Worms Without Borders

Adaptability of parasitic worms makes a proactive deworming protocol a top priority for grazing beef cattle

DULUTH, Ga. (April 11, 2023) — Worm parasites are showing greater adaptability to both geographic movement and weather conditions. As the transport of beef cattle across geographies becomes more commonplace, so, too, does the prevalence of worm parasites. “Cattle movement has helped worms move into geographies where they may not have been previously,” explained David Shirbroun, DVM, Boehringer Ingelheim.

In addition, some worm species utilize a mechanism called inhibition to survive unfavorable weather conditions. Even in northern climates where it was thought the cold winter months could break the worm cycle, some species like Ostertagia, known as the brown stomach worm, burrow into the stomach lining and become dormant.

“Once the weather starts to warm up and cattle are back on green grass, then those worms erupt again,” Dr. Shirbroun said. “Treating those animals is important to break the cycle. For cattle grazing more than one month, an extended-release dewormer is an ideal fit, as it provides up to 150 days of control.”

Building a deworming plan

Because of these variables, it’s never too early to talk with a veterinarian about a deworming protocol. Taking fecal egg counts is a good first step to assessing current infection levels. It’s also important to ask a veterinarian about any potential resistance concerns in your area.

“We’re starting to see issues with resistance in certain worms in some pockets geographically, but it’s not a widespread issue, so a local veterinarian would be aware of which products to recommend in those situations,” Dr. Shirbroun noted.

Bleaux Johnson, DVM, West River Veterinary Clinic in Hettinger, North Dakota, is proactive in managing resistance. “We make sure we’re rotating different dewormer classes,” he said. “Or we may use an extended-release dewormer on certain groups of cattle, maybe just the calves and younger cows, so part of the herd serves as refugia.” Refugia (in which a percentage of the herd is selectively not dewormed) is recognized as a key practice in delaying the onset of parasite resistance.

Aligning the protocol to your operation

Another factor to discuss with your veterinarian is your operation’s grazing plan. Cattle are most susceptible to picking up worms and internal parasites when they are on green grass. The longer they graze, the more likely they are to become infected with worms.

“We look at the type of operation—cow-calf, grazing yearlings, stocker—to determine risk factors for parasitic worms,” Dr. Johnson stressed. “Any animals that don’t graze on grass aren’t at risk for reinfection. Beef cattle that are grazed for longer periods of time are at higher risk because pastures can be continually reinfected with larvae.”

For operations that turn out cattle for several months, an extended-release dewormer might be the right tool to keep the herd free of parasitic infections.

“One thing producers might not realize is that the peak level of larvae in the pasture is reached toward the middle to end of summer, months after cattle have been turned out,” Dr. Shirbroun said. “With a traditional dewormer that lasts maybe one month, the product has already worn off when we hit that peak infestation level, so cattle will be reinfected if they don’t receive another dose of dewormer. But with an extended-release product, parasites are controlled for up to 150 days after administration.”

There are three categories of deworming products:

Benzimidazoles (oral dewormers), which are effective on current infestations of adult and some juvenile parasites. “These are known as purge dewormers and offer no residual activity,” Dr. Shirbroun pointed out.

Imidazothiazoles are known for being quickly absorbed and distributed throughout the body but only control internal parasites. They can be delivered orally, topically and by injection.

Macrocyclic lactones (endectocides) are available in different formulations that control existing populations and provide different levels of residual activity:

Pour-on and injectable formulations typically provide residual activity of a few days to about 30 days.

An extended-release formulation can control parasite infections for up to 150 days, which is traditionally considered season-long control.

“Oral dewormers and pour-ons are great for feedlot cattle because those animals aren’t on grass and susceptible to reinfection. They’re also a good option for cattle grazing a short amount of time,” Dr. Shirbroun explained. “For cattle with a longer grazing period, an extended-release dewormer is ideal. You get up to 150 days versus the more traditional 30 days, so five times the control of a traditional dewormer.”

Dr. Johnson agreed, and added, “Producers benefit from the convenience of not having to re-treat the herd. Their herd is healthier, uses feed more efficiently, and gains weight better. As a result, we see less disease pressure, which means less antibiotic use.”

The science behind extended-release deworming

So, what makes an extended-release dewormer last all season long? Here’s how the technology works:

After the initial subcutaneous injection, the drug concentration reaches a high peak to control parasites right away.

Extended-release technology enables the remaining drug concentration to encapsulate into a gel matrix. This matrix continues to release the dewormer above therapeutic levels in the animal.

The matrix breaks down approximately 70 to 100 days after the initial treatment and releases a second peak. After 150 days, the drug is eliminated from the body.

“The vast majority of worm infections are subclinical, which means we’re not seeing outward signs of infection, but they’re robbing cattle of performance,” Dr. Shirbroun said. “Extended-release technology is a proven investment.1 It can help animals grow better by decreasing the parasite strain on their system.

“If you can control parasites, cattle can put on weight faster, keep their immune system stronger, and develop more efficiently. If you’re developing heifers for breeding purposes, they can potentially be bred earlier and have higher conception rates, which means they’re likely to stay in the cow herd longer,” he concluded.