Skip to Main Content
View all Diseases

Parasitic gut worms (cattle)

About Parasitic gut worms (cattle)

Gastro-intestinal worms are picked up by grazing cattle and can impact directly on cattle health, productivity and, ultimately, profitability.

Infection with gastrointestinal worms can lead to a condition known as parasitic gastroenteritis (PGE) in all ages of cattle but with first-season grazing calves being highly susceptible. Severe PGE is characterised by signs such as loss of appetite, weight loss and diarrhoea, which in some circumstances can lead to death. However, in most cases of PGE, only occurs as a subclinical infection which is seen with livestock performance well below full potential.

Susceptibility to parasite infections is influence by a wide range of factors, including; age of animals, calving times, pasture management, previous grazing history and exposure to parasites.  Control of gutworms is therefore dependent on the system (dairy or beef) but is best achieved through pasture management, nutrition and careful use of anthelmintics (wormers).

Anthelmintics (wormers) are one of the major control option available for the treatment of gastro-intestinal roundworms; however, the worms are developing resistance to some of these anthelmintics.

The financial cost of PGE in cattle is however difficult to calculate. Costs include treatment, increase in labour to administer the treatment as well as overall animal health and production losses.

The principal parasite species involved in parasitic gastroenteritis in cattle are:

Scientific name Common name
Ostertagia ostertagi Brown stomach worm
Cooperia oncophora No common name
Haemonchus species Barbers’ pole worm
Nematodirus species Thread necked worm


Ostertagia ostertagi and Cooperia oncophora are the most common species to infect cattle in the UK.  Ostertagia ostertagi live in the stomach whilst Cooperia oncophora is an intestinal species.

Watch our short animated film, War of the Worms, which highlights the important elements involved in the development and spread of anthelmintic resistance as well as the crucial messages on sustainable methods of worm control.

Key points

  • There are a variety of roundworm species that can cause disease in cattle
  • Lungworm and liver fluke may also be a problem on your farm and may also need controlling
  • Grazing stock can take up to two grazing seasons to acquire adequate immunity and thus young calves are at greatest risk of succumbing to infection
  • It is essential to conserve efficacy of existing wormers through correct usage
  • Undertake post drench efficacy checks to determine whether eggs are still present in the faeces of treated animals (generally counts are done 14 day post treatment). Faecal egg count reduction tests can be used if there are concerns about wormer efficacy.
  • Treat bought-in stock and animals that have been grazed off farm with wormers from both the 1-BZ and 2-LV classes of drugs and where possible yard for at least 24-48 hours prior to turnout
  • Turn out quarantine treated stock onto dirty pastures to ensure that any resistant surviving worms form a minor proportion of the total on pasture population
  • With your veterinary practitioner/health advisor, plan a strategic parasite control program that will reduce unnecessary treatments.
  • Avoid frequent drenching by integration with grazing management
    The relationship between nutrition and parasitism is critical; poorly fed animals have difficulty in developing and maintaining immunity to worms

Research at Moredun

  • Drug sensitivity of Ostertagia to currently available anthelmintics
  • Changing epidemiology of cattle parasites in the UK

Further information

NADIS publishes a monthly Parasite Forecast for farmers and livestock keepers, based on detailed Met Office data. The Parasite Forecast outlines the parasitic challenge facing cattle and sheep in the different UK regions.

Control of Cattle Parasites Sustainably (COWS) is an industry stakeholder group which aims to promote best practice in the control of cattle parasites. It has a wealth of free information for vets, SQPs and farmers about how to control parasitic gut worms and liver fluke in cows. For more information – visit the COWS website

Our Experts

Dave Bartley


Fiona Kenyon


Join the Moredun Community

Contribute to the Moredun community, and together we can help make a difference to livestock health. View newssheets and updates online.

Sign up