15 February 2023


New data emerging from a study involving Welsh sheep flocks shows good potential to significantly reduce the number of ewes that need to be wormed around lambing time.

A study funded by the European Innovation Partnership (EIP) Wales and involving five commercial sheep farms across Wales clearly links increased worm burden in ewes before and after lambing, commonly known as the ‘spring rise’, with low body condition and nutritional stress.

Using that knowledge, gained from taking faecal egg count (FEC) samples six weeks before and six weeks after lambing, and with close attention to ewe diets with forage analysis to ensure ewes weren’t underfed, the farmers in the study were able to treat the least number possible.

Project specialist and independent sheep consultant Lesley Stubbings said the project had shown that it is not necessary to blanket treat ewes – it is likely that around 80% of pasture contamination is caused by as few as 20% of ewes.

“We have to question why we worm at lambing time,’’ Ms Stubbings told farmers attending a recent joint EIP Wales and Farming Connect event at Aberystwyth.

“There is the perception that it is because it does the ewe good. This is the bit that we must try to separate from. It is really all about reducing the number of worm eggs the ewes drop on to pasture in their dung, which then become a challenge to lambs later in the season.’’

Worming at lambing is deeply ingrained in the industry, she admitted.

“It is what farmers were brought up to do, but this project has shown that it is often not necessary, that a ewe’s immunity to worms is much more to do with the effect on them when their nutrition is under the most pressure.’’

Fit adult ewes have immunity to worms by the time they are 12-18 months old, with the exception of the barber pole worm, Ms Stubbings pointed out.

“They are still ingesting worm eggs but they have a nice relationship with them as in they will allow a few to exist and choose which to stay in their gut and which to shed.’’

That immune system works well until the ewe is under pressure – it then wanes and the ewe will produce high levels of eggs and shed them in her dung. 

A need to control the volume of worms contaminating pasture is a reason why farmers have wormed every ewe, in the mistaken belief that it is necessary.

Ms Stubbings said the data from the EIP study clearly showed that if a ewe is not under nutritional stress, she does not need to be wormed as FEC samples taken during the study show that she is not shedding large numbers of eggs.

It even applies to leaner ewes, she said. “The message has always been that you have to treat your leanest ewes, but just because a ewe is thin it might not be necessary to drench, it is the nutritional pressure point that matters.’’

For instance, on several of the farms, FECs increased when ewes were short of grass.

Monitoring body condition score (BCS) will allow farmers to identify which ewes to treat, leaving a higher proportion untreated.

“Combined with some FEC monitoring, they can also pinpoint the time to give a treatment for maximum effect,’’ said Ms Stubbings. 

The findings of the study will also help farms save money.

“There is a cost element to this. If we are trying to keep costs under control, there is no point in treating if we don’t have to,’’ Ms Stubbings advised.

But the most important reason for not using anthelmintics if unnecessary is to protect flocks from resistance.

The policy of blanket use of long-acting moxidectin 2% wormers must be revised because of the impact this policy could be having on resistance.

However, correctly using products with moxidectin as the active ingredient on ewes could reduce flock use overall, suggested Ally Ward of Zoetis, and fewer lambs are likely to need treating.

Year on year use of long-acting moxidectin in ewes around lambing is unadvisable in a flock, and simply rotating it with other wormer groups within a season is not enough, said Ms Ward.

“If ewes are treated with long-acting moxidectin, some must be left untreated – 10% is the absolute bare minimum and this project shows that in many cases the proportion that require treatment is much lower – but if it is being used to treat scab then everything should be treated.’’

It should not be used more than once in any one year, she added.

Ms Ward urged flock keepers to observe a high level of accuracy when dosing – they can do this by weighing animals, ensuring equipment is correctly calibrated and using best practice.

Monitoring FECs in the EIP study was done by Techion UK. Its general manager Eurion Thomas said the project had demonstrated a strong case for this approach.

“Monitoring FECs is more than just looking at lambs in the summer. There is an argument for using it to inform which ewes to treat and when. That changes from farm to farm and from year to year.

“If you use it to get the timing of dosing right, you are not wasting that product and not building up resistance.’’



Analysing forages is key to ensuring ewes get the correct level of nutrition.

By gathering this information, farmers can work out what contribution of the ewe diet is coming from forage, said Ms Stubbings. 

Only minimal compound feed is needed if she is getting sufficient nutrition from forage. 

If farmers do need to provide concentrates, Ms Stubbings said there was a big difference between those that have the best nutritional quality, and those that haven’t.

“Cheap compound feeds can be truly awful, therefore when selecting which to feed, always ask to be shown the best quality ones,’’ she suggested. 

Oil content should be no more than 4-5%. “Ruminants don’t need oil, therefore a level higher than 4-5% is unnecessary,’’ said Ms Stubbings.

Ash and fibre should be less than 10% and the crude protein as required by the ewe according to stage of pregnancy and forage content.

Ms Stubbings advised looking at the list of ingredients – these are listed in descending order with those present in the highest percentages at the top.

Although the list of ingredients on the label does not state inclusion rates, molasses is a good barometer for where each sit on the list as this is usually present at 5-6%.

“Anything above that will be higher than the molasses level, below that lower,’’ said Ms Stubbings.

Avoid feed with poor quality ingredients, like oat feed and oat pellets.

Ms Stubbings suggested the feed in buckets is an expensive means of providing nutrition – at current prices they work out at >7 pence/MJ compared to compound feed at 3.5-4 pence.

“Be aware of what you are paying for the convenience of buckets, there is absolutely nothing magic about buckets and blocks,’’ said Ms Stubbings.

“If they are necessary for convenience fair enough, but a lot of them work out at £1,000 or more a tonne, therefore be aware of what they are costing versus the contribution they make.’’

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