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What is drench resistance testing?​

Our Drench Resistance Test is a Faecal Egg Count Reduction Test (FECRT) designed to evaluate and assess the anthelmintic-resistance status of identified internal parasites on a property to a chosen range of oral anthelmintics.

Currently it is only for use in evaluating resistance of gastro-intestinal roundworm parasites in sheep and calves.

How it works

Pre-treatment faecal egg counts (FECs) of 12 animals are compared against FECs 10-12 days post anthelmintic treatment to calculate the percentage faecal egg count reduction for each anthelmintic treatment.

Larval cultures are used to determine which parasite genera were present at the commencement of the FECRT, and which of those parasites are resistant to any of the anthelmintic treatments.

The optimal time to undertake the drench resistance test is in the spring or autumn when parasite levels are usually at their highest, and when most of the parasite genera are present.

The drench resistance test is best performed on young animals (less than 1 year of age) as their less developed immune systems are likely to result in higher and more varied parasite burdens.

Animals to be used in the test must have been present on the farm for a period of at least six weeks. 12 will be required per treatment group.

A composite (mob average) FEC for the test animals must be at least 500 eggd per gram (epg), although a FEC higher than 700 epg is desirable before the drench resistance test can be performed.

Sampling process

On Day 0 individual faecal samples are collected from 12 animals for each anthelmintic being tested. They are ear tagged with numbered tags, weighed and then accurately drenched (with a syringe) with the anthelmintic being tested.

  • Faecal samples are sent for individual egg counting and a pooled larval culture is performed to see what parasites are present in the animals.
  • On Day 10, individual faecal samples are again collected from all animals and sent away for egg counting and larval culture. 

A full drench resistance test report will be delivered by your Animal Health Area Manager, who will explain the results in detail and discuss management options.