Tackling rising drench resistance in livestock

Andrew Cribb

Drench resistance poses a growing challenge for vets and farmers, especially the alarming surge in triple drench resistance cases in recent years. This issue not only inflates costs due to the need for novel drenches, but also impacts animal performance significantly. When drenches fail, animals divert energy from growth to bolster their immune system — resulting in reduced weight gain.

How can one safeguard against triple drench resistance?

FECRT assessment

•     Regularly conduct a Faecal Egg Count Reduction Test (FECRT) to gauge each drench’s effectiveness against specific worm species on your farm.

Post-drench checks

•     Conduct a 10-day post-drench check on lambs at least twice yearly; absence of worm eggs after this period indicates successful drenching.

Have an effective quarantine protocol

•     Administer a novel drench (eg, Startect or Zolvix) with a BZ/Lev combination (eg, Corporal) for all new animals.

•     Perform FEC on these animals 10 days post-arrival.

Refugia policy implementation

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

Crop rotation consideration

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

Discussion and information sharing

•     Engage in discussions about drench resistance for shared knowledge and effective strategies.

Sales policy for lambs

•     Consider selling more lambs store to mitigate resistance risks. Managing a large number of lambs over an extended period increases the risk.

•     If you’re buying lambs in, try to source these from farmers with a good drench resistance status.

Increase your monitoring

•     Conduct FEC before ewe drenching to discern worm-related issues from feed-related ones.

•     Utilise larval cultures to identify worm species proportions for targeted treatment.

Ewe drenching review

•     Regularly reassess ewe drenching needs and focus on minimal drenching, implementing refugia policies.

Sheep-cattle ratio and pasture management

•     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 percent.

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

Addressing drench resistance challenges might feel overwhelming, but ignoring it worsens the problem. 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.