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NADIS Parasite Forecast - November


At the start of September, north-westerly winds brought cool and showery weather to the UK. After this, the weather was dominated by high pressure from the 5th until the 11th and again from the 25th onwards, which mostly brought dry weather with plenty of sunshine, especially near the end of the month. However, the weather was rather changeable from the 12th to the 24th, and despite the two fine spells, it was a generally cool month. The fine spell during the last few days brought warm days but also some notably cool nights. (

November Parasite Forecast/Update

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


September proved to be a much drier month than average with less than half the usual amount of rain in most regions.  Such dry conditions in September have resulted in a downward revision of liver fluke risk in some regions but 'a potentially high to very high liver fluke disease risk' still prevails in western Scotland and North West England.  Predictions for Wales, western regions of England, and eastern Scotland are for moderate to high risk.

The October parasite forecast carried the treatment recommendations detailed below which were correct for Scotland but may have been over-cautious for some regions however this is the precautionary nature of disease predictions. Farmers are reminded to consult their local veterinary practitioner because local conditions may vary from the generalised regional forecasts present here and knowledge of risks factors on your own farm are very valuable in developing a disease control plan.

  • It is almost certain that prophylactic treatment with triclabendazole during September/early October will be necessary on those farms in Scotland where there is a history of liver fluke disease, and highly likely in northwest and southwest England, and Wales to prevent acute and subacute liver fluke disease.

The recommendations for liver fluke treatments for November/December are:

  • A second treatment with triclabendazole is recommended in November for western Scotland and North West England where there remains a potentially high to very high liver fluke disease risk.
  • A second treatment with triclabendazole may not be necessary in Wales, western regions of England, and eastern Scotland and liver fluke treatment in November/December should consider the use of either closantel or nitroxynil to reduce the risk of selection for triclabendazole resistance.

  • Sheep moved to low risk pastures following their first treatment may not require further treatment.

Parasitic Gastroenteritis (PGE)

  • The dry weather during September and early October may have prevented nematode larvae from either leaving the faecal mass, or migrating onto the herbage. Contaminated pastures will become infective after wet weather when a flush of infective larvae will appear on the pasture and this may be dangerous for grazing stock.
  • Outbreaks of trichostrongylosis are often seen from late October onwards in store and replacement lambs, and sometimes gimmers.  Heavy infestations can cause black foetid diarrhoea with associated rapid weight loss.
  • As the weather becomes colder, most acquired Haemonchus larvae will inhibit in the abomasal wall of the host sheep resuming development again in the spring if left untreated.  Treatment will be indicated in those flocks with a history of haemonchosis; note that arrested larvae will not produce eggs.

PF Nov F1

Trichostrongylosis is often seen in late autumn/winter in store and replacement lambs
Nov PF F2
Trichostrongylosis can also affect gimmers in late autumn/winter

Consult your veterinary surgeon regarding the possible use of Group 4 (monepantel) or Group 5 (derquantel and abamectin) anthelmintics at this time of year to prolong the efficacy of the more commonly used Group 1-3 anthelmintics.

  • Anthelmintics belonging to Groups 4 and 5 are essential in those flocks with confirmed triple-resistance (all anthelmintics in Groups 1-3).
  • Use of Groups 4 and 5 anthelmintics could also be considered when moving fattening lambs onto catch crops where the refugia concept not important because the land will be ploughed for crops next year.

Nov PF F3

Consult your veterinary surgeon about using Groups 4 and 5 anthelmintics before moving fattening lambs onto catch crops.

Anthelmintic treatments around tupping time

  • In general terms, anthelmintic treatment pre-tupping should be targeted at leaner ewes, gimmers, or those sheep with dags.  Ask your vet to investigate individual cases of poor body condition score (more than 1.5-2 condition score units less than flock average value; scale 1-5).
  • Rams have often be neglected throughout the summer months with respect to parasite control and a faecal worm egg count will decide whether a pre-tupping anthelmintic treatment is necessary.

Nov PF F4

Anthelmintic treatment should be targeted at leaner ewes and those sheep with dags. Invesgate causes of poor condition in individual sheep.

PF Nov F5

A pooled faecal worm egg count will decide whether your rams require a pre-tupping anthelmintic treatment.


  • Outbreaks of lungworm may occur after prolonged dry weather when sudden heavy rain, especially thunderstorms, releases infective larvae that have been locked up in faecal pats.
  • Growing cattle housed after their first or second season at pasture should be treated with either a Group 1 or 3 anthelmintic at housing.

Liver Fluke

  • Cattle exposed to liver fluke infection should be dosed after housing.
  • When using combination products such as closantel and ivermectin, the timing of treatment must relate to closantel (seven weeks after housing) as too early treatment after housing will be ineffective against early stage flukes.
PF Nov F6
Severe liver fluke infestation.  Treatment of cattle with closantel must be delayed until at least seven-eight weeks after housing.

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