Monitor for drench resistance

Monitor for drench resistance
By Tom David, Veterinarian, Anexa Vets Raglan

The resistance of worms to drenches is now commonplace on farms in New Zealand. Reduction tests performed through Anexa have found both double and triple resistance.
The main cost of drench resistance is decreased weight gains in young stock. A lot of money is spent every year on drenches that may not be earning their keep.

Drench check’s and Fecal egg count reduction tests are the two main ways we can assess drench efficacy on your farm.

1. Drench check

A drench check is a relatively quick and inexpensive way to screen for drench resistance in worms.
A faecal egg count is performed on a group of animals 7-12 days after drenching. There should not be worm eggs in faeces this soon after using an effective drench.
This indicates something needs to be changed, or further testing is required.

2. Faecal Egg Count Reduction Test (FECRT/ reduction test):

A faecal egg count reduction test provides additional layers of information compared to a drench check. A FECRT tells you which worms are resistant to which drenches on your farm, and to what extent. They can also be used to detect emerging drench issues.

Reduction tests are the best tool for identifying which products to use/avoid on your farm.
This extra level of detail does come with extra time investment, and cost.

If you are considering performing a FECRT, please get hold of us. There is a bit of planning involved on our end and they need to be timed correctly.


How to collect samples for a drench check

Performing a drench check is a quick and easy way to screen for worm resistance on your farm. A drench check involves performing a faecal egg count on a mob of animals 7-12 days after drenching. 12-20 animals should be sampled.
  1. Collect everything you need, read through the instructions.
  2. Run the mob into the yards, 7-12 days after drenching.
  3. Wait 5 - 15 mins until some of the animals defecate.
  4. Put on your disposable gloves and pick up fresh faecal samples. Samples should be soft and ideally still warm to touch. Each sample should be over 2 grams. This is around the size of half a kiwifruit. Bag each sample individually using ziplock sandwich bags or sample pottles.
  5. Collect and bag samples from 12-20 animals.
  6. Deliver the samples to the clinic as soon as possible. If this is not immediately after sampling, store them somewhere they won’t be affected by extreme heat or cool. Do not refrigerate.
For further information, sampling kits or if you would like our technicians to collect samples for you, contact your local Anexa clinic.

From Beef and Lamb NZ website:
Based on a farm finishing 3000 lambs annually.
Trial data – comparing lambs treated with a drench compromised by resistance, with lambs treated with a fully effective drench revealed:
  1. All the lambs looked fine. You could not pick the two groups apart.
  2. The production loss in the lambs treated with a compromised drench was 10-15% carcass value at the works.
See chart

It makes no sense to save 17c per lamb on a proper drench test every three years, when you could be losing at least $9 per lamb in carcass value.

The story is the same in cattle. That is, the cattle look great, yet the carcass yield shows their growth has been compromised.




Date Added: Wednesday, 4th November 2020


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