WormBoss worm control program

Western Australia

Program Summary

The WormBoss worm control program for the Western Australian winter rainfall region has five components that are most effective when used in combination.

A summary of the components is below (click on the headings below for more information):

The South-West Medium to High Rainfall Zone

  • Lambs at weaning.
  • Weaners in early summer, after the pasture has dried off.
  • Hoggets (last year’s lambs) in early summer, as for the weaners.
  • Adult sheep in autumn, between the end of March and the end of April.

Low Rainfall Cereal Zone

  • Lambs at weaning or as lambs are moved onto a crop stubble if this is within a few weeks of weaning.
  • Hoggets (last year’s lambs) in early summer, unless WormTests over some years indicates there is rarely a need.
  • Drench all introduced sheep with a combination of no less than 4 unrelated drench actives with at least one of these being the newest drench actives: monepantel (Zolvix®) or derquantel (with abamectin—Startect®)2.
  • At other times, use the Drench Decision Guide and WormTest results to make drenching decisions.

2. WormTest at recommended times

The South-West Medium to High Rainfall Zone

  • Weaners, 4–6 weeks after their weaning drench, unless a summer drench is to be given at about that time.
  • Hoggets (last year’s lambs).
    • 6 weeks after the season’s break, or by the end of June at latest, then 6-weekly until the end of spring
    • 6-weekly after any drench is given in winter or spring (unless a drench is to be given at about that time).
  • Late-lambing ewes (mid-June onwards) WormTest 3 weeks before lambing is due to commence.

Low Rainfall Cereal Zone

  • Adult sheep in late March to April.

And at other non-routine times as described in the Drench Decision Guide.

3. Use grazing management to create low worm-risk paddocks

  • Prepare winter/spring low worm-risk paddocks for lambing ewes, weaners and hoggets by preventing contamination with worm larvae in the 3 to 4 months before they are needed:
    • spell paddocks, graze with cattle, use for crops, hay or new pastures.
    • or (not in coastal areas) graze with sheep that have a tested low worm egg count (less than 200 epg).
  • Choose the least contaminated lambing paddocks for the most susceptible lambing ewes (maidens, twin-bearing, or poorer condition).

4. Breed and feed for worm-resistant sheep

  • Use rams with better than average WEC and DAG ASBVs3 (choose the more negative values).
  • Maintain good nutrition to enhance the sheep’s immunity to worms.

5. Manage drench resistance

  • Avoid summer drenches to adult sheep (instead, drench in autumn).
  • Conduct DrenchTests each 2–3 years and use DrenchCheck-Day10s in between.
  • Avoid unnecessary drenching.
  • Use effective drenches only, and multi-active2 combinations where possible (those shown to be highly effective on your property).
  • Restrict the use of long-acting products to high worm-risk periods, and seek expert advice on their use. 
  • Rotate among all effective drench groupsfor each mob (and each paddock where possible).
  • Calibrate your drench guns, dose to the heaviest sheep and follow label instructions.

Drench refers to worm treatments regardless of route of administration.
2 Drench groups are the chemical family to which an ‘active’ belongs. An ‘active’ is the chemical in a drench responsible for killing worms. Some drenches contain more than one active and are called ‘multi-active’ or ‘combination’ drenches. See Drench groups and actives.
ASBVs=Australian Sheep Breeding Values.    

This is an up-to-date, integrated regional worm control program for sheep in the south-west region of Western Australia. It builds upon earlier programs and accumulated knowledge, including from the Department of Agriculture and Food, the experience of researchers, consultants and advisers, and new information from the ‘Integrated Parasite Management in Sheep’ project (funded by Australian Wool Innovation).

The program aims to improve the profitability and welfare of your sheep through:

  • fewer deaths and illness from worms
  • less drenching
  • improved productivity
  • prolonged life of drenches


Deborah Maxwell (Sheep CRC) and Brown Besier (DAFWA) .

The Sheep CRC wishes to acknowledge the contribution of the parasitologists, veterinary officers, extension officers, consultants and organizations that developed the original programs from which the WormBoss programs have been drawn, in particular, the Department of Agriculture and Food, Western Australia.

August 2012

Each regional ‘WormBoss worm control program’ has been developed from local research results and experience proven to be relevant and successful for most farms in the region. Sheep CRC acknowledge that this is not the only method of worm control in the region and more refined programs can be developed in consultation with your worm management advisor/veterinarian using information and knowledge specific to your property and sheep.

Future events cannot reliably be predicted accurately. Sheep CRC makes no statement, representations or warranties about the accuracy or completeness of, and you should not rely on any information relating to the ‘WormBoss worm control program’ (‘Information’). The Sheep CRC disclaims all responsibility for the Information and all liability (including without limitation liability and negligence) for all expenses, costs, losses and damages you may incur as a result of the Information being inaccurate or incomplete in any way for any reason.

No part of this publication is to be reproduced without the permission of Sheep CRC Ltd.

© Sheep CRC Ltd 2012 (ABN: 12 125 726 847)