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NADIS Parasite Forecast - September

Use of meteorological data to predict the prevalence of parasitic diseases

Capture 2

Temperatures for July were above average across the UK, mainly due to warm days with many days having maximum temperatures above 25 °C, especially in the south-east. However, night-time temperatures were closer to average. There was plenty of warm, dry, sunny weather, but with the warmth leading to thunderstorms and localised downpours at times; the heaviest rain was generally across the south-east and East Anglia. (


September Parasite Forecast/Update

The most recent version of this monthly parasite forecast may be accessed at

Quarantine of purchased stock

September is the month for sales of breeding sheep.  Purchased sheep pose many potential disease risks irrespective of sale price. Quarantine treatments of all purchased stock are essential. Such treatments, and vaccination strategies, must be discussed with your veterinary practice preferably ahead of purchase but certainly before the sheep have been mixed with the home flock.

Quarantine treatments of purchased stock

  • Quarantine arrangements are essential to reduce the risk of introducing anthelmintic-resistant worms with purchased sheep.
  • Current best practice involves sequential full dose treatments with monepantel (Zolvix) and moxidectin upon arrival on farm.
  • Confine for 24-48 hours, then turnout onto pasture recently grazed by sheep.
  • Maintain purchased stock in separate groups and monitor closely for disease for at least 30 days before mixing with home flock.

Fig 2 quarantine

Despite their appearance and absence of diarrhoea, quarantine treatments are essential for replacement rams to reduce the risk of introducing anthelmintic-resistant worms.


  • Clinical PGE is likely to become a problem on contaminated grazing in many areas as larval challenge increases.
  • Monitor lamb FWECs or liveweight gain to determine anthelmintic treatments.

Fig 3 PGE

Parasitic gastro-enteritis affecting fattening lambs is more common following wet weather.

Anthelmintic treatments pre-tupping

  • In general terms, anthelmintic treatment should be targeted at leaner ewes, gimmers, or those sheep with dags.
  • Anthelmintic treatment of all breeding females pre-tupping is rarely necessary.
  • Dosing all ewes pre-tupping may select for anthelmintic resistant strains and is discouraged in the SCOPS guidelines.
  • Faecal egg counts will indicate whether ewe anthelmintic treatment is necessary.
  • Rams are often neglected at this time and a faecal worm egg count will decide whether a pre-tupping anthelmintic treatment is necessary. However, FECs in individual animals do not necessarily give an indication of parasite burdens or their impact.

Fig 4 excellent body condition

Most ewes are in excellent body condition before breeding and do not need anthelmintic treatment.

Fig 5 dags

Anthelmintic treatment should be targeted at leaner ewes, gimmers, or those with dags. Investigate cause if a high percentage of sheep are in poor condition.


Conditions over the first half of the summer (May to July) have been generally dry, and the low rainfall in most areas has contributed to a provisional early forecast of 'low to normal liver fluke disease risk'.  However if the weather changes and favourable wet conditions prevail throughout August and September, then there is still the risk of a high prevalence of liver fluke disease in some areas. A more accurate prediction of fluke risk will be provided in early September once August weather conditions are known. This advice will be available ahead of any necessary prophylactic treatments.

Fig 6 flock health plan

Acute liver fluke disease can be controlled by effective drugs administered at the correct time as directed by the farmer's veterinary surgeon as part of the flock health plan.  However, evasion strategies should also be adopted wherever possible by not grazing potentially contaminated, poorly drained areas.

  • Farms with a known liver fluke problem should treat sheep with triclabendazole in September if wet conditions prevail for the rest of the summer, providing that Triclabendazole resistance has not been previously diagnosed.  Triclabendazole is the drug of choice because it is effective against very young immature flukes.  Repeat treatment may be necessary 4-6 weeks later.
  • Sheep with severe acute fluke may simply be found dead without prior signs of illness.
  • The effectiveness of fluke treatments should be monitored by your veterinary surgeon and strategies using alternative flukicide products should be included later in the year to overcome potential triclabendazole resistance problems.
  • Flocks with no previous evidence of fluke disease must maintain their farm's biosecurity especially with respect to purchased sheep.
  • August and September are the peak months for lungworm disease (husk; hoose).
  • Adult cattle which have not built up immunity through natural challenge in previous years are also susceptible to lungworm.
  • Any animal showing coughing at rest and an increased breathing rate should be investigated for the presence of lungworm.
  • Testing for the presence of Dictyocaulus larvae in faeces can be readily undertaken by your veterinary practice with results available within 24 hours.
  • Note that clinical signs of lungworm may be present before the infestation becomes patent (larvae present in faeces).



  • Type 1 ostertagiosis presents in growing cattle with profuse diarrhoea suddenly affecting a large percentage of the group.

Fig 7 type 1 ostertagiosis

Diarrhoea and rapid weight loss caused by type 1 ostertagiosis.


Local farm conditions may vary so consult your veterinary surgeon. Parasite control should be part of your veterinary health plan.