New data 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 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 Lesley Stubbings said the project had shown that it is not necessary to blanket treat ewes – it is likely that around 80 per cent of pasture contamination is caused by as few as 20 per cent of ewes.

“We have to question why we worm at lambing time,’’ Ms Stubbings told farmers at a 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 between 12 and 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.’’

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 help farms save money, but the most important reason for not using anthelmintics if unnecessary is to protect flocks from resistance.