Worms and rotational grazing – what’s the risk?

Worms and rotational grazing – what’s the risk?

Pasture management is an essential component of parasite control, particularly because it is estimated that 95% of parasites are on the pasture, and only 5% present in the animal1.

Rotational grazing strategies are an effective means to maximise beef/dairy production from grass, but the age of stock and their levels of immunity to worms can mean they are exposed to a much higher risk of parasitic disease and production loss.

If your paddock rotations last around two to three weeks, be mindful that cattle will be returning to the pasture just as worm larvae contamination reaches its peak.

You can take steps to reduce the risk of a high worm challenge, by:

  1. Limiting the exposure of youngstock to worms by prioritising your lowest risk pasture for these groups of animals, and/or move them to lower-risk pasture later in the summer.
  2. Rotate cattle out of a pasture before they eat the grass down to an extreme. 80% of parasites are found concentrated within the first 5cm of grass, so keeping grass length long means fewer worm larvae will be ingested.
  3. Reducing stocking density. This can help reduce the quantity of worm larvae ingested, since cattle won’t have to graze near to dung pats where higher numbers of worm larvae are found.
  4. Ensuring a that a subpopulation of refugia is maintained on pasture and in cattle by not treating all animals in the herd at the same time.
  5. Incorporating diagnostic tests (e.g. faecal egg counts, bulk milk ELISA tests, and regular weighing of youngstock) to better understand your herd’s parasite burden and help identify individual animals or groups of animals that can be prioritised for treatment.

For more information, talk to your vet or SQP, or visit the Beat the Parasites website.


  1. Herd, R. Strategies for Nematode Control in Cattle. Modern Veterinary Practice, 1985.

An educational service from Boehringer Ingelheim Animal Health UK Ltd (“BI”). Further information available from BI, RG12 8YS, UK. The steerhead logo is a registered trademark of Boehringer Ingelheim Animal Health France SCS, used under licence. ©2022. All rights reserved. Date of preparation: Aug 2022. UI-BOV-0093-2022. Use Medicines Responsibly.

4th August 2023

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