Cattle farmers are being advised to ensure their approach to treating youngstock for roundworms (Ostertagia and Cooperia) is sustainable, so that resistance to products does not develop in the same way as it has in sheep.

Westpoint farm vet Emily Francis says “Where nutrition is good and there are no other diseases present, gastro-intestinal worms are the main factor in determining growth rate at grass. Therefore, weighing and only treating those animals not growing as expected will give good control, reduce overall treatment and instil immunity in those not treated.”

This optimum approach can also be used in combination with assessing pasture contamination and the amount of land available for grazing youngstock. Where it is hard to avoid turning out onto contaminated grass, the animals are likely to benefit from treatment pre-turnout with a bolus or long-acting macrocyclic lactone (ML).

As stated in the recently updated chapter on roundworm control in the Control of Worms Sustainably (COWS) guide, treatments given to autumn-born calves in the first grazing season, or spring-born calves in their second, at or within three weeks of turnout, will prevent a peak of infective larvae on pastures in mid-summer.

Westpoint farm vet Emily Francis

“Boluses that sit in the rumen, and pulse treat throughout the spring, kill the parasites picked up, reducing pasture contamination. This also allows animals to pick larvae up between the pulses, which helps them gain a level of immunity, which is to be encouraged.”

“Treating with a macrocyclic lactone (ML) that has shorter persistence of three to six weeks, can be given at turnout and then repeated six to eight weeks later if needed. Bearing in mind that using these products may interfere with any lungworm vaccination that has been given.”

Ms Francis advises all farmers to set a plan at the start of the grazing season – but to review it as time goes by. “Farmers with more flexibility in their pasture rotation may be able to monitor growth, by weighing beef cattle or measuring the frame size of heifers, and only treat if growth is falling behind the expected 0.7 to 0.8kg/day.”

To determine the most appropriate products to use talk to your vet or Registered Animal Health Adviser and follow the COWS five ‘Rs’ – use the right product, at the right dose rate, on the right animal, at the right time and in the right way.

Visit the COWS website: for more information on controlling roundworms this grazing season.

Control Of Worms Sustainably (COWS) is a voluntary initiative funded by a number of industry organisations including AgriSearch.  It aims to provide the best available, evidence-based information to the beef and dairy cattle industries in relation to the sustainable control of both internal and external parasites.