Cattle farmers should 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, says Westpoint farm vet Emily Francis based in Winchester.

“Where nutrition is good and there are no other diseases present, gastro-intestinal worms are the main factor in determining growth rate at grass,” says Ms Francis. “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.”

Ms Francis continues: “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).”

Referring to the recently updated chapter on roundworm control in the Control of Worms Sustainably (COWS) guide, Ms Francis says that 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 and animal growth rate losses from worm infection.

“Boluses that sit in the rumen and pulse treat throughout the spring kills the parasites picked up, reducing pasture contamination. But 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 that has shorter persistence of three to six weeks, can be given at turnout and then repeated six to eight weeks later if needed.

Bear in mind that using these products at or soon after turnout, may interfere with any lungworm vaccination that has been given.

“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.”

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



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