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Winter Dosing Principles

Winter Dosing Principles

What is Anthelmintic resistance

The genes responsible for anthelmintic resistance are believed to be present in all worm populations but at very low levels. When animals are treated with an anthelmintic, this kills all the susceptible worms allowing only the resistant worms to survive.

The surviving resistant worms output eggs with the dung onto pasture which results in resistant worms making up a much greater proportion of the worm population in subsequent generations.



How prevalent is Anthelmintic resistance

A 2017 Teagasc survey found:

  • Resistance to benzimidazole anthelmintic (white wormers) of 75% on dairy calf-to-beef farms
  • Resistance to macrocyclic lactone anthelmintic (clear wormers) of 100% on dairy calf-to-beef farms


How to avoid resistance

  • Read the manufacturer’s instructions
  • Avoid under dosing animals, weigh cattle if possible, to get correct weight.
  • Check dosing equipment to ensure correct amount is applied
  • Avoid the continual use of wormers from the same class and only use a combination anthelmintic product when it is necessary to treat for both fluke and worms

AT this stage there is evidence of resistance to all classes.  All products within the same class have a similar mode of actions.  So, if a parasite has resistance against a class, it will be resistant against all products within that class.

When switch products we need to switch to a different class of anthelmintic not just switch between products within the same class.  Focus on the class of the products not the product name.

  • Use good biosecurity protocol for all bought in animals
  • Reduce the amount of dosing and allow the animals build immunity.
  • Take dung samples and only dose on rising counts or when animals coughing.
  • Do not dose all the animals in the group target the low weight calves and those with dirty tails.
  • After dosing leave in old paddock and move to clean pasture in 3 days
  • Extend the period between doses by using bales or silage ground
  • Dung sample before and 2 weeks after doses *1 week for the levamisoles to ensure a response to treatment



What are we trying to control within our winter dosing program?

  • Stomach worms/ Lungworm
  • Liver Fluke
  • Rumen Fluke
  • Lice + mange

Lungworm & Stomach worms
Mature cattle can build an immunity to worms.  Our main concern is weanlings and animal heading for their 2nd winter.  Mature animals should be dose if there’s an indication of a problem.

There are 3 families of drugs but only two families of drugs that give a full cover across the winter

  1. Macrolytic Lactones-Ivomec, Mastermectin, Cydectin, Eprinex etc.
  2. Albendazoles- Albex, Albencare, Tramazole etc


  1. Levamisole’s – are to be avoided in winter dosing programmes as they do not cover Type 2 ostertagia.

Liver Fluke

Adult cattle do not have immunity.  The presence of Liver Fluke depresses Liver function. This will result in reduced production, poor immunity and reduced efficacy of vaccinations.



No immunity developed.  Fill a shed at the one time.  Injectable iver- MECTINS only kill sucking lice.  Pour-ons kill both.


Weanling Treatments this winter:

  • Housing is a stressful time.
  • Try and do a pre-housing dose (3 weeks prior to housing for lungworms).
  • Over winter dose for worms, fluke and lice.
  • Combination pour-ons that kill worms and most liver fluke and lice are a good option.


Store/Finishing cattle Treatments this winter:

Over winter dose for worms, fluke and lice.  Be conscious of meat withdrawals, it ranges from 60 to 143 days with differing products.  If feeding reasonable levels of concentrates, the liver needs to be in good health.  Don’t delay fluke dose to long.


Dairy cows treatment across this winter:

If you dosed your cows this summer with Eprinex, use a different family like and albendazole this winter.  Eprinex (wormer, eprinomectin) is a macrocytic lactone like iver – MECTIN.

As it’s the only wormer with zero milk withdrawal we should be preserving its use for summer dosing.  Dectomac, noromectin and mastermectin etc are also macrocytic lactones.

Our winter worm dosing strategy should therefore be built around albendazoles like albex, albex gold


Albendazoles kill worms and mature fluke.  If using an albendazoles wait 3 weeks after housing to allow maturity of all the worms.  After 3 weeks housing the albendazoles will not kill immature fluke.

Therefore a 2nd dose will be needed later in the winter.  The 2nd dose can be a repeat of albendazole or Rumenil to kill rumen fluke, if required. If using Rumenil as 2nd dose do not use within 2/3 weeks of calving.

If using Rumenil as 1st dose avoid using at drying off.

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