Housing is a useful point to review the parasite challenge cattle faced at grass.

Peter Howard, veterinary adviser at Boehringer Ingelheim explains that grazing history, performance records, testing and previous treatments can all help farmers and their vets decide what action is needed now, and what should change next year.

He said: “Housing is sometimes treated as a date in the dosing calendar.

Cattle may be brought into sheds carrying gutworm, lungworm and/or liver fluke infections without showing obvious signs.

At the same time, not every group of cattle will have faced the same challenge at grass.

The age of the animal, grazing history, weather, stocking pressure, and previous treatments given over the spring and summer can all affect the level of parasite risk.

It is important for farmers to remember that since December 1, 2025, all antiparasitic medicines for food producing animals in Ireland require a veterinary prescription.

"It can also help reduce unnecessary treatments for parasites that may not be present,” Howard said.

Review risk by group

Review cattle group by group rather than assuming the same plan is right for the whole herd.

Which fields did each group graze, for how long, and what is the grazing history of those fields?

Were young cattle moved onto fields cut for hay or silage later in the season?

Were any new animals purchased, and could they have brought in a different parasite risk onto the farm?

Look back at when wormer treatments were given, which active ingredients were used, and whether cattle were weighed and dosed accurately.

Did you have any concerns about whether the product had worked after treatment?

Performance records add to the overall picture. Poor weight gain, loss of condition, scouring, coughing, or a drop in milk yield may all need investigation.

“These issues are not proof of a parasite burden on their own, but they can help the vet interpret test results and assess the risk,” Howard said.

What did monitoring show?

“You can’t identify a sub-clinical worm burden just by looking at an animal.

"It’s why testing is such a useful tool, and can help you and your vet understand the risk your cattle have faced this season,” Howard said.

For calves and young cattle in their first season at grass, faecal egg counts (FECs) can show how adult gutworm egg output changed during the season, and what level of worm burden they have likely been carrying.

Regular samples every two weeks from turnout are more useful than one isolated result because the trend can show when pasture challenge was increasing.

Results can be considered alongside recorded liveweight gain, grazing history, and any worm treatments already given.

In adult dairy cows, immunity can keep gutworm egg counts low, so routine faecal egg counting is less informative.

A bulk tank milk ELISA test can instead indicate the milking herd’s level of exposure to the gutworm Ostertagia ostertagi by detecting antibodies.

It is important to remember that a bulk milk test is a herd or group level monitoring test.

It cannot identify individual cows that require treatment. Timing of the test also matters because antibodies can remain for several months after treatment.

Lungworm is not detected by an ordinary gutworm faecal egg count, so any coughing during late grazing or shortly after housing should be acted on quickly.

Lungworm needs prompt veterinary investigation and treatment if confirmed, to reduce the impact on lifetime performance.

Use the review to plan ahead

“The aim is not to collect test results for their own sake,” Howard said.

“When you combine test results with what happened on the farm it can help you make better decisions on what to do now, and if any changes need to be made for the next grazing season.”

Look at whether cattle performed as expected, did treatments appear to work, and did the same fields or groups of animals repeatedly experience problems.

This may identify where closer monitoring, different grazing management, or a change in the treatment plan is needed next season.

Housing provides an opportunity to discuss the evidence with your vet and decide which parasites need to be targeted, which groups of animals need treating, and whether further testing or changes in management practices would be useful.