For decades, parasite control in cattle has followed a familiar script: Treat the whole herd in the spring, treat again in the fall and trust that the job is done. It’s simple, efficient and deeply ingrained in how many operations function.
But that approach is starting to shift.
On the most recent episode of “The Bovine Vet Podcast,” Megan Bollin, a technical services veterinarian with Norbrook, and Nancy Jackson, a field veterinarian for the Mississippi Board of Animal Health, describe an industry moving away from routine, whole-herd deworming and toward a more strategic, data-driven approach.
At the center of that shift is a fundamental change in thinking. As Bollin explains, the goal is no longer the complete elimination of parasites but rather smarter management of them.
“Historically, we’ve had the mindset of just getting rid of all the parasites, right? One-hundred percent — we want them all gone. But we’ve got to consider that 90% of the life cycle is in the pasture. So we’ve got to learn to live with these parasites,” Bollin says.
Why Routine Deworming Falls Short
Routine deworming became standard for a reason. It aligned with when cattle were already being handled, minimized labor and offered a straightforward protocol producers could repeat year after year. The problem is that convenience doesn’t always align with biology. Treating cattle when they are easiest to handle may not coincide with the most effective point in the parasite life cycle, which ultimately limits the return on treatment.
“It may be a convenient time when we have them caught, and I know it takes a lot of labor and planning and resources to get those animals through the chute and treat them, but it may not be the most economically beneficial time to treat them if we’re not applying that product at the correct time in the life cycle,” Bollin says.
Because most of the parasite life cycle occurs on pasture rather than in the animal, poorly timed treatments can miss the window where they would have the greatest impact. The result is a system that feels consistent but may not be working as efficiently as intended.
Replacing Guesswork With Diagnostics
As parasite control becomes more strategic, diagnostics are moving from optional to essential. Instead of relying on assumptions or visible signs, producers are increasingly being encouraged to measure parasite burden directly.
Fecal egg count testing provides a snapshot of parasite burden by quantifying the number of parasite eggs present in a manure sample, giving a measurable baseline rather than relying on assumption. Building on that, the fecal egg count reduction test (FECRT) evaluates how well a dewormer is working by comparing egg counts before and after treatment — typically 10 to 14 days later — to determine the percentage reduction. A reduction of around 95% is generally considered indicative of effective treatment, while lower reductions may signal reduced efficacy or emerging resistance.
Together, these tools allow parasite control decisions to be based on data, helping tailor treatment strategies to the specific conditions of each herd rather than applying a one-size-fits-all approach.
“If you’re doing just a straight fecal egg count, it needs to be quantitative. A qualitative test — just saying whether parasites are there or not — is not helpful, because you’re always going to have parasites,” Bollin advises.
Those baseline measurements allow for informed decisions about whether treatment is needed and how well products are performing. Follow-up testing is just as important, helping confirm whether a dewormer is still effective.
Rather than relying on routine schedules, this approach acknowledges that treatment decisions vary from one operation to the next.
“There’s no magic number that says you need to treat at this high of an egg count,” Bollin says. “It’s going to depend on your geography, your herd and your operation.”
That variability is something producers already manage in other aspects of their operation. As Jackson notes, parasite control should be approached with the same level of flexibility.
“Every farm is unique — when they calve, when they wean — so it’s hard to make a cookie-cutter template,” Jackson says.
In many cases, the need for measurement comes down to what isn’t immediately visible. Subclinical parasite burdens can quietly reduce performance without obvious warning signs, making data even more valuable.
Refugia: A Counterintuitive but Critical Strategy
Rather than treating every animal, every time, the concept of refugia encourages leaving a portion of the parasite population unexposed to dewormers. Bollin explains that this approach helps preserve drug effectiveness by maintaining a population of parasites that remain susceptible, rather than selecting only for those that survive treatment.
“Refugia is leaving a percentage of the parasites unexposed to a dewormer. The idea is that resistance is a heritable trait, so we’re trying to dilute those resistance genes and maintain a population of parasites that are still susceptible to the products we have available,” Bollin says.
While it may seem counterintuitive, this strategy reflects a broader shift away from trying to eliminate parasites entirely and toward managing them in a way that sustains long-term control.
Implementing refugia doesn’t mean abandoning treatment. Instead, it means focusing on the animals that benefit most.
“We know that calves are going to be more susceptible, so ideally we want to treat those animals. But those mature cows — if they’re in good condition and have good nutrition — their immune system should be able to suppress those parasites,” Bollin says.
This kind of targeted approach allows producers to use dewormers more effectively while also supporting broader parasite management goals.
Combining Classes to Improve Efficacy
While refugia focuses on preserving a population of susceptible parasites, another strategy aims to improve how effectively treated parasites are eliminated. Combination deworming, or the concurrent administration of anthelmintics from different drug classes, is increasingly being used to improve efficacy in the face of variable parasite susceptibility.
Because these classes act through distinct mechanisms — such as macrocyclic lactones targeting parasite neuromuscular function and benzimidazoles disrupting microtubule formation — using them together can increase overall parasite kill and reduce the proportion of resistant survivors. The benefit becomes clear when considering how efficacy compounds across treatments.
“If you have 100 worms and you go in with a product that has 80% efficacy, you’re left with 20. Then you come in with a second dewormer, also at 80% efficacy, and it kills 80% of those 20. So you go from 80% efficacy up to 96% by using two products with different mechanisms of action,” Bollin explains.
This additive effect can help achieve the reduction typically associated with effective control, particularly on operations where single products no longer meet that threshold. Used alongside approaches like refugia and diagnostic-guided treatment, combination therapy becomes part of a broader strategy aimed at maintaining both short-term efficacy and long-term sustainability.
A More Strategic Future
Taken together, these changes represent a shift away from routine and toward precision parasite management. Instead of relying on fixed schedules, producers are being encouraged to align treatments with parasite biology, use diagnostics to guide decisions and adjust protocols over time.
That shift requires a willingness to rethink long-standing habits. As Jackson points out, progress often starts with being open to change: “We’ve always done it a certain way, but there’s always room to learn and adjust how we’re managing these parasites.”
It also depends on continued collaboration and learning across the industry. Parasite control is not a one-time decision but rather an ongoing process that evolves with new information.
“It’s continual education for both the producer and the veterinarian to understand the life cycle and apply that information to the herd,” Jackson says.
Ultimately, the goal is to move beyond routine and toward more intentional decision-making.
“I think very simply, it’s about not doing it on guesswork like we have been for decades; it’s about using the science and the tools that we have available and being more strategic about how and when we treat,” Bollin says.
Parasites are not going away, but the way they are managed is evolving. Producers who adapt to these new rules will be better positioned to protect both animal performance and the tools they rely on to sustain it.
To hear more from Bollin and Jackson on how deworming strategies are evolving, including where current protocols are falling short, listen to the full conversation on the latest episode of “The Bovine Vet Podcast.”
