Controlling, monitoring and treating worms in cattle

Our guide will help you to maintain effective worm control in cattle. This can help to preserve the activity of wormers for future use.

Top tips for controlling roundworms in cattle

Identify risk

  • Pasture risk
  • Consider the age of stock and time of year
  • Use farm history


  • Growth rates
  • Use diagnostic tests


  • Grazing strategies
  • Strategic anthelmintic use to minimise pasture contamination
  • Therapeutic anthelmintic use based on monitoring stock
  • Housing treatments

Avoid resistance

  • Avoid treating cattle unnecessarily
  • Always weigh cattle to avoid underdosing
  • Check dosing equipment regularly to ensure the precise dose is delivered
  • Use the right product at the right time

Problems caused by worms

Cattle can be infected with several species of roundworms when grazing pastures.

The most common are Ostertagia ostertagi (stomach worm), which live in the abomasum, and Cooperia oncophora (intestinal worm), which inhabit the small intestine.

You can find these worms on all cattle farms where animals have access to grassland, even when only for short periods.

Whilst these parasites are common, clinical disease is generally only seen in young calves during their first grazing season when control has been inadequate.

Growth rate in youngstock

In youngstock, worms can reduce growth rate by up to 30%, even with a low level of worm challenge. This makes it difficult to achieve growth targets for beef animals or replacement heifers.

Even in adult cows, which are likely to be more immune to worms than calves, infections can cause up to a 1 kg per day drop in daily milk yield.

Key concerns

  • Roundworms are found on all cattle pastures
  • Disease mostly seen in calves and young cattle
  • Can reduce growth rates by 30%


Surveys and reports from sheep farms in the UK suggest that resistance to the first three groups of anthelmintics is increasing. Most sheep farms have some resistance to the white (1-BZ) group; resistance to the other two older groups is less common but increasing year-on-year.

So far, resistance in cattle worms is relatively uncommon in this country. However, there have been reports of some roundworm resistance to the clear (3-ML) group.

Following the COWS (Control of Worms Sustainably) guidelines for responsible anthelmintic use will help ensure treatments remain effective now and in the future.

Only treat cattle when needed and weigh to ensure they receive the correct dose.

Sustainable control plan

A successful worm control plan includes regular weighing of stock, effective quarantine and a targeted approach to treatment.

Learn more about worm control plans

High risk periods at pasture

Creating a map of your grazing platform and assigning a risk value to it, then grazing appropriately, can help you decide how you use your paddocks and reduce the risk of heavy parasite burden year-on-year.

Read more about high-risk periods

Useful links

Find out more about the Control Of Worms Sustainably (COWS) programme

Controlling worms and liver fluke in cattle for Better Returns manual

If you would like to order a hard copy of the Controlling worms and liver fluke in cattle for Better Returns, please contact or call 0247 799 0069.