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Parasite Matters Summer 2021

The weather over the last three months has been variable to say the least. After a cold January and February, March came in warmer and drier than average for most areas (picture1). April on the other hand, was very dry for the whole country, and much colder (picture 2), with the “frost days” (picture 3) emphasising just how cold it was across all areas.

How will this affect the parasites? For sheep farms the impact on Nematodirus and blowfly strike will be of most concern, while for cattle, the challenge from GI worms and flies may change.


  • Blowfly activity will also have been affected by the “stop-go” weather. Although the NADIS risk forecast is still at “low” across the country, south facing corners of the farm may well have had high enough temperatures for strike to occur, with active strike already reported as far north as Scotland as shown on the blowfly tracker. Again, strike risk will increase rapidly as the weather warms up, so application of a blowfly prevention product before the flies land is the best way to reduce that risk.
Nematodirus forecast

  • Nematodirus activity started for some in the warmth of March, then slowed to a standstill again in the cold of April. May has been warmer and wetter so the risk is now changing daily (see the SCOPS nematodirus forecast. The “stop-go” weather will mean a trickle hatch in some areas, allowing lambs to develop immunity without obvious disease, while in other areas the hatch will be delayed and be more likely to coincide with later born lambs eating more grass. So keep an eye on your lambs and the forecast.
Cattle grazing


  • For cattle farms, youngstock at grass that have not already been treated for worms should be monitored closely (using worm egg counts or Daily Live Weight Gain), as depending on last year’s grazing management, the worm burden on pasture could increase rapidly in the current warmer, wetter conditions.
  • Like blowflies, the biting and nuisance flies that bother cattle will start to appear shortly and rapidly increase in number as the weather warms. Also like blowfly, treating when the fly numbers are low will help to reduce fly numbers overall, giving better control for the season. In the dairy situation where animals are often in and around buildings, environmental control measures (including controlling fly eggs/larvae in the environment) will make a big difference. See here for more information.
liver fluke

  • Liver fluke disease is seen as an autumn/winter problem, but as we mentioned last time, a targeted adulticide treatment in the late spring/early summer for any cattle or sheep that might still have the odd adult fluke inside, will make a big difference to the level of fluke challenge for the coming autumn. The weather at this time of year (May/June) also has a huge impact on the fluke risk for the autumn and winter – watch for an update in the next bulletin.

Parasite Matters Archive

Parasite Matters Spring 2021 (published March 2021)
Parasite Matters Autumn 2020 (published September 2020)
Parasite Matters Summer 2020 (published June 2020)

CLiK™ EXTRA 65 mg/ml Pour-On Suspension for sheep contains dicyclanil and is indicated for the prevention of blowfly strike on sheep caused by Lucilia sericata or Wohlfahrtia magnifica. Rycoben™ SC 2.5% w/v Oral Suspension for Sheep contains cobalt sulphate, ricobendazole and sodium selenate, and is indicated for the control of broad spectrum roundworms, tapeworms, lungworms and fluke in sheep. Flypor™ 4% w/v pour-on solution contains 4% w/v permethrin (cis:trans 80:20). Legal category: POM-VPS. Advice should be sought from the medicine prescriber prior to use. Use medicines responsibly ( Neporex™ is an insecticide for professional use against nuisance flies and biting flies in animal housing and landfill sites including waste management sites. It contains cyromazine, an insect growth regulator. It disrupts all stages of insect development by interfering with the production of chitin. Legal category: Biocide. Use biocides safely. Always read the label and product information before use. Weather maps courtesy of the Met Office. For further information call Elanco Animal Health on +44 (0)1256 353131, or write to Elanco UK AH Limited, Form 2, Bartley Way, Bartley Wood Business Park, Hook, RG27 9XA. CLiK™ Extra, Rycoben™, Flypor™, Neporex™, Elanco and the diagonal bar logo are trademarks of Elanco or its affiliates. © 2021 Elanco or its affiliates. PM-UK-21-0542