Farmers must be on their guard against parasites throughout the year, with warmer, wetter weather and fewer cold spellsl eading to changing worm patterns in livestock.  

Data from the Zoetis Parasite Watch Scheme, which is now in its seventh-year monitoring worm egg counts from network of farms across the country, has found worm patterns to be changing yearly.   

What the Data is Showing  

In 2021, worm egg counts were low at the start of the year due to the cool, dry spring, yet in 2020, high counts were reported in many areas as early as March.  

Last year, worm egg counts peaked from June onwards once the weather became warm and wet, continuing right through the summer months. The highest counts of the year occurred in September and November. 

Zoetis vet Ally Anderson said: "Worms and their breeding habits are intrinsically linked to the weather because part of their lifecycle is outside the animal. This is why we are seeing a changing pattern to the worm challenge.  

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"Twenty years ago, it would have been unusual to see worm egg counts peaking in November, but because our seasons are less defined now, and our autumn and winters are warmer and wetter. 

"Changes in grazing practices, what stock has been brought in and past treatment history can also influence worm burdens on farms," she added.  

Eurion Thomas from Techion, the manufacturers of Faecal egg count (FEC) testing kit FECPAK^G2, said there has been a big change to the timing of treatments due to the changing weather patterns.  

"Traditionally, farmers would treat stock based on the time of the year, with many still doing this. However, now the risk periods are not so defined, it is vital farmers treat stock based on whether they need it. This not only helps ensure the treatments are effective, but also preserves wormers, protects the immediate environment and ensures the growth from animals is maximised, which is vital for farm sustainability and also in reducing emissions from livestock." 

Deciding When to Worm Livestock  

Worming decisions should ideally be based on faecal egg counts (FEC) alongside growth rate data, the body condition score of animals, and a farm's previous parasite history. Test results should also be shared with a vet or animal health advisor, who can help interpret the results and decide on the best treatment.  

Mr Thomas added: “FEC tests should be conducted in lambs from six weeks of age when they are out at grass. If test results reveal low worm egg counts and no treatments are given, a further test should be taken two weeks later to make sure nothing is missed.  

“This is because FEC tests only detect adult parasites. It can take three weeks from ingestion for the larvae to develop into adults, lay eggs and for those eggs to be excreted back into the environment in the dung. Therefore, lambs should be regularly tested throughout the grazing season,” he said.  

Ms Anderson added: "Faecal egg count tests are money well spent as they can help reduce treatment costs meaning the most suitable wormer can be used when there is a risk, reducing the resistance pressure through unnecessary treatments." 

Parasite Alerts 

Farmers can also get alerts to the parasite risk in their area by signing up to the free Zoetis Parasite Watch Scheme at  www.parasitewatch.co.uk. Parasite Watch uses weather data alongside information from sentinel farms across the country to predict the parasite risk.