Tackling Rising Drench Resistance in Livestock

Written by Bas van Luijk - Veterinarian, East Coast Farm Vets

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Drench resistance is an escalating challenge for vets and farmers, especially the alarming surge in triple drench resistance cases in recent years.

This issue not only increases costs due to the need for novel drenches but also significantly impacts animal performance.

When drenches fail, animals divert energy from growth to bolster their immune system, resulting in reduced weight gain.

How can you safeguard against triple drench resistance?

Regular faecal egg count (FEC) testing remains one of the most effective and cost-effective ways to monitor drench efficacy.

• Increase monitoring by conducting a 10-day post-drench check on lambs regularly. An absence of worm eggs after this period indicates successful drenching.

• Conduct FEC testing before drenching ewes to distinguish worm-related issues from feed-related ones.

• Utilise larval cultures to identify certain worm species, allowing for more targeted treatment.

• Drench strategically rather than routinely and regularly reassess ewe drenching needs. Identify high-risk periods and selectively treat only those animals that need it.

If previous on-farm testing has shown you have significant resistance, including combination resistance, consider conducting a Faecal Egg Count Reduction Test (FECRT) to evaluate each drench's effectiveness against specific worm species on your farm.

Effective pasture management plays a key role in mitigating drench resistance. Adopting a proactive stance is key:

• Use crop planting or grass renewal to disrupt the worm cycle and reduce reliance on drenches.

• Maintain a susceptible worm population by leaving a percentage of lambs un-drenched or allowing un-drenched ewes (preferably 2ths) to run with lambs.

• Maintain balanced sheep-cattle ratios to help prevent resistance development, as major sheep worms differ from those affecting cattle. Running a high number of one species can increase the risk of resistance developing by up to 80%.

• Implement effective pasture rotations to minimise larval contamination and maintain clean pastures.

Implementing an effective quarantine protocol will help prevent the introduction of multi-drench resistant worms onto your property. Administer a novel drench (eg. Startect or Zolvix) followed by a 10-day post-drench check to ensure its effectiveness.

Managing a large number of lambs over an extended period can increase the risk. Consider a solid sales policy allowing the sale of more store lambs to mitigate resistance. When purchasing lambs, source from farmers with a strong drench resistance status.

Addressing drench resistance challenges can feel overwhelming, but ignoring it will only makes the problem worse. Engage in discussions with industry experts, fellow farmers and vets to share knowledge and implement effective strategies.

Taking the initial step, such as talking to your vet team and conducting a post-drench egg count, is crucial in understanding your farm's situation and slowing down the development of drench resistance.

This article was published in the Gisborne Herald on 22/02/25.