Why is winter dosing important?

Housing cattle is expensive.

Farmers are investing in silage, concentrates, bedding, labour and housing, so animals need to make the most of the feed going into them.

A significant parasite burden can work against this.

Parasites may contribute to:

• Poor thrive
• Reduced daily liveweight gain
• Poor feed conversion
• Reduced appetite
• Lower milk performance
• Poor coat condition
• Coughing or respiratory problems
• Irritation and scratching
• Reduced overall animal performance

Liver fluke in particular can cause losses without cattle necessarily showing obvious clinical signs. Animal Health Ireland notes that subclinical liver fluke infection can adversely affect growth rate, milk yield and fertility. That is why parasite control should form part of the wider winter herd-health plan rather than being treated as an isolated job.

What parasites should you consider when winter dosing cattle?

There is no single "winter worm".

Several different internal and external parasites may need to be considered.

1. Stomach and gut worms Stomach worms are particularly important in younger cattle that have not yet developed strong immunity. One of the main concerns over winter is Ostertagia ostertagi. Larvae can become inhibited or dormant in the stomach wall before developing later in the winter. This is important because not every wormer is effective against inhibited larvae. Farmers therefore need to know what a product actually treats rather than selecting a product simply because it is described as a cattle wormer. Product choice should be discussed with your vet and based on the parasites being targeted, previous treatment history and evidence of resistance where available.

2. Lungworm Lungworm — commonly associated with hoose — is generally picked up while cattle are grazing. Heavy infections can damage the lungs and leave animals more vulnerable when moving into the housed environment. Where lungworm treatment is required, Teagasc advises that treatment can be carried out before housing to give the lungs time to recover before cattle enter a potentially dustier indoor environment. Coughing should never automatically be assumed to be lungworm, particularly after housing. Respiratory disease can have several causes, so seek veterinary advice where cattle are coughing, breathing heavily or showing signs of illness.

3. Liver fluke Liver fluke is one of the biggest considerations in an Irish winter parasite-control programme. The parasite is associated particularly with wet ground and areas that support the mud snail involved in its lifecycle.

Cattle usually pick up infection while grazing, particularly later in the grazing season. Once inside the animal, liver fluke progress through different stages:

Early immature fluke → Immature fluke → Adult fluke The process takes roughly 11–12 weeks. This matters because different fluke treatments kill different stages of the parasite. Why timing your fluke treatment matters

A product that kills adult fluke may be very effective when used at the correct time but may have little or no effect on immature fluke shortly after housing. Other active ingredients can target immature stages, while some can target earlier stages.

This is why asking:

What is the strongest fluke dose?"is usually the wrong question.

A much better question is:

What stage of fluke am I trying to treat, and when should this particular product be used?

That simple change in thinking can make a major difference to the effectiveness of a winter dosing programme.

When should cattle be dosed for liver fluke?

There is no single correct date for every farm.

The ideal timing depends on:

• When cattle were housed
• Farm history
• Fluke risk
• Weather and grazing conditions
• Diagnostic results
• The active ingredient being used
• The stages of liver fluke that the product controls

As a general principle, products targeting earlier immature stages may be suitable earlier in the housing period, while treatments that only target adult liver fluke normally need to be given later, once the parasites have matured.

Some adult-only treatments may therefore be most effective approximately 10–12 weeks after housing, whereas products effective against immature stages may be used earlier. Always follow the veterinary prescription and the individual product instructions.

4. What about rumen fluke? Finding rumen fluke does not automatically mean cattle need treatment.

Rumen fluke can occur on wetter farms, but infection does not cause significant production problems in the majority of cases. Routine dosing simply because rumen fluke eggs have been detected may therefore be unnecessary. If rumen fluke is suspected of causing a clinical problem, discuss the results and animal performance with your veterinary practitioner before treating.

