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Protect your pastures: Let’s talk quarantine!


Introducing new livestock to your existing groups can be an exciting (and very busy!) time. Good biosecurity measures go a long way to reducing the risk of disease introduction and spread; but have you considered the worms? In the whirl of activity, it may be easy to overlook parasites, particularly if there are no obvious outward signs the newcomers are harbouring intruders. With some forward planning, creating a good ‘new livestock policy’ keeps the risk to resident animals at a minimum and provides a robust defense against pasture contamination.

This article will focus on how to protect your pastures from resistant gastro-intestinal worms and is intended as a general guide. Always discuss any herd or flock health plans with your veterinarian to ensure the right approach is tailored to your farm.


1. What to do with new arrivals

Keep any newcomers away from your established groups for a quarantine period of 3 weeks; this allows time to observe and treat disease before it has a chance to spread. This applies to bought-in stock as well as returning animals that were grazed in a different location or a shared area off-site.

If available, keep the new animals in an enclosed yard for the first 24-48 hours when they arrive. This window allows any anthelmintic treatments you administer time to work, and any parasite eggs shed in faeces will fall onto the yard instead of contaminating your pasture [1].

Perform a faecal egg count on the new animals. Understanding which worms are present on your farm and identifying any resistance to certain medications prevents unnecessary treatments in the long-term. Not only does this help combat anthelmintic resistance, it helps to ensure the best performance in your animals whilst keeping costs down [2].

Keep things clean. Any faeces passed onto the yard during the 48-hour holding period should be disposed of carefully and should not be spread onto areas intended for grazing.

Once your initial FEC has been performed, treat the new animals with an effective anthelmintic product, if necessary [1].


2. Choose the right anthelmintic

Deciding which anthelmintic to use is very important; the goal here is to remove as many resistant worms as possible. Some excellent guidelines have been produced to aid in treatment selection for cattle and sheep [3] [4] [5]. At present, there are 5 licensed groups of anthelmintics for sheep, and 3 for cattle. Multi-active products contain more than one active against the same target parasite, an example of which is Startect™ from the 5-Sl group which contains both derquantel and abamectin [6].


As widespread resistance has been reported in the older groups of anthelmintics, it should be assumed that resistant roundworms may be present in any new animal joining your stock [7]. Aim to use two broad-spectrum products with compatible actives to remove as many resistant parasites as possible. Incorporating the newer group 4 & 5 anthelmintics into quarantine protocols will help slow down the resistance to older drenches and keep them working for longer [8].

NOTE: To protect efficacy, the newer drenches should only be used for quarantine protocols or late-season dosing unless under the direct advice of your veterinarian.




Whilst reports of resistance are less common in cattle, resistance is still a significant concern and product choice requires careful planning.  As a high number of reports have been associated with group 3-ML products, consider using the remaining groups.



3. Dosing correctly

Every use of an anthelmintic product provides an opportunity for any worms present to develop resistance [10].  Careful administration of your chosen product is key to protecting the efficacy of the actives on the farm.


  • Adjust the dose weight to the heaviest animal in the group.  Before using equipment to begin weighing animals, make sure your scales have first been calibrated correctly. NOTE: If there is a large variance in the weight of individuals, it is best to divide these into sub-groups when calibrating the dose.  This is particularly important for sheep if using a product containing closantel, as overdose may lead to permanent blindness [11].
  • Regularly maintain any dose guns, ensuring they deliver the correct volume of drug with no large air bubbles.  The durability of the gun will depend on the material it is made from.  If there are any signs of damage, the gun should be replaced as per manufacturer’s instruction.
  • Ensure animals are restrained well for this procedure.  Excessive movement during application may lead to physical injury or failure to receive the correct volume of medication.
  • Anthelmintics of different groups must be administered separately using a different gun.  They must not be combined, or given with any other products to avoid compatibility issues between actives and accidental dosage alterations [12].
  • Always follow the manufacturer’s advice, checking regularly for any changes to storage recommendations, dosing procedure, or withdrawal periods.


4. Turning out

Once your animals have been tested and treated over the first 48 hours, they can be turned out to pasture but should not mix with your existing stock for a further 3 weeks.  

  • Choose a ‘dirty’ pasture grazed previously by home animals, as this will carry a population of eggs and worms already residing on site.  The intention behind this is to ensure any resistant worms still present after treatment are diluted by the resident ‘refugia’ worms without resistance to the product used [8].
  • Perform a faecal egg count reduction test (following manufacturer guidelines) on at least 10% of the group 10-14 days post-treatment.  This would identify if the anthelmintic product used has been effective.  If repeat faecal testing results are positive for eggs, it is important to discuss this with your veterinarian to investigate possible resistance issues or treatment failure.

NOTE: Resistant worm eggs may be shed onto pasture selected for turnout. It is important that the area chosen is not grazed by young or naïve animals until the grazing can be made safe, or has been used again by resident animals with high worm burdens [7].


5. Merge the groups!

Once the quarantine steps have been carried out, the new animals can be introduced to your existing groups with minimal risk of contaminating the pastures. 

  • Don’t forget to ensure the holding yard is thoroughly cleaned, with any faeces shed by the newcomers over the initial 48 hours disposed of safely away from pasture intended for future grazing.



  1. Beth Wells. Biosecurity for key livestock diseases [Internet]. Moredun Research Institute; 2016 [cited 2024 Mar 13]. Available from:
  2. SCOPS select the appropriate anthelmintic [Internet]. [cited 2024 Mar 14]. Available from:
  3. SCOPS | Sustainable Control of Parasites in Sheep [Internet]. [cited 2024 Mar 14]. Available from:
  4. Resources – COWS – Promoting Sustainable Control of Cattle Parasites [Internet]. [cited 2024 Mar 14]. Available from:
  5. Teagasc. Quarentine treatment – avoid buying in resistant worms [Internet]. [cited 2024 Mar 22]. Available from:
  6. SCOPS. Broad Spectrum Anthelmintics [Internet]. [cited 2024 Mar 22]. Available from:
  7. SCOPS quarentine procedures and treatments [Internet]. [cited 2024 Mar 15]. Available from:
  8. Group 4 and 5 Products | SCOPS [Internet]. [cited 2024 Mar 14]. Available from:
  9. COWS Control of worms sustainably [Internet]. [cited 2024 Mar 14]. Available from:
  10. War of the Worms | Moredun [Internet]. [cited 2024 Mar 13]. Available from:
  11. SCOPS urges care with dose rates when using products containing closantel | SCOPS News [Internet]. [cited 2024 Mar 13]. Available from:
  12. SCOPS administering anthelmintics effectively [Internet]. [cited 2024 Mar 13]. Available from:
  13. Mike Taylor. Implementing SCOPS quarantine treatment guidelines for sheep. vet times 2016; Available from:

Our Insights

Our insights look at how parasite control is handled within Ireland and how the agricultural industry has become dependent on medicating as a preventive measure.

We aim to combat medicating as a preventative measure and publish informative content to help farmers and vets medicate cattle in the future.