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NADIS Parasite Forecast - August

Use of meteorological data to predict the prevalence of parasitic diseases

PF Capture

 

Temperatures for June were above average across the UK, with warm days and mild nights, although there were no spells of exceptional warmth. It was rather unsettled early and late in the month, with localised thundery downpours on several days, but there was a period of fine anticyclonic weather around the middle of the month, bringing plenty of warm, dry, sunny weather (www.nadis.org.uk).

August Parasite Forecast/Update

The most recent version of this monthly parasite forecast may be accessed at www.nadis.org.uk.

CATTLE NEMATODES

  • Lungworm disease (husk, hoose) reaches a peak in August.
  • Unvaccinated dairy calves at grass for their first season without an appropriate parasite control programme are most at risk.
  • Weaned beef calves are typically most at risk during their second grazing season.
  • Adult cattle may show clinical signs after grazing heavily contaminated pastures.
  • Frequent coughing, even at rest, is the most common sign of lungworm.
  • Most cattle in the group will develop clinical signs within several days if left untreated.
  • Affected cattle rapidly lose weight and body condition.
  • First stage larvae are passed in faeces not eggs therefore patent infestation will not be detected using the usual McMaster technique.
  • Clinical signs may be present before lungworm larvae are detected in faeces.
  • There is a rapid response to anthelmintic treatment except for severely affected cattle which may have suffered physical lung damage.

 

Fig 1

Frequent coughing, even at rest, is the most common sign of lungworm.

Fig 2

First stage larvae are passed in faeces therefore patent infestation will not be detected using the usual McMaster technique for worm eggs.

Ostertagiosis

  • 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.
  • Affected cattle rapidly lose weight and body condition.
  • Immediate treatment of all cattle in the group is important when first signs of acute profuse diarrhoea appear.

Fig 3

SHEEP NEMATODES

Advantages of early lamb sales

  • Lambs sold before mid-July will largely have avoided PGE challenge and needed very few anthelmintic treatments.
  • Selling lambs before mid-July avoids the peak of the blowfly season.
  • Selling lambs before about five months old also avoids most trace element deficiency problems.
  • Lamb prices will soon begin to fall as more lambs become available.

Advantages of safe pastures for weaned lambs

  • After a move to safe grazing, lambs may not need to be treated for 6-10 weeks, however, this depends upon many factors including the amount of infection carried over, stocking rate and weather conditions.
  • Monitoring a pooled faecal worm egg count (FWEC) every 7-10 days with fresh faeces collected from around 10 lambs after gathering into a corner of the field can help to decide whether anthelmintic treatment is necessary.
  • PGE may become a problem in the autumn if lambs are returned to pastures heavily contaminated by worm eggs in the previous months.
  • Where weaned lambs must remain on pasture previously grazed by sheep this year, further pasture contamination with eggs passed by the lambs must be limited by anthelmintic treatment to achieve acceptable future growth rates.

Overcoming problems of contaminated pastures for weaned lambs

  • Consider using targeted anthelmintic treatments whereby only those lambs failing to grow at accepted rates are treated.
  • Targeted anthelmintic treatments avoid unnecessary treatments (up to 40% on average), save money, and reduces the selection pressure for resistant strains of worms.
  • Under-dosing lambs will lead to poor drug efficacy and may select for resistant strains of worms.
  • Drug dosages should be calculated for the heaviest in the group, not the average weight. Use weigh scales not estimates.
  • It is important to calibrate dosing equipment.
  • Cobalt deficiency should be considered as a potential cause of poor growth in weaned lambs as well as PGE.  Your veterinary surgeon should be consulted for professional advice.

Ensuring correct anthelmintic treatments

  • Under-dosing lambs will lead to poor drug efficacy and may select for resistant strains of worms.
  • Drug dosages should be calculated for the heaviest in the group, not the average weight. Use weigh scales not estimates.
  • It is important to calibrate dosing equipment.

Potential complicating factors

  • Cobalt deficiency should be considered as a potential cause of poor growth in weaned lambs as well as PGE.  Your veterinary surgeon should be consulted for professional advice.

Fig 4

Lambs off to market in July.

Fig 5

Excellent quality March-born lambs ready for market in early July.

Fig 6

PGE may also become a problem in the autumn if lambs are returned to pastures heavily contaminated by worm eggs in the previous months.

Fig 7

Around 10 per cent of the heaviest lambs without diarrhoea in the group should be left undosed to carry some anthelmintic-susceptible worms onto safe pasture.

Fig 8

Wherever possible, lambs should be moved onto safe grazing such as silage aftermath after weaning to avoid parasite challenge.

Fig 9

Lambs should be dosed for the heaviest lambs in the group.

Fig 10

Lambs may not need to be treated for 6-12 weeks after a move to safe grazing.

BLOWFLY STRIKE

  • The risk of blowfly strike will continue throughout August in lambs but will be much less likely in adult sheep following shearing.
  • Flystrike on the back related to rain scald has been seen in previous wet summers.  Control of PGE will reduce faecal soiling of the tail and perineum.
  • Control measures using either dips or pour-on preparation for lambs will now largely depend upon meat withhold times.

Fig 11

Blowfly strike affecting the lamb on the right. Evidence of faecal staining of the perineum probably indicates lack of effective PGE control in both ewes and lambs.

Fig 12

Severe lumpy wool which has attracted blowflies as well as nuisance flies causing severe weight loss in this ewe.

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