5. Lice and mange during winter housing Not every winter parasite comes from grass.

Housing creates ideal conditions for external parasites such as biting lice, sucking lice and mange mites to spread between cattle.

Watch for:

• Cattle scratching against gates or barriers
• Excessive licking
• Hair loss
• Rough coats
• Restlessness
• Areas of irritated or damaged skin

Close contact between animals makes transmission easier, and lice problems often become more noticeable later in the winter.

If treatment is needed, it is important to consider the whole group. Leaving untreated cattle in contact with treated animals can allow re-infection to occur. Clipping cattle along the back may also help reduce sweating and can aid the correct application of certain pour-on products where appropriate.

Should every cow be dosed at housing?

Not necessarily.

Modern parasite control should be based on risk rather than simply repeating the same routine every year.

Consider:

• Animal age
• Grazing history
• Previous dosing
• Previous faecal egg count results
• Liver fluke history
• Factory or Beef HealthCheck reports
• Animal performance
• Farm location and land type
• Previous problems with treatment effectiveness

Young cattle are generally more susceptible to stomach and lungworms than mature animals. For adult cows, the parasite-control programme may be quite different from the programme required for first-season grazing cattle or weanlings.

Faecal egg counting: know what you are treating

One of the most useful changes farmers can make is to test rather than guess.

A faecal egg count, or FEC, examines dung samples for parasite eggs and can help identify whether certain worms or fluke are present.

This can help answer important questions such as:

• Do my cattle actually need treatment?
• What parasite am I trying to control?
• Has the treatment I used worked?
• Could resistance be developing on my farm?
• Can a faecal egg count detect liver fluke?

Yes — but there is an important limitation.

Only mature adult liver fluke produce eggs. A dung sample taken too early after infection may therefore be negative even though immature fluke are present.

FEC results should consequently be considered alongside farm history, grazing conditions, slaughter reports, clinical signs and veterinary advice rather than being used in isolation. Faecal Egg Count testing at Feirm Supplies

Feirm Supplies provides in-house Faecal Egg Count testing for worms and fluke, helping farmers make more informed parasite-control decisions.

Our Test & Retest option also allows farmers to test animals and then check again following treatment, helping assess whether the treatment has been effective.

View our Faecal Egg Count – Worm & Fluke Test & Retest service

Anthelmintic resistance: why dosing smarter matters

Anthelmintic resistance occurs when parasites survive a treatment that would normally kill them.

Those resistant parasites then reproduce, gradually reducing how effective that treatment is on the farm.

Resistance is now an important issue for Irish livestock farmers, and it is one of the main reasons why parasite treatments should be used carefully.

The HPRA says concerns around anthelmintic and ectoparasitic resistance were a major reason behind changes to the regulation of antiparasitic medicines in Ireland.

To help protect treatment effectiveness:

• Avoid treating unnecessarily.
• Use diagnostics where practical.
• Know which parasite you are targeting.
• Use the correct active ingredient.
• Weigh animals as accurately as possible.
• Dose according to the correct bodyweight.
• Check dosing equipment before use.
• Never deliberately under-dose.
• Follow the product instructions.
• Check whether treatment has worked where resistance is suspected.
• Discuss repeated treatment failure with your vet.

Giving too little product is not a saving if it fails to clear the parasites.

Does cattle weight matter when dosing?

Yes.

Correct dosing depends on bodyweight. Underestimating an animal's weight can result in under-dosing, potentially reducing treatment effectiveness and contributing to resistance.

Where animals vary significantly in size, they should be weighed or grouped appropriately rather than assuming every animal is the same weight.

The HPRA specifically recommends determining bodyweight as accurately as possible and checking dosing equipment before treatment.

Remember milk and meat withdrawal periods

This is particularly important when treating: • Dairy cows • In-calf heifers • Cattle approaching slaughter

Withdrawal periods can vary significantly between active ingredients, products and formulations. A product suitable for one group of cattle may not be suitable for another. Never assume the withdrawal period based on a product you used previously. Always check the current product information and prescription before treatment.

