Internal parasites are one of those hidden problems that every beef producer has to deal with. You might not always see them, but they’re constantly working behind the scenes—dragging down productivity, health, and profits. These parasites increase maintenance energy requirements, mess with nutrient absorption, and keep the immune system working overtime. All of that adds up to lost performance.
It’s easy to underestimate just how much internal parasites can cost you. But here’s the exciting part—if you run a 100-cow operation, you could be losing over $10,000 a year just from the effects of parasites. That’s not pocket change. The good news? Research shows that effective deworming programs can bump up weaning weights by over 30 pounds and improve pregnancy rates by more than 10%. That kind of gain adds up fast and goes straight to your bottom line, boosting your herd’s profitability and your optimism about the future.
But it’s not just about grabbing any dewormer off the shelf and calling it good. Timing and strategy are everything. Using the right product at the right time makes all the difference—and helps prevent parasite resistance from building up in your herd.
So, when you’re planning your deworming program, think about more than just convenience. Consider the parasites most active in your area, when your cattle are most susceptible, and whether your current treatment remains effective. A little extra planning can go a long way in keeping your herd healthier and your operation more profitable.
Sneaky but Serious: How Parasites Hurt Your Herd
The total effect that internal parasites can have depends on several factors. Factors such as age and stress levels also play a role in the development of infection. Calves are more likely to have them than mature cows, and cows will typically develop a decent immunity to them by around four years of age.
Internal parasites pose a significant threat to the health and productivity of cattle. Beyond the obvious health problems, they can lead to a severe drain on productivity. The most important impact is the decrease in voluntary feed intake, which responds to changes in the abomasum. This reduced intake hampers the absorption and digestion of essential nutrients, resulting in economic losses estimated to exceed $3 billion annually in the livestock industry. This alarming figure should serve as a wake-up call for beef producers to prioritize parasite control.
Though there can be others, four parasites are typically the most common. These include hairworms, Lungworms, Liver flukes, and Coccidia. Each of these parasites has a unique life cycle, specific symptoms to look out for, and different treatment options. Understanding the life cycle of these parasites is crucial for adequate control. I reviewed the various symptoms and treatment options of these parasites in a previous post, “Four common cattle internal parasites.”
From Grass to Gut: How Cattle Pick Up Parasites
If you really want to get ahead of internal parasites, you’ve got to understand how they live and spread. Knowing their life cycle is a game-changer when it comes to controlling them effectively, empowering you with the knowledge to make informed decisions about your herd’s health.
Most of these pesky parasites are picked up right out in the pasture. Here’s how it works: parasite eggs are shed in manure, which ends up on the grass. Then, while grazing, cattle accidentally eat the eggs. Once inside, those eggs hatch, and the larvae make their way into the intestinal tract or abomasum. That’s where they start causing damage—and laying more eggs, which are then passed back into
the environment through manure. And the cycle starts all over again.
The problem? These eggs and larvae are tough. They can survive harsh weather, including extreme heat and cold, which makes breaking the cycle tricky if you’re not intentional about it.
Here’s a quick breakdown of the cycle:
- Eggs are shed in manure onto pasture.
- Cattle eat contaminated grass.
- Larvae develop inside the animal, causing health and performance issues.
- More eggs are laid and passed through manure.
- Eggs survive on pasture, ready to infect the next grazer.
Understanding the cycle is why timing deworming and rotating pastures is so crucial. If you hit parasites at the right point in the cycle, you can make a big dent in their numbers—and protect your herd’s health.
For a more in-depth look, Kansas State’s guide, “Understanding Internal Parasites in Beef Cattle,” is a valuable resource. The more you know about how these parasites operate, the better you can stay ahead of them.
Which Dewormer Is Right for the Job?
While there are many options when it comes to choosing a product, the decision you make depends on several key factors. One important consideration is the product you used last time. Using the same product all the time can cause resistance to it. Resistance is when the parasites become less affected by the dewormer, thus making it ineffective. This resistance is why it’s crucial to rotate the active ingredients in your deworming program.
Although there are many different brands at your local feed store, they typically fall into three categories based on active ingredients. Benzimidazole, macrocyclic lactones, and imidazothiazoles are the three different types of dewormers. Each type has its own advantages and disadvantages. For instance, macrocyclic lactones are effective against a wide range of parasites. They can be administered in different ways, but they are more expensive. On the other hand, Benzimidazoles are more affordable but may not be as effective against all parasites. Understanding these differences can help you choose the right dewormer for your herd.
