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NADIS Parasite Forecast - March

Published 12th March 2015 | Article by NADIS

NADIS Parasite Forecast - March

Use of meteorological data to predict the prevalence of parasitic diseases

Parasite forcas map

For much of January, the UK was under the influence of a westerly weather type, with a sequence of Atlantic depressions tracking across the country. A sequence of particularly deep lows between the 9th and 15th brought some very stormy conditions to Scotland, especially the Western and Northern Isles, as well as plenty of rainfall. The first half of January was very mild, but the second half was colder, with mostly quieter weather but some snowfalls at times, especially across high ground in the north. There were some sharp frosts with temperatures lower than at any time earlier in the winter or during the whole of last winter. (

March Parasite Forecast/Update

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


  • Parasite control for this year's grazing season must be planned now.
  • Control measures must be formulated on an individual farm basis.
  • 'Safe grazing' for sheep at turnout is defined as last year's pastures grazed by cattle or re-seeded pastures (i.e. not grazed by sheep).
  • Forward planning must maximise the use of safe grazing.
  • The principle aim of parasite control around lambing time is to minimize the future contamination of pastures by eggs passed from adult parasites in the gut of the ewes. When deposited on pasture, these eggs hatch and develop into infective larvae causing disease in lambs.
  • Egg output is much reduced in well fed ewes in good condition.
  • Most sheep farms wean a lamb crop around 155% - therefore approximately one half of the flock nurses only one lamb.  If safe grazing is not available for all ewes, ewes with single lambs should graze contaminated pastures with safe grazing reserved for ewes with twins.

Control measures recommended for sheep on 'safe grazing'

  • The 'peri-parturient rise' in faecal egg production by ewes and future contamination of pastures can be controlled by a short-acting anthelmintic given before ewes are turned out onto 'safe grazing'.
  • In order to avoid undue selection for anthelmintic resistance, SCOPS recommends that this anthelmintic treatment is targeted and not all ewes are treated such that some anthelmintic-susceptible parasites are carried over onto the safe grazing.
  • This anthelmintic regimen should be targetted to include the following sheep:

Glimmers and young ewes

Ewes nursing twins and triplets

Ewes in low body condition


Fig 1

Ewes in good condition and those nursing singles should not need anthelmintic treatment before turnout onto safe grazing.


Fig 2

All ewes nursing multiple litters and those in poor condition should be treated with a short-acting anthelmintic before turnout onto safe grazing.


Sheep grazing contaminated pastures

  • Ewes turned onto contaminated pastures should be treated with a persistent anthelmintic to prevent immediate re-infection of the ewes with larvae from the pasture.

Be aware of the need for nematodirosis control and plan ahead

  • Nematodirosis caused considerable production losses in young lambs grazing contaminated pastures in late spring/early summer on many farms in 2013.
  • Lambs grazing safe grazing are not at risk from nematodirosis.
  • Plan ahead and use safe grazing wherever possible to remove the risk of this disease.
  • Follow disease forecasts for April and May on the NADIS website to determine the risk of nematodirosis in 2015.

Fig 3

Nematodirosis affecting lambs grazing contaminated pasture - note only the lambs are scouring, the ewes are unaffected.

Fig 4

Production losses from nematodirosis can be considerable yet are easily avoided.


Fig 5

Lambs grazing 'safe grazing' are not at risk from nematodirosis.

Plan ahead to prevent lungworm disease in cattle

Fig 6

Lungworm disease is typically seen in grazing cattle from July onwards (see below).

  • Plan now with your veterinary adviser to prevent lungworm disease in cattle.
  • Lungworm disease is typically seen in grazing cattle from July onwards.
  • There are several anthelmintic control strategies that can be used on set-stocked systems using including depot injection and strategically-timed injections, and either pulse release or slow delivery boluses.
  • Anthelmintic control strategies for lungworm will aid control of gut parasites particularly ostertagiosis.
  • Vaccination of cattle over two months old against lungworm requires two doses four weeks apart with the second dose at least two weeks before turnout or weaning.
  • Cattle with a history of respiratory disease should not be vaccinated against lungworm.

Fig 7

Death caused by severe lungworm infestation with large numbers of worms in the airways of a yearling stirk.


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