Recent rainfall after an exceptionally dry summer for most of the country could mean sheep farmers face a double threat of worm and liver fluke challenges at the same time this winter.

“Parts of the country where it has been very dry this summer will see the ‘worm season’ start a few weeks after the rain comes,” says Elanco ruminant technical consultant, Matt Colston.

“This activity will continue until we have a spell of frosty weather – but if it remains cool and damp larvae can survive on pasture for months.”

This sudden start to the worm season after a long dry spell can give lambs a significant larval challenge, sometimes causing disease before any adult worms are present.

“Worm egg counts could lag behind the true worm burden under these circumstances,” he says.

However, with that exception, faecal egg counts are still one of the best aids in deciding if and when to treat for worms in the autumn and winter months.

“For many farms this will be the right point in the grazing/worm season to be using one of the newer group 4 or 5 wormers as a break dose for lambs.”

In areas where it has been hot and dry all summer, the likelihood is that any liver fluke challenge will come later in the year than normal, but this does not rule out a potential overlap with a later worm season, he adds.

“Even in dry areas, some farms will have small, localised areas that have remained damp enough to maintain a snail habitat and the liver fluke life cycle, so getting a clearer picture of what is happening on farm can really help inform treatment timings," says Mr Colston.

With changeable weather patterns and unpredictable parasite seasons, sticking to routine treatment dates for liver fluke is unlikely to give the best level of control, he advises.

However, monitoring fluke challenge is not as straightforward as keeping an eye on worm burdens and needs the right tests to be used in the right animals at the right time. This should be discussed with your vet or flock health adviser.

Post-mortem examination of any dead stock, even when it’s obvious why they died, is a good first step, and can help determine if liver fluke and/or worms are present but ‘under the radar’.

It is also worth noting the clinical signs of liver fluke are very similar to those of Haemonchus contortus, also known as Barber’s pole worm.

“If you suspect fluke it’s worth testing to see if it could be Haemonchus,” Mr Colston concludes.