Grazing strategies for worm control

Friday, 29 May 2020

As temperatures increase, the time for worm eggs to develop into infective larvae shortens. As we move into June and July, there is an abundance of larvae on pasture.

Good grazing management can provide high-quality nutrition, which can help animals withstand the effects of parasites and can also reduce the risk of acquiring worm infections when at pasture. Consider recording pasture risk on a map to allocate grazing to different classes of stock.

Alongside assessing pasture risk, also use farm history, growth rates, forecasts and faecal egg counts to monitor the risk of worms in your stock. If you do need to treat, check out the Parasite control guide 2020 for a comprehensive list of products.


The most susceptible are weaned calves grazing for the first time, followed by youngstock in their second grazing season, on pastures that have carried cattle any time in the past 12 months. The best indicator for parasite control/treatment is liveweight gain – as a guide, aim for daily liveweight gains of at least 0.7‒0.8 kg/day at grass.

New leys, silage aftermaths and fields that have only carried sheep in the past 12 months are the lowest-risk pastures for youngstock. A leader-follower system can help to reduce the risk of worms – youngstock in their first grazing season can be grazed ahead of older cattle and moved to fresh pasture when the grass is grazed to a level that continues to provide adequate grazing for the cattle that are following on.

For more information on worm control in cattle, visit COWS has recently updated the following manuals: Control of lungworm in cattle and Control of roundworms in cattle.


Highest-risk pastures are those grazed by ewes and lambs in the previous year or grazed by store/ewe lambs in the previous autumn/winter. Maintain optimum sward heights and avoid grazing below 4 cm to minimise ingestion of infective larvae at the base of the sward. Silage aftermaths and fields that have not been grazed for 12 months provide a low-risk option to move lambs onto post-weaning.


  • Provide lowest-risk pasture for weaned lambs and consider weaning at 12 weeks to avoid larvae build-up
  • Reduce contamination on dirty pastures by grazing them with weaned ewes in good body condition

For more information on worm control in sheep, visit

Mixed grazing

If you keep cattle and sheep, reduce the level of contamination on a pasture by grazing them together – it reduces the stocking density of the host species (cattle and sheep worms are different species). However, this can make pasture utilisation more difficult, so rotating between cattle and sheep during the season may be more practical.