Sustained wet weather has put ewes under pressure this winter, meaning loss of body condition score (BCS) will be a valuable guide when deciding which ewes to worm around lambing.
That is the message from experts at the Sustainable Control of Parasites in Sheep (SCOPS) group, which is urging farmers to move away from blanket worming of ewes and towards a more targeted approach.
Speaking on behalf of SCOPS, sheep consultant Lesley Stubbings says: “Healthy adult ewes in optimum body condition have good immunity to roundworms and will sustain this if they are well fed, even under the stress of lambing and rearing lambs.
"Ewes in poor condition will struggle and it is these sheep that will have a compromised immunity, shedding large numbers of worm eggs in their dung.
"These eggs will contaminate spring pasture and allow a build-up of larvae when young lambs begin eating grass and are exposed to roundworms for the first time.
“The recommendation used to be to treat all ewes at lambing time to counteract what we call the ‘peri-parturient rise’.
"As our understanding of nutrition and ewe immunity has improved, we now know that treating all ewes isn’t necessary and speeds up the development of anthelmintic resistance.”
By assimilating results from new research, experts at SCOPS have continued to hone their advice to farmers around lambing time.
Having previously said to leave a proportion of the flock untreated, they now recommend targeting treatment specifically to ewes under nutritional stress – which can be measured as a loss of body conditional score.
Mrs Stubbings says the peri-parturient rise remains a threat to lambs and so wormers are an important tool to reduce pasture contamination and the subsequent challenge to lambs.
“But it’s really important to target which ewes you treat, rather than inadvertently creating a different problem further down the line by blanket treating everything. In many cases only a small proportion of ewes need to be wormed."
Most farms have experienced a very wet winter that will have taken its toll on many ewes, with some farms also unable to relocate ewes to better pasture due to bluetongue movement restrictions.
"Whatever the reason why, it is the ewes who’ve lost body condition that need to be targeted," Mrs Stubbings goes on to say.
"If you just treat those females, which are the ones more likely to produce a high number of worm eggs in their dung, you can reduce the total amount of anthelmintic used this spring compared to blanket treating, without impacting production.
“If you’ve followed this approach before, it wouldn’t be surprising to find yourself treating a few more ewes this year than in previous seasons, given the pressure some ewes have been under. “
