Written by Dr A. Liam Mowbray, Angus Australia — AngusPRO Magazine 2026
Internal parasites remain one of the most persistent productivity challenges facing beef graziers across New Zealand. While seasonal conditions vary, the impact of worms on growth and overall performance is consistent — and costly.
At Angus Australia, we are investing in research aimed at providing breeders another tool in the box: the ability to genetically improve resistance to internal parasites through Worm Egg Count (WEC) data.
Since 2023, Angus Australia has been collecting individual worm egg counts on our ASBP progeny during immune competence testing at weaning. To date, over 2000 individual phenotypes for WEC have been collected at weaning. Additionally, after treating the weaners with a single lifetime drench, we have followed a subset of animals through and re-tested them as yearlings. Interestingly, early results indicate that animals recording higher WECs at weaning often remain higher shedders when re-tested as yearlings, suggesting that parasite burden may have a repeatable biological and genetic component.
Why Worm Egg Counts Matter
Worm Egg Count is a measure of the number of parasite eggs present per gram of faeces. In simple terms, it provides an indicator of an animal’s parasite burden and its ability to regulate internal worm populations.
Animals that maintain lower worm egg counts under challenge are considered more resistant. Over time, selecting for this resistance may:
- Reduce reliance on chemical drenches
- Slow the development of drench resistance
- Improve growth rates under parasite pressure
- Support productivity in higher rainfall and coastal environments
Importantly, genetic resistance does not eliminate the need for good parasite management — but it can significantly strengthen it.
What Research Is Underway?
Angus Australia is actively building datasets that link Worm Egg Count phenotypes with genomic information.
This work involves:
- Collecting WEC records under natural parasite challenge
- Correcting for environmental and management effects
- Linking phenotypes to genotypes
- Investigating heritability and genetic correlations with economically important traits (eg growth and immune competence).
Preliminary analysis has also identified a favourable relationship between Worm Egg Count and immune competence at weaning, with animals displaying lower immune competence tending to record higher worm egg counts.
Why This Matters for Angus Breeders
For members operating in higher rainfall zones or regions with significant parasite pressure, genetic resistance could provide long-term cost savings and production stability.
This is particularly important as:
- Drench resistance continues to increase
- Chemical options become more limited
- Consumer and regulatory scrutiny around chemical use grows
A genetic approach may offer a permanent, cumulative and cost-effective addition to existing parasite management programs.
A Long-Term Investment
Developing robust breeding values requires large, high-quality datasets which takes time.
The work currently underway is about building the scientific foundations properly — ensuring that when tools are delivered to members, they are accurate, robust and commercially relevant.
This research represents a strategic investment in the resilience and profitability of Angus cattle across diverse Australian and New Zealand production systems.
We look forward to sharing further updates as analyses progress and datasets expand.
How can you get involved?
For further information or information on how to get involved please email liam.mowbray@angusaustralia.com.au.