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Test before treating heifers at housing (Oct 2021)

Treating young heifers with broad-spectrum products to kill a range of parasites may not be the most sensible approach.


It can be tempting to buy and apply a combination of worm and ectoparasite products to first-season grazing calves as they come indoors for winter. It is a quick and easy way to head off a range of potential pest problems. Job done.

But this blanket approach may not be the most sustainable way forward, according to University of Liverpool’s Diana Williams, who is a lead adviser on the Control of Worms Sustainably (COWS) group. If, for example, the liver fluke risk has been low during the summer and autumn, or lice and mites are never usually a problem, there are other treatment options against pests such as gut worms, which are worth considering.

“Treatments should be chosen according to the mix of parasites present and the levels of exposure the calves have faced while grazing,” says Professor Williams. “There are many factors to consider, including past and current weather conditions and the farm’s disease history. There is such a degree of variability between years – a ‘one size fits all’ plan will fail to meet the needs of most herds.”

Where calves have grazed high-risk pastures, such as where cattle have been grazing during the previous 12 months, roundworms are likely to be a problem. If calves are thought to have been exposed, they are at risk of ostertagiosis Type II disease later in winter. This is because calves pick up larvae in autumn that then go into an ‘arrested’ state and just sit in the gut until suddenly becoming simultaneously active. “This causes extensive damage to the abomasum, leading to diarrhoea, loss of both appetite, and body condition. The disease is acute and can lead to death,” says Professor Williams.

Where liver fluke is not a problem, a treatment with a Group 3 macrocyclic lactone will kill all roundworm larvae in the gut, including all those that are just ‘sleeping’. This treatment will also kill any lungworm that may be present.

Liver fluke

The weather this year has been unusual, with a particularly dry spell in July and August. How this will affect the liver fluke risk is uncertain and there will be wide variability between regions and farms. “It is always a good idea to test for fluke, rather than simply assuming it is or isn’t present,” advises Professor Williams. “Having the vet carry out antibody detection blood tests on the calves is usually worthwhile. Tests on milk from the bulk tank will show if the herd has been exposed to liver fluke, making testing young stock even more important.”

She adds that where results come back positive, treatments targeting all fluke stages, such as those containing triclabendazole, should be given two weeks after housing for optimum fluke control. Using broad-spectrum products to kill lice and mites in situations where ectoparasites do not cause any problems should be avoided. “An alternative approach is to use a Group 1 white drench (bendimidazole) against roundworms and then treat lice and mites later in the winter, but only if they become a problem,” says Professor Williams.

Life cycles

“Housing offers a break for parasite life cycles and is a good time to reflect on the calves’ previous months at grass and to plan for the future,” says independent

animal health specialist Sally Harmer.

“Talking through treatment options with your vet or RAMA/SQP is a good idea, as the range of products and the stages of parasites they treat varies widely. “It is vital to check that animals do need treatment by testing beforehand and to move away from using combination products if there is no need for them. This will save money and reduce unnecessary product use,” she explains.

“Knowing the animals’ weights, to avoid under-dosing, and ensuring administration equipment is up to date and correctly calibrated, will ensure products work as they should and help prevent resistance. “And staff administering the treatments should be well trained and must wear gloves, and ideally waterproofs, particularly when applying pour-on products. There must also be adequate means to restrain livestock, with appropriate cattle crushes and head scoops.”

For more information on treating all ages of dairy cattle visit the COWS website: The ‘Parasite Control Guide 2021’ produced by AHDB, lists all the available products for internal and external parasites, and is also available on the COWS website

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