Internal parasites in cattle and sheep are one of the most persistent and costly challenges facing livestock producers. Whether you’re running sheep or cattle, worm burdens can quietly erode productivity through reduced growth rates, lower fertility, and compromised animal health, often without obvious early signs.
Traditionally, many producers have relied on routine drenching programs to manage worms. However, these programs are increasingly under pressure as drench resistance becomes more widespread across Australia. What once worked reliably is now delivering inconsistent results, making it harder to maintain control.
This is where DNA testing for parasite resistance in livestock is emerging as a powerful tool, allowing producers to shift from short-term fixes to more targeted, long-term genetic solutions for worm management. Specifically, using the WEC ASBV gives producers a repeatable, genetic basis for improving sheep worm control and reducing reliance on chemical treatments.
Parasite control in cattle and sheep starts with understanding just how much worm burdens can cost you. In livestock, internal parasites can lead to:
- Reduced weight gain and poor growth rates
- Anaemia, particularly from blood-feeding species
- Lower fleece quality and yield in sheep
- Reduced fertility and reproductive performance
- Increased susceptibility to other diseases
Even moderate parasite loads can limit productivity and profitability. By the time clinical signs appear, production losses have often already occurred.
This is why there is a strong case for proactive monitoring rather than reactive treatment. Waiting until animals show visible signs of parasitism means you are already behind, both in terms of animal welfare and economic performance.
How producers monitor worm burdens
Effective parasite control starts with understanding what is happening within your herd or flock. There are several tools available, each with its own strengths and limitations:
Faecal Egg Counts (FECs)
Faecal egg counts measure the number of worm eggs present in manure samples. They are widely used and relatively cost-effective, providing a useful indication of overall worm burden.
Limitations: FECs don’t identify worm species, rather they generally distinguish between major groups of worms, and may not always correlate perfectly with actual worm numbers or impact.
Larval culture
Larval culture involves incubating faecal samples to allow worm larvae to develop, enabling identification of parasite species.
Benefits: Provides species-level insight, which is critical for treatment decisions.
Limitations: Time-consuming (often taking 7–10 days) and requires specialised expertise.
Selection based on DNA Testing for parasite resistance in livestock
Worm Egg Count (WEC) is a moderately heritable trait, therefore selecting sheep with better worm resistance, using the WEC ASBV, can improve flock worm resistance. WEC ASBVs are genetic estimates that rank animals based on their ability to resist or suppress worm burdens.
Benefits: Provides a repeatable, heritable measure of parasite resistance that can be used for selection and breeding decisions.
Limitations: Not a real-time diagnostic tool, and must be used alongside monitoring tools like FECs.
How DNA testing supports long-term parasite control
Support treatment decisions
While WEC ASBVs do not replace diagnostics, they provide valuable context. Sheep flocks with lower average WEC ASBVs are generally more resilient to worm challenge, which can reduce the frequency and intensity of drenching required over time.
Better diagnostics to overcome drench resistance
Drench resistance is a growing issue, particularly in sheep enterprises. Continued reliance on chemical control alone increases selection pressure for resistant worms.
By incorporating WEC ASBVs into your breeding program, you can:
- Gradually reduce reliance on drenches
- Lower overall worm contamination on pasture
- Build a flock that is naturally more resilient under parasite pressure
Better genetics don’t eliminate the need for treatment, but they make every treatment more effective and less frequent.
Breeding for parasite resistance
Effective long-term sheep worm control depends on more than treatment alone. WEC ASBVs are one of the most practical tools available for breeding sheep with improved parasite resistance. Animals with lower (more negative) WEC ASBVs tend to carry fewer worms and shed fewer eggs onto pasture.
Over time, selecting for these traits can:
- Improve whole-flock resilience
- Reduce pasture contamination
- Enhance productivity under challenging conditions
Importantly, there are generally low and non-significant genetic correlations between WEC and other production traits. Therefore, incorporating WEC into a program as part of a well-rounded breeding objective will have little direct adverse impact on those production and reproduction traits (e.g. growth, fleece, fertility).
How Xytovet can help with your long-term parasite control strategy
At XytoVet, we support producers in building sustainable parasite control strategies that go beyond short-term treatments. Whether you’re focused on parasite control in cattle or improving sheep worm control across your flock, integrating WEC ASBVs with practical on-farm monitoring helps you:
- Interpret and apply WEC ASBVs in your breeding program
- Combine genetic selection with effective monitoring tools like FECs
- Reduce the long-term impact of drench resistance
- Improve productivity through more resilient livestock
In an environment where traditional worm control methods are under pressure, genetics offers a powerful path forward. WEC ASBVs are not a quick fix, but they are among the most effective tools available for long-term, sustainable parasite control.
Contact XytoVet today to discuss your long-term parasite control strategy.
