Spring Rise1,2 and is the only wormer that persists long enough to suppress egg output from the ewes, according to Zoetis vet Ally Anderson.

“Cydectin Long Acting Injection, which is a 2% moxidectin product has a worm persistency period of up to 111 days. Its long persistency means it can help reduce the risk of pasture contamination and therefore reduce the need to treat the lambs, saving time, money and reducing the number of wormer dosings on the farm,” said Lesley.

Farmers wishing to treat their ewes at lambing should

1. Only treat ewes when necessary and leaving the fittest ewes untreated. Ideally, at least one in 10 ewes in each grazing group should be left untreated. For example, although fit or single bearing ewes should be left untreated, if they are grazing separately to twin-bearing ewes, one in 10 ewes in that group should also be left untreated.

2. Only use moxidectin 2% once in any flock in one year and only when it is needed. Moxidectin 2% is a long-acting persistent wormer and is the only wormer that persists long enough to suppress egg output from the ewes, thus helping reduce the risk of pasture contamination and the need to treat lambs.

If it has been used to suppress the spring rise it should not be used again to treat scab within the same season. Plunge dipping should be considered for scab treatment where moxidectin 2% has been used at lambing. If it is not possible to plunge dip then an ML injection is the only option and other steps should be taken to reduce the impact on resistance development.

3. Year on year use of moxidectin in ewes around lambing is unadvisable in any flock. Simply rotating with other wormer groups within a season is not enough

4. Don’t forget Nematodirus. This is not controlled by treating the adult ewes around lambing.

5. Always ensure the right animal is treated with the right dose and in the right way.