- Benzimidazoles: found under the drug names fenbendazole, oxfendazole, and albendazole. The commercial names for them are Safe-Guard, Panacur, Synanthic, aValbazen, Bimectin, and Noromectin.
- Macrocyclic Lactones are found under the drug names eprinomectin, doramectin, ivermectin, and moxidectin. Their commercial names are Eprinex, Eprizero, Ivermectin, Ivomec, LongRange, Dectomax, and Cydectin.
- Imidazothiazoles are found under the drug name levamisole. LevaMed and Prohibit are commercial names.
Timing Matters More Than You Think
For most producers, deworming typically occurs when cattle are already being handled, such as during branding, dehorning, or preg-checking. It’s convenient, sure. But if that’s the only reason you’re choosing when to deworm, you might be missing the mark. Timing matters, and doing it at the wrong point in the parasite’s life cycle can actually exacerbate the problem by promoting resistance. By being attentive to the timing of deworming, you can adopt a responsible approach to managing your herd’s health.
To really know if your dewormer is working, you need more than just a guess. That’s where the Fecal Egg Count Reduction Test (FECRT) comes in. It’s the best tool we have to measure the effectiveness of your treatment.
Here’s how it works:
- Collect manure samples before deworming.
- Deworm your cattle.
- Collect manure again 10–14 days later.
- Compare the egg counts.
If your dewormer is working effectively, you should see a reduction of 90% or greater in egg count. Anything less could mean that parasites are developing resistance—or that the timing, dosage, or product choice needs improvement.
If the results show your program isn’t hitting the mark, don’t panic. There are several things you can do to get back on track:
- Only treat high-risk animals, such as calves and yearlings.
- Avoid calendar deworming—base it on actual need.
- Try selective non-treatment by skipping the top-performing animals.
- Use combination treatments (two different drug classes).
- Always dose by accurate weight to avoid under-dosing.
- Review your grazing practices to reduce pasture contamination.
Making small, informed changes can significantly impact the health of your herd and ensure the long-term effectiveness of your dewormers.
Smarter Deworming Strategies That Work
📌 Target high-risk animals will include younger cattle, those less than 16 months old, and calves.
📌 Skip the calendar — Do not deworm by the calendar: Cattle should only be dewormed when they need it. An easy way to determine the parasite load of a herd of cattle is to count fecal eggs together.
📌 Selective treatment — To implement this strategy, producers should deworm all animals in high-risk groups, except for the top 10-15% heaviest or best-performing animals.
📌 Use combination treatments — This strategy involves treatments simultaneously with at least two drugs in different classes. An example of this is the use of one benzimidazole and one macrocyclic lactone. Using this approach, parasites resistant to one type will likely be susceptible to the other. This susceptibility would significantly reduce the selection pressure for resistance to either of the drugs.
📌 Avoid under-dosing — This typically occurs when animals are not weighed before treatment, resulting in a lower dose than is required for maximum effect. Under-dosing is a severe problem that contributes to the selection of resistance.
📌 Manage pastures wisely —Overstocking and overgrazing force animals to graze closer to manure piles, increasing the risk of parasite exposure. Using rotational grazing and giving pastures enough rest can help break the parasite life cycle and reduce exposure.
Make Your Dewormer Work Harder
A good internal parasite control program takes more than just grabbing a dewormer off the shelf and calling it a day. To really protect your herd—and your bottom line—you’ve got to think about when you treat, how you treat, and what you’re treating with.
One of the biggest mistakes producers make is sticking with the same dewormer year after year. That might seem like the easy route, but it’s a fast track to resistance. Parasites are survivors. Over time, the ones that aren’t killed off by a specific drug begin to multiply. Eventually, that whole parasite population becomes less affected by it.
This process isn’t about individual parasites becoming “immune”—it’s more like natural selection. Suppose you continue using the same active ingredient. In that case, you’ll eventually notice that it no longer works as well as it once did.
So what can you do? It comes down to rotating the active ingredient—not just the brand name. Many products on the shelf have different labels but use the exact same drug inside.
Here’s a quick checklist to help:
- ✅ Check the active ingredient listed on the label.
- 🔁 Rotate between drug classes (like benzimidazoles, macrocyclic lactones, and imidazothiazoles).
- 📆 Avoid treating on autopilot—base treatment on testing and parasite risk.
- 🧪 Use a fecal egg count test to monitor resistance and effectiveness.
By mixing things up and staying informed, you’ll help keep your dewormers working longer and your herd in better shape year after year.
