Pregnant ewes are a major source of worms on pasture during the grazing season, which is why farmers have traditionally wormed their pregnant stock.
However, with anthelmintic resistance on the rise and blanket treatment of ewes a risk factor in the speed that resistance develops, it is important sheep farmers have a strategy in place that manages worms and also protects their wormers for the future.
Lesley Stubbings, from the Sustainable Control of Parasites in Sheep (SCOPS) group, offers some advice on how to control worms around lambing.
Is there the need to worm around lambing?
Worming ewes around lambing is common practice in UK flocks, but whole-flock treatments are costly, time consuming and add to the speed with which worms develop resistance to wormers.
The rationale behind treating ewes is that it reduces the number of worm eggs a ewe puts onto pasture when its immune system relaxes around lambing – a term known as the ’spring rise’.
Along with larvae which have overwintered, this will be the source of the worms that will challenge lambs later in the season. If farmers can differentiate between the ewes that put out the most eggs from those that shed the least, treatment can be selective.
How do you select which ewes to worm around lambing?
The ewes which produce most eggs are the priority for worming around lambing and these tend to be the ones under the most pressure in late pregnancy. This includes ewes under nutritional stress, for example, in lower body condition, younger ewes and triplet-bearing ewes.
Faecal egg counts taken around lambing can also help target which ewes to worm. Producers who have been monitoring faecal egg counts (FECs) are finding a much higher proportion can be left untreated if ewes are fit and healthy, without any detriment to performance.
How many ewes should be left un-wormed?
It is essential to leave at least 10 per cent, preferably more of the ewes untreated and these need to be spread between different grazing mobs. For example, it is not enough to simply leave singles untreated as they may be grazed in separate fields to twins or triplets. Use body condition as a guide with the fittest ewes left untreated.
What product should I worm my ewes with?
The product(s) you use should be specific to your farm and you should work with your animal health provider on a worm control strategy. It should not be the same product year on year.
Farmers may wish to use a persistent product, such as moxidectin 2 per cent long acting which provides cover for up to 111 days and is the only product available which is able to suppress the spring rise. This can help reduce the risk of pasture contamination and in conjunction with FEC monitoring can reduce the number of treatments required for lambs, saving time and money.
However, when farmers opt to use a persistent product, they should use it with care (see joint SCOPs and Zoetis Do’s and Don’ts bit.ly/37ynBPg) and must not use it year on year or within the same season. For example, if you have used the product in the ewes at lambing, you should use a different product to control scab.
The priority must be to preserve moxidectin both as an anthelmintic for worms and a treatment for sheep scab.
Wormers should not be relied on as the sole means of controlling worms on your farm. It is important they are part of a plan. A good control plan includes: