Worm Resistance and Resilience

Our flock is highly worm resistant, with each generation coming in at about -60% PWEC in Lambplan. In 2023 one of our rams jumped to -98% PWEC and we now have 17 out of the top 20 worm resistant rams in Lambplan. We are now the most worm resistant recorded flock in Australia.

Our stud sheep have not been drenched for the past four years and prior to this they were drenched only once a year at lamb marking. The past four years have been very challenging for worms in our district due to higher rainfall, green summers and dry autumns, with challenging feed conditions.

Ewes get their last drench at 1.5 years when their first lambs are weaned. Lambs are drenched as required after a WEC.

Our commercial ewes are drenched on an individual basis at marking, if they are under CS 3 (about 5-10% get drenched).

We lamb in Spring and run 12 sheep per ha on improved country and 6 per ha on leased country.

It has been a challenge getting WECs high enough to do individual WECs (needing over 400epg average). Twice in the past 6 years we have purchased worms from Resurrect Refugia and drenched lambs with worms. This has allowed us to get fast and accurate worm info, while also introducing chemically naive worms. With our low drench requirements these worms have taken over our original worm population making all chemical drench groups effective again.

Change in chemical effectiveness:

Results 2020 2023
White BZ 72% 96%
Abamectin 86% 99%
Levamisole 88% 100%

Worm resistance is driven by a more responsive or aggressive immune system. Other research has connected high worm resistance to better footrot resistance and a better response to vaccinations.

We also select for growth – animals that can grow under a worm load clearly have resilience. This massively reduces the risks to animal health and production loss due to worms in our high rainfall environment. Also reducing labour and chemical costs needed to manage worms.

Do you need to drench your mature ewes?

See below timeline showing how our ewes have managed their worms over the last 6 years, going from one drench per year at lamb marking to no drench at all.