Wet weather followed by a sudden increase in temperature is causing a high nematodirus and roundworm risk on farms nationwide.
According to the monitoring service Parasite Watch, nematodirus has been reported on farms in the north east of England, as well as further south.
A farm in Stockton-on-Tees recently reported a nematodirus count of 350 eggs/g (epg) and a roundworm egg count of 560epg.
The threshold over which treatment is recommended is 250epg. Vet Maarten Boers, of the Livestock Partnership, West Sussex, says he is starting to see problems in lambs that are four to six weeks old.
He says: “These lambs are of an age where they are really starting to consume grass.
“Apart from Easter weekend, the temperatures have been quite cool, keeping worms at bay.
“However, now it is starting to warm up we are seeing some high worm egg counts and reports of nematodirus.”
Faecal egg counts will not always highlight nematodirus, as it is the immature larvae causing the losses.
Mr Boers recommends farmers only use a white drench for nematodirus if they can be sure there are no roundworms present.
Zoetis vet Dr Dave Armstrong says it is important farmers not only keep an eye out for nematodirus, but are also aware of which other worms may be challenging stock on-farm.
“If you have a mixed infestation, you need to be confident the treatment you are using is effective against both nematodirus and stomach worms. Traditionally, if farmers have nematodirus they will treat using a white wormer; which is fine, as long as there is not a mixed worm burden.
“If you have a mixed worm burden and you use a white wormer, which you may have resistance to, it is a dangerous situation,” he warns.
“When a wormer is only 60-90 per cent effective, you will not see any visual resistance issues in your lambs, but you also will not be maximising their growth potential.
“Also, you will be accelerating resistance build-up on your farm.”
He adds: “You need to find out what worms are on your farm – and which treatments are working and which are not – to protect the future of your business.”