1st November 2021

Housing is a good time to treat calves for internal and external parasites. However,  doing what has always been done routinely in the past, may not be the way forward this year

Traditionally young calves are treated at housing with broad-spectrum products to kill a range of parasites including roundworms, lungworms, liver fluke, lice and mites.

But this blanket approach may not be the most sustainable way forward. If liver fluke risk has been low over summer and autumn, or lice and mites are never usually a problem, there are other treatment options against pests such as gut worms that 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. There are many factors to consider, including past and current weather conditions and the disease history of the farm. There is such a degree of variability between years – a ‘one size fits all’ plan will fail to meet the needs of most farms.


Where calves have grazed high risk pastures, ie where cattle have been grazing in 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 which 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.

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 lungworms 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 between farms.

It is always a good idea to test for fluke – rather than assuming it is or isn’t present. Having the vet come and do 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 the youngstock even more important.

Where results come back positive, treatments that target all fluke stages, such as those that contain triclabendazole, should be given two weeks after housing for optimum fluke control.

Lice and Mites

Using broad spectrum products that 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.

Talking through treatment options with the vet or RAMA/SQP is a very 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 the farmer money and reduce unnecessary use.