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NADIS Parasite Forecast - July

Use of meteorological data to predict the prevalence of parasitic diseases

PF Capture


Mean UK monthly temperatures and rainfall from December 2013 to May 2014 have been above the 1961-1990 monthly averages. May was another warmer than average month with a UK mean temperature of 11.2 °C, which is 0.9 °C above the 1981-2010 long-term average and received 143% of average rainfall. (

July Parasite Forecast/Update

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



  • Peak pasture larval contamination occurs in the next two months, July and August, resulting from larvae that have developed from eggs passed by lambs.
  • High larval challenge is associated with wet summers and therefore a higher than usual PGE incidence may be seen this summer.
  • Ewes treated with a persistent anthelmintic (e.g. moxidectin) at lambing time may now be contributing to pasture egg and larval contamination as the effective period of the anthelmintic has expired. It would be prudent to check faecal worm egg counts. A pooled sample from 10 to 12 animals would suffice.
  • Pasture that has not yet been grazed by sheep (e.g. silage aftermath) may be regarded as 'safe pasture' and is best used for fattening weaned lambs.
  • In general, if lambs are to be dosed and moved to 'safe pasture' (e.g. silage aftermath) at weaning, around 10 per cent of the strongest lambs should be left untreated to carry some anthelmintic-susceptible worms over onto the new pasture to avoid heavy selection for anthelmintic resistant strains of worms.
  • Lambs grazing contaminated pastures will need anthelmintic treatment(s) to limit the build-up of infective larvae on pasture and subsequent challenge.
  • Developing larvae cause diarrhoea and poor weight gain in lambs - FWECs may be low initially.
  • The pre-patent period (interval to egg-laying by adult worms following larval ingestion) is around three weeks.
  • Remember to include rams in the farm's parasite control programme because they are fully susceptible to PGE.
  • Tapeworm segments are commonly seen in faeces passed by lambs at this time of year but are of no clinical significance.

Fig 1

Tapeworm segments, commonly seen in faeces passed by lambs, are of no clinical significance.

Targeted anthelmintic treatment
  • Targeted anthelmintic treatment selects only those lambs for treatment that are failing to meet expected growth rates.
  • Lambs are weighed every 3-4 weeks.
  • In general, around 40-60 per cent of lambs require treatment which saves money on drugs.
  • Targeted anthelmintic treatment also reduces the likelihood of selecting for resistant strains of worms because a large percentage of lambs are not treated.


  • Record ewe body condition scores.
  • Check for flystrike lesions in ewes - act sooner next year if infested.
  • Use topical products to deter flies from skin cuts.
  • Present any sheep with firm subcutaneous swellings (possible caseous lymphadenitis lesions; CLA) for veterinary examination.

Fig 2

Flies on shearing cut causing disturbed grazing and weight loss.

Fig 3

This shearing cut is slow to heal because of feeding nuisance flies.


  • Blowfly strike is a major risk from June onwards.
  • High cis cypermethrin pour-on preparations provide protection against fly strike for 6 to 8 weeks at the site of application but require re-application in most situations.
  • Cyromazine, applied before the risk period is effective against blowfly strike for up to 10 weeks after topical application.
  • Dicyclanil affords up to 16 weeks full body protection.
  • Dimpylate (diazinon) dips are effective against blowfly strike for up to six weeks.


Fig 4

Discoloured wet wool to the right of the ewe's tail head caused by a flystrike. The next wave of flies are visible on the tail.


Fig 5

Neglected flystrike lesion over the tail head.


  • Outbreaks can occur in spring-born beef calves at pasture associated with contaminated surface water and streams.
  • Large percentage of calves affected.
  • Signs include sudden onset of profuse foetid diarrhoea containing mucus and some flecks of fresh blood.
  • Considerable faecal staining of the perineum and tail.
  • Straining with possible rectal prolapse.


  • Incidents of type 1 ostertagiosis in cattle peak during August and September.
  • There is acute onset profuse diarrhoea that quickly affects most cattle in the group.

Fig 6

Sudden onset profuse diarrhoea affecting a yearling Holstein heifer at grass during September.


  • Lungworm disease appears from June onwards in unvaccinated calves, those cattle without an effective anthelmintic programme, and naïve adults.
  • Dose and move to other pastures strategies and suppressive anthelmintic treatment regimens that do not last the whole grazing season may allow conditions for lungworm disease to occur late in the season especially if conditions are wet.
  • Early signs of lungworm include coughing, initially after exercise then at rest, and an increased respiratory rate.
  • Affected cattle rapidly lose weight and body condition.
  • Prompt anthelmintic treatment is essential.
  • Levamisole (Group 2-LV) is preferred to Group 1-BZ anthelminitics.
  • In dairy cattle certain Group 3-ML compounds have zero milk withhold.

Fig 7

Early clinical signs of lungworm in a beef cow - the source of lungworm was purchased store cattle which did not receive any quarantine treatments.


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