Rethink parasite control in dairy youngstock (April 26)

Moving away from routine wormer treatments and taking a targeted evidence-based approach are key to parasite control and protecting anthelmintic efficacy. So what steps should producers take?

TEXT REBECCA DAWSON

Parasite control in dairy systems is entering a period of significant change. With no new anthelmintic actives expected in the near future and growing evidence of resistance on UK units, producers are being encouraged to move away from routine treatments and towards a more targeted evidence-based approach.

According to Boehringer Ingelheim’s Peter Howard, traditional worming strategies are no longer sustainable. “Our understanding of cattle parasites and how wormer resistance occurs has changed significantly in recent years. Typical approaches to worm control, such as timed treatments, using long-acting products, and blanket herd treatments are now understood to be problematic,” he explains.

Wormer resistance develops gradually, but its impact can be significant. Resistance is typically defined as a faecal egg count reduction of less than 95% following treatment. But Mr Howard says that production benefits can still be seen at lower levels of efficacy. “It’s not until efficacy reduces to 60% or 50% that a reduction in livestock productivity becomes evident, but by then the problem is more difficult to address.” This highlights the need for earlier intervention in management practices, rather than waiting until performance is visibly affected.

Sustainable control

The shift away from blanket treatments is being reinforced by growing field data. Rosevean Veterinary Practice’s Matthew Berriman says that sustainable parasite control in dairy youngstock relies on using treatments strategically rather than routinely. “Faecal egg counts are a valuable tool to help guide treatment decisions and allow producers to treat animals only when parasite burdens reach levels likely to affect health and performance,” he says. “This targeted approach helps ensure treatments are used when they will have the greatest benefit.”

He adds that recent work in practice has highlighted the growing challenge of wormer resistance. “Data collected in 2025 showed that around 50% of herds had some level of resistance to avermectin-type wormers. If parasite control continues to rely on frequent blanket treatments, resistance levels are likely to increase further, reducing the effectiveness of available products and potentially impacting growth rates in youngstock.”

Strategic treatment programmes based on monitoring can reduce unnecessary product use and often save both medicine costs and staff time. Most importantly, effective parasite control supports better growth in young animals, leading to improved fertility and productivity later in life. “Implementing this approach does not have to be complicated,” he stresses. “With vet guidance, faecal sampling and treatment planning can be easily built into routine herd management. Working with the herd vet to design a farm-specific, sustainable parasite control plan helps to maintain long-term herd health while demonstrating responsible medicine use to the wider industry and consumers.”

Test sample: faecal egg counts support anthelmintic-use decisions

Close monitoring

Monitoring is central to this approach. Regular pooled FEC testing of calves and youngstock from turnout through to mid-summer provides valuable insight into how parasite challenge is developing on the unit.

Rather than treating at fixed intervals, producers can use FEC results alongside grazing history and performance data to inform decisions on interventions. This allows treatments or other management steps to be timed to when animals have a rising parasite burden, but before high numbers of eggs are shed onto pasture.

Importantly, FEC testing also supports more selective treatment strategies. The well-established 80:20 principle suggests that around 20% of animals carry 80% of the worm burden. Identifying and treating these individuals, while leaving healthier animals untreated, can help maintain productivity without increasing selection pressure for resistance.

Performance monitoring provides an additional layer of information to help select animals most in need of treatment. Cattle that are failing to meet growth targets, despite adequate nutrition, are more likely to be affected by parasite burdens. Regular weighing and general observation of condition can help identify these individuals early.

Youngstock immunity

Youngstock management is a critical component of sustainable parasite control. Early exposure to low levels of parasites is necessary for the development of immunity, particularly to gutworms.

Mr Howard explains that some traditional approaches may work against this process. “Treating youngstock with long-acting wormers early in the grazing season, and implementing whole group treatment, may impact on the ability of youngstock to develop immunity to performance-limiting parasites, such as gutworm species and lungworm.”

Allowing a degree of controlled exposure, while preventing heavy infection, helps build resilience in young animals. This reduces reliance on treatments later in life and supports more stable performance across the grazing season.

Pasture management also plays a key role in controlling parasite challenge and slowing the development of resistance. One important concept is refugia – the proportion of the parasite population not exposed to wormer treatments.

Maintaining refugia helps preserve genetic diversity within parasite populations, reducing the selection pressure for resistant strains. Practical steps include avoiding ‘dose and move’ strategies, where animals are treated and immediately moved onto clean pasture, because this can significantly reduce refugia levels.

Instead, keeping cattle on the same pasture for a period after treatment allows untreated parasite populations to persist. Similarly, leaving a proportion of healthy, well-performing animals untreated can contribute to maintaining refugia.

Grazing management can also be used to reduce parasite exposure. Moving youngstock onto lower-risk pasture later in the grazing season, such as fields recently cut for silage or hay, can help limit challenge during peak infection periods.

Practical shift

While the move towards monitoring-based parasite control represents a change in mindset, both Mr Howard and Mr Berriman say that it is achievable in practice.

“The start of the grazing season is the ideal time to put a new worming strategy into action,” adds Mr Howard.

“By working with the herd vet and integrating FEC testing, performance monitoring and grazing management into routine herd management, producers can take a more informed approach to parasite control. This not only helps protect the effectiveness of existing treatments but also supports better growth, health and long-term productivity in dairy youngstock.”

As resistance pressures continue to increase, adopting these strategies will be essential to maintaining both herd performance and the sustainability of parasite control on UK dairy units.