Farmers have been told to be on their guard for roundworms this season after data shows a higher than average worm egg counts, despite record-breaking temperatures.
Records from the Zoetis Parasite Watch Scheme, which monitors worm egg counts from a network of 26 farms, has found last year's counts to be the highest yet.
Average worm egg counts peaked at over 950 eggs per gram (epg) in September, with levels above 250 epg seen from the end of April until the end of recording in November.
Sheep farmer Peter Baber from Weir Park Farm, Exeter, Devon, and one of the farms involved in the scheme, said despite being severely affected by the drought last year, he had higher egg counts than anticipated.
He believes the increased challenge may have come from grazing pressures due to a lack of grass and nutritional stress.
"We did more drenching than we thought we would have to do, in such dry conditions, which we found surprising," Mr Baber said.
"Because we were so severely affected by the drought, we think sheep were grazing very tight and picking up the worms.
"Because of the nutritional pressures, it perhaps compromised their ability to mount an immune response to control the worms."
Mr Baber lambs 900 ewes, consisting of Exlana, Suffolks, SufTex and Texels. He takes faecal egg counts (FEC) from each group every two weeks and conducts post-drench FEC tests 10-14 days post-drenching to check if the product has worked.
He added: "For animal performance and from a resistance point of view, it's so important to regularly do a faecal egg count test.
"Worm burdens can be very localised and change from year to year, so you can't rely on a drenching plan based on when you have done it in the past."
Zoetis vet Ally Ward emphasises the weather's impact on worm patterns: "Last year's weather was exceptionally hot.
"Yet, we still saw consistently high worm egg counts throughout the year. The average peak came in September when the rain arrived.
"20 years ago, it would have been unusual to see worm egg counts peaking in the autumn, but because our seasons are less defined now, and our autumn and winters are warmer and wetter, that is what we have been seeing.
"Changes in grazing practices, what stock has been brought in and past treatment history can also influence worm burdens on farms," she added.
Mrs Ward said that alongside FECs, farmers should also use growth rate data, the body condition score of animals, clinical signs and a farm's previous parasite history to determine whether treatment is necessary.
"Tests should be conducted in lambs over six weeks old. If test results reveal low worm egg counts and no treatments are given, a further test should be taken two weeks later to ensure nothing is missed.
"Results should also be shared with a vet or animal health advisor, who can help interpret the results and decide on the best treatment," she added.