Do you need a prescription for cattle wormers and fluke treatments?

Yes.

Since 1 December 2025, antiparasitic veterinary medicines for food-producing animals in Ireland require a veterinary prescription before they can be supplied. This includes many of the products traditionally used for worms, fluke and external parasites in cattle.

At Feirm Supplies, our team of qualified Responsible Persons can help make the process straightforward, working through VETPal and our network of veterinary practitioners to help farmers organise the prescription and access the appropriate animal-health products.

A simple winter parasite-control checklist

Before reaching for a dose this winter, ask: 1. What am I treating? Worms, lungworm, liver fluke, lice, mange — or is treatment actually necessary? 2. What evidence do I have? Consider FEC results, previous herd history, animal performance, slaughter reports and veterinary advice. 3. What stage of the parasite am I targeting? This is especially important for liver fluke. 4. Is the product suitable for these animals? Check age, pregnancy, lactation and other restrictions. 5. Is the timing correct? A good product used at the wrong time may give disappointing results. 6. Do I know the animals' weights? Avoid under-dosing. 7. What is the withdrawal period? Particularly important for milk and finishing cattle. 8. Has the treatment worked? Where appropriate, consider follow-up testing.

Frequently Asked Questions About Winter Dosing Cattle

When should I winter dose cattle? There is no single dosing date that suits every herd. Timing depends on the parasites being targeted, when cattle were housed, the product being prescribed and your individual farm risk. Liver fluke treatments in particular need to be timed according to the stage of fluke they control.

What should cattle be dosed for at housing? The main parasites to consider include stomach worms, lungworm and liver fluke, together with external parasites such as lice and mange. Not every herd will require treatment for all of these.

Should cows be dosed immediately after housing? Not automatically. The correct timing depends on the parasite and the treatment being used. Some treatments may be appropriate around housing while others work better several weeks later.

How do I know if my cattle have worms? Poor thrive, reduced weight gain, diarrhoea or coughing may indicate parasites, but animals can also carry infections without obvious signs. Faecal egg counting and veterinary assessment can help determine whether treatment is required.

How do I know if my cattle have liver fluke? Farm history, faecal testing, blood or milk testing where appropriate, slaughterhouse reports and veterinary assessment can all contribute to diagnosis. Remember that dung testing detects eggs from mature fluke and may not detect early immature infections.

Why might my fluke dose not work? Possible reasons include treating at the wrong time, using a product that does not control the parasite stage present, incorrect administration, under-dosing or resistance. If fluke continues to appear after treatment, review the programme with your vet. Animal Health Ireland highlighted this again in its 2026 Beef HealthCheck update. Do cattle need treatment for lice every winter? Not necessarily. Monitor animals for scratching, hair loss and irritation. Where treatment is necessary, treating the appropriate group together can help prevent untreated animals from re-infecting treated cattle. Do cattle wormers now require a prescription in Ireland? Yes. From 1 December 2025, antiparasitic medicines for food-producing animals are prescription-only in Ireland.

Make your winter dosing programme work harder

Winter dosing should not simply be another job to tick off the list.

A successful parasite-control programme means knowing what is present, choosing the right treatment, using it at the right time and checking that it has worked. The result is healthier cattle, better use of expensive winter feed and a more sustainable approach to parasite control.

Need help with your winter parasite plan?

Feirm Supplies can help with:

• Worm and fluke Faecal Egg Count testing
• Test & Retest FEC services
• Animal-health product advice
• Prescription support through VETPal and our veterinary network
• Winter dosing products
• Practical support from our qualified Responsible Persons

Talk to the Feirm Supplies team before winter dosing and make sure you're treating the right parasite, with the right product, at the right time.

Always use veterinary medicines according to the veterinary prescription, current product label and package leaflet. Speak to your veterinary practitioner for advice on your individual herd.