Drought conditions over winter may have compromised the condition of sheep and reduced their resistance to internal parasites. Short pastures and prolonged grazing close to the ground can increase the risk of worm larvae uptake.
Although pasture growth in spring typically lowers susceptibility, it remains essential to stay vigilant — particularly at and after weaning when young animals are most vulnerable.
Worm infection costs the Australian sheep industry an estimated $436 million per year in lost production. Sheep infected with worms exhibit signs such as weight loss, poor wool growth, scouring, and in severe cases, anaemia or death. The cost of worm infections can be substantial, with losses in growth, wool, and survival, along with treatment expenses.
Weaners are the most vulnerable group of animals, as they have the highest susceptibility to internal parasites. Their natural immunity, which protects them against worms, doesn’t develop until about 12-18 months of age. Stressors associated with the weaning process can also compromise immunity.
Conducting regular worm egg counts (WECs) provides the best chance of detecting a worm burden and targeting appropriate treatments. A WEC shows the number of worm eggs in a sample of faeces and indicates the size of an internal worm burden.
Regular monitoring through worm tests is crucial. These tests help determine when sheep exceed the WEC threshold, indicating the need for treatment.
Active monitoring also guides decisions on when not to drench, preventing unnecessary chemical use, saving the cost of treatment and reducing the risk of drench resistance.
The WEC at which you should drench varies based on the worm species and class of stock. Consult your private vet or refer to the Wormboss Drench Decision Guide once you have received your WEC results to decide whether a drench is required.
WEC kits can be provided by your veterinarian or laboratory and will include collection, storage, postage or drop-off instructions. For a mob WEC, 20-30 samples of fresh (warm) faeces should be collected.
Some animal health labs can perform a larval culture to identify the type of worms present so you can treat your flock with the most effective drench.
Top tips and tricks for effective drenching:
• Test for worms – essential to be regularly conducting with regular WECs. A list of ParaBoss WEC Quality Assured and approved labs is available on wormboss.com.au
• Use an effective product. The drench should kill 95 per cent or more of the worms, contain at least two active ingredients and be used at the recommended dose rate.
• Calculate the dose rate based on the heaviest animals in the mob. If there is a significant weight range, split the mob to avoid over or underdosing.
• Move sheep onto a clean paddock immediately after drenching, to maximise the benefits.
• Conduct a second WEC in 10-14 days after drenching, to check that the treatment has been effective.
• Continue to monitor your mobs for increases in WEC and treat as mobs reach thresholds. Careful monitoring can prevent avoidable adverse events and keep your stock thriving.
• Know the relative susceptibility of the different classes of livestock on your farm and the types of worms you normally see (a larval culture will determine this).
Worm management is not a set and forget process. It’s vital to be regularly monitoring flock health, WEC levels, and the effectiveness of management strategies. Be prepared to adjust the approach based on seasonal conditions, worm burdens, and sheep performance. Flexibility and responsiveness are key to successful worm control strategies.
Visit the Agriculture Victoria Feeding Livestock Website: Worms - monitor, measure and manage for information on WECs, and short videos on the impact of worms and management strategies.
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