Wairarapa finishing farm triple drench resistance case study

The aim of this study was to provide an understanding of introducing refugia into a lamb finishing operation that had a triple drench resistance issue. Refugia, introduced through lambs with susceptible parasites, was compared to the more conventional practice of quarantine drenching.


Resistance of parasites, or worms, to all classes of drench is a major concern in New Zealand farming systems. Intensive finishing and hogget grazing systems are at high risk of developing triple drench resistance, as are areas on farm predominately utilised for grazing young stock.

There is an opportunity to better understand drench resistance on farm. This project harnessed the power of relationships between a group of Wairarapa breeding and finishing properties, their vets and industry experts to have an in depth look at the impact lambs supplied from the group breeding properties had on a large scale finishing farm receiving their store lambs, including the development of triple drench resistance on this farm.

Key results

Know your worms. It is important to have a recent faecal egg count reduction test (FECRT) from the farm you are buying lambs from prior to arrival to your farm. By doing this, you know if you are introducing parasites that will be susceptible to drench and can introduce refugia on your farm, or drench resistant parasites that will increase the likelihood of drench resistance on your farm. In this study, the group of farmers shared their recent FECRT results and explored how their results impacted the next farm their stock traveled to. The project enabled them to reduce cost and gain efficiencies by cutting out ineffective quarantine drenches, improved the relationship between breeding and finishing farms and showed a start to reversing triple resistance status of the finishing farm involved.

Triple combination drenches may not be effective quarantine drenches. This includes for hogget grazing blocks and stock purchases. To know what quarantine drench you need, you need to know your worms.
For the introduction of refugia onto the farm the eggs must develop into infective larva, be ingested by lambs and breed. The time of the year to best achieve this and not induce clinical parasitism, or disease, needs to be considered for each farm system.

In this study, an increase in efficacy of drench was shown on the farm by both refugia and quarantine drench procedures. Testing will continue on this farm over the next 2 years to compare refugia and quarantine drench to determine if one or the other is better to reverse the effects of drench resistance over time.

Refugia can come with risks. In this study there was an unintended introduction of barber’s pole worm in the refugia trial. Barber’s pole was not detected at the initial screening but was detected in the refugia farm when tested 28 days later.

The results from this study so far suggest that both quarantine drenching and refugia can be used as management tools to reverse triple drench resistance. However, due to the short period of this project (6 months) testing will need to continue over the next 2 years to reliably confirm these results.

Benefit for farmers

This study demonstrated that by knowing the status of the parasites both on your farm and the farm you are buying stock from, you can put in place effective management strategies to reverse triple drench resistance.

Timeline and investment

This was a six-month study with investment by B+LNZ of $10,000 over the duration.


This project was carried out by Inside New Zealand Ltd, PGG Wrightson, South Wairarapa Vets and funded by B+LNZ and Silver Fern Farms.

Project leads: Renee Hogg (Inside New Zealand Ltd) and Andrew Dowling (PGG Wrightson).
Farmers involved: Wairarapa Producers Group.
B+LNZ point of contact: Will Halliday and Cara Brosnahan.