Spotlight on endectocides: A practical tool for protecting cattle health and performance

Parasites can reduce weight gain, feed efficiency, reproduction and carcass value before problems become obvious. Endectocides can help control certain internal and external parasites with one systemic product class—but their value depends on identifying the parasite, choosing the appropriate formulation and using it at the right time as part of a broader control plan.

Today, producers and veterinarians are taking a closer look as they respond to familiar parasite pressure and emerging threats such as New World screwworm and Asian longhorned ticks.

What is an endectocide and what parasites does it control?

An endectocide is a systemic antiparasitic product with activity against both internal and external parasites. Many commonly used livestock endectocides belong to the macrocyclic lactone group, including ivermectin, doramectin, and eprinomectin, among others.

“Dectomax (doramectin) and ivermectin are true endectocides because they can control both internal and external parasites,” says Dr. Mike Catangui, entomologist and parasitologist manager for MWI Animal Health.

Products such as Exzolt (fluralaner) and Capstar (nitenpyram) are also systemic parasiticides, but they are not considered true endectocides because they act against external parasites and do not provide internal parasite activity.

How do parasites affect cattle performance and profitability?

Endectocides helped producers address internal and external parasites with one powerful product class, which is one reason they became such an important tool in livestock production.

“Endectocides or macrocyclic lactones were considered a breakthrough because they were able to control both internal and external parasites in livestock, companion animals and humans when they were first introduced commercially in 1981,” says Dr. Catangui.

Parasite pressure can affect:

• weight gain
• feed efficiency
• reproduction
• hide quality
• treatment labor
• follow-up handling
  
  

How have endectocides helped control cattle grubs?

The decline of cattle grubs, the larvae of warble flies, shows the impact of endectocides. Historically, cattle grubs damaged hides, connective tissue and muscle, reducing carcass quality and creating economic losses.

“Macrocyclic lactones have been credited for the dramatic decline in parasitism of U.S. cattle by cattle grubs,” says Dr. Catangui.

That history matters because Dr. Catangui sees a useful parallel with New World screwworm. “Both are the larvae or maggots of flies. Both feed on the live flesh of cattle. Both can be controlled with macrocyclic lactones or endectocides in the field,” he says.

The lesson is simple: parasite control works best before damage becomes expensive. Earlier planning, seasonal timing and accurate identification can help producers avoid chasing problems after performance has slipped.

Can endectocides help control New World screwworm?

The success of endectocides against cattle grubs raises an important question: Could the same product class have a role in managing New World screwworm?

Endectocides are not a replacement for New World screwworm surveillance, reporting, sterile-fly programs or veterinary intervention. However, researchers and veterinarians are considering whether macrocyclic lactones could have a supporting role in broader response strategies.

New World screwworm is a renewed concern because its larvae feed on living tissue. Screwworm flies are attracted to wounds and vulnerable areas, including the healing navels of newborn calves.

That caution is important. New World screwworm was eradicated from the United States roughly two decades before macrocyclic lactones became commercially available, so their role against New World screwworm is still emerging through modern field experience.

What can producers learn from the Asian longhorned tick?

The Asian longhorned tick underscores why parasite-control plans need to account for both established and emerging threats. First detected in the continental United States in 2017, this invasive tick has been associated with the spread of Theileria orientalis Ikeda, a protozoan parasite that can cause theileriosis in cattle. Clinical signs may include anemia, weakness, reproductive losses and mortality in affected animals. Because Asian longhorned ticks can reproduce without mating, populations can build quickly and become difficult to manage once established.

For producers, the takeaway is not to wait until a new parasite problem is widespread before reviewing control options. While endectocides are not currently labeled for hard-bodied tick control in U.S. cattle, Dr. Catangui sees Asian longhorned ticks as part of a broader discussion about how proven parasite-control tools may fit into future response strategies under veterinary guidance.

As with cattle grubs and New World screwworm, the opportunity is to pair accurate identification with timely treatment decisions, label compliance and an integrated plan that protects herd health and long-term product effectiveness.

What mistakes make parasite treatments less effective?

Emerging threats may be driving new interest, but day-to-day parasite pressure has not gone away. Lice, cattle grubs, mange mites, cattle scabies, horn flies and internal parasites remain part of livestock parasite management.

Common mistakes may include:

• Selecting a product before confirming the parasite
• Treating according to habit rather than current risk
• Assuming pour-on and injectable formulations perform the same way
• Choosing the product on hand instead of starting with the parasite
  
  

Stewardship is central to preserving the value of endectocides because the same tools producers rely on today need to remain effective for future seasons. “Overuse of endectocides can result in resistance development of the target internal and external parasites, resulting in reduced product efficacies,” Dr. Catangui says.

Resistance is not the only concern. Dr. Catangui also notes that non-target organisms, including dung beetles, can be affected and residues may persist in pasture ecosystems. Stewardship means using endectocides when they fit the problem, not simply because they are available.

Why this matters for producers

For many producers, endectocides are already familiar products. They may associate them with deworming programs, cattle grub control, or seasonal parasite management. What is changing is the context in which these products are being discussed.

New World screwworm and Asian longhorned ticks have renewed interest in tools producers may be able to implement while larger regulatory, surveillance and eradication efforts continue to evolve. That has brought endectocides back into the spotlight.

MWI carries endectocide products used throughout the livestock industry and can help producers think through how these tools fit into a broader parasite-management plan. The goal is not simply to recommend a product. It is to help customers make informed decisions about parasite identification, timing, formulation selection, stewardship, and veterinary collaboration.

Where do endectocides fit in a cattle parasite-control plan?

Endectocides earned their place in livestock production by bringing internal- and external-parasite control together in one systemic class of products. Effective use starts with identifying the parasite and confirming that the product, formulation, and timing fit the situation. Work with a veterinarian to protect current herd performance while preserving product effectiveness for future seasons. Endectocides may be part of the answer, but they should be used within an integrated program.