The first and only pour-on product conditionally approved for New World screwworm prevention and treatment.

EXZOLT® CATTLE-CA1 (fluralaner topical solution) delivers a powerful new tool in the fight against New World screwworm. EXZOLT CATTLE-CA1 is conditionally approved by the FDA for:

• Prevention and treatment of infestations caused by New World screwworm (Cochliomyia hominivorax) larvae (myiasis)
• Treatment and control of cattle fever tick (Rhipicephalus microplus)

Fluralaner, the active ingredient, represents a breakthrough in parasite management as the first and only isoxazoline-class ectoparasiticide for use in U.S. beef cattle. With a novel mode of action and no known resistance, EXZOLT® CATTLE-CA1 delivers fast-acting protection in an easy-to-use pour-on formulation.

A new era in cattle parasite protection.

New World screwworm and cattle fever tick pose significant challenges for cattle herds. With parasites that are this relentless, old tools aren’t enough. The active ingredients in other conditionally approved NWS products have been used for decades for the treatment and control of gastrointestinal parasites. Only EXZOLT® CATTLE-CA1 brings a new active ingredient and drug class to the cattle industry, with no known resistance.

Watch the video and learn more about how EXZOLT® CATTLE-CA1 works to help cattle producers and veterinarians in the fight against these deadly parasites.

What you need to know about
EXZOLT® CATTLE-CA1.

WHAT IT IS
EXZOLT® CATTLE-CA1 is a broad-spectrum, long-acting pour-on containing fluralaner, a first-of-its-kind product and the first novel ectoparasiticide introduced for cattle in over 40 years.

WHAT IT DOES
EXZOLT® CATTLE-CA1 is conditionally approved for the prevention and treatment of infestations caused by New World screwworm (Cochliomyia hominivorax) larvae (myiasis) and the treatment and control of cattle fever tick (Rhipicephalus microplus).

HOW IT WORKS
EXZOLT® CATTLE-CA1 contains fluralaner, a novel active ingredient with a new mode of action and no known resistance, that acts systemically against infestations.

HOW TO USE IT
EXZOLT® CATTLE-CA1 is an easy-to-use pour-on formulation available by prescription only. It comes in two sizes: a 1 L bottle designed for direct topical application along the animal’s back, and a 5 L container for use with the EXZOLT® CATTLE-CA1 applicator. The blue-colored solution helps make dose measurement quick and accurate for each animal. Work with your veterinarian and follow all label directions.

WHY IT MATTERS
EXZOLT® CATTLE-CA1 delivers a powerful option to help protect cattle from emerging threats of damaging parasites like New World screwworm and cattle fever tick.

Innovative and proven parasite control for cattle.

EXZOLT® CATTLE-CA1 is a powerful new tool to protect cattle against deadly parasites. Fluralaner, the active ingredient, represents a breakthrough in parasite management as the first isoxazoline product for use in U.S. beef cattle.

With a novel mode of action and no known resistance, EXZOLT® CATTLE-CA1 delivers fast-acting and long-lasting protection. EXZOLT® CATTLE-CA1 received FDA conditional approval based on a reasonable expectation of effectiveness, supported by published studies and Merck Animal Health research. Fluralaner has demonstrated safety and efficacy across species in over 170 global clinical studies and is approved in 93 markets.

New World screwworm myiasis signs and symptoms.

Visible maggots (larvae) on animals in or around a wound. New World screwworm maggots have distinctive markings, such as bands of spines and a screw-like shape as they burrow into tissue.
Worsening wounds. New World screwworms burrow into living tissue, causing a wound of any size to get larger and deeper over time.
Unusual drainage. Blood or light-colored drainage may seep from the wound as tissue is damaged and destroyed.
Smell of decay. As New World screwworm feed and damage tissue, the wound often develops a strong, foul odor.
Signs of irritation. Cattle may display unusual head shaking, appear in pain or irritated, and may also bite or lick at the affected area.
Unusual flies. Adult screwworm flies are similar in size to a common housefly or can be slightly larger. They have orange eyes, a metallic blue or green body and three dark stripes along their backs

Photo credits: U.S. Department of Agriculture Animal and Plant Health Inspection Service

If you suspect NWS on your operation, reporting is required and helps stop the spread. Contact your veterinarian, state animal health official or APHIS immediately.

Cattle fever tick signs and symptoms.

Visible tick infestation, particularly on flanks, inner legs, along the belly and brisket.
Cattle fever ticks spread the disease babesiosis, commonly called cattle fever. Symptoms of babesiosis includes high fever, progressive anemia, jaundiced mucous membranes, dark red or brown urine, weakness, reduced appetite, rapid breathing, weight loss and neurologic signs

Photo credit: U.S. Department of Agriculture Animal and  Plant Health Inspection Service

On-Demand Webinar

Learn how to take action against New World screwworm using EXZOLT® CATTLE-CA1 with Dr. Deana Hardee

Dr. Deana Hardee, Merck Animal Health technical services veterinarian, shares insights on using this breakthrough treatment for New World screwworm in this on-demand webinar. She explains how EXZOLT® CATTLE-CA1 works, the research behind it, and when and how to use it for New World screwworm and cattle fever tick.

Watch the Webinar

More valuable resources

August 5, 2026

Chute side posters

These 17 x 22 in. posters explain what to look for and how to treat New World screwworm infestations. PDF downloads are available in both English and Spanish versions.

English poster Spanish poster

May 13, 2026

New World Screwworm in Cattle: Risks & Prevention

The New World screwworm parasite is a growing threat to U.S. cattle. Learn about the signs and ways you can prevent infestation.

July 17, 2026

Facing the Threat Together: Industry Aligns on New World Screwworm

The cattle industry has faced New World screwworm before—and won. The threat of this devastating parasite demands renewed vigilance, stronger coordination and a proactive mindset.

What is New World screwworm?

New World screwworm is a flesh-eating ectoparasite that poses a significant threat to livestock and wildlife in the United States. The adult NWS female flies lay eggs on an open wound of a living mammal. The fly larvae burrow into the flesh of the animal causing a serious, potentially deadly condition known as myiasis.

Why is it called New World screwworm?

In the larvae form, maggots burrow (screw) into tissue, like a screw being driven into wood.

How does New World screwworm spread?

New World screwworm primarily spread by movement of infested animals, both livestock and wildlife. Adult flies can travel short distances, typically less than 10 miles. To prevent spread, it is important to stay informed.

How to prevent New World screwworm?

Producers and veterinarians should increase observation of cattle and fly prevention practices. Schedule activities such as castration, dehorning, ear tagging and branding during low fly season when possible.

What does New World screwworm do to cattle?

New World screwworm is a flesh-eating ectoparasite that poses a significant threat to animal welfare. The adult New World screwworm female flies lay eggs at the edges of an open wound and larvae burrow into the flesh of the animal causing a serious, potentially deadly condition known as myiasis.

Where did the New World screwworm come from?

New World screwworm is native to the Western Hemisphere. It was successfully eradicated from the United States in 1966. There was an isolated outbreak in the Florida Keys in 2017. It has been moving north from Central America and Mexico and officially was found in the United States on June 3, 2026.

What does conditional approval mean?

EXZOLT® CATTLE-CA1 is conditionally approved by the FDA pending completion and approval of all efficacy data. It has a reasonable expectation of effectiveness in cattle based on published studies and Merck Animal Health research. Merck Animal Health worked closely with the FDA to accelerate access of the first-in-class ectoparasiticide to deliver a new, innovative tool to protect cattle and the beef industry.

Is Merck Animal Health taking steps for full approval?

Yes. Conditional approval lasts one year and can be renewed annually for up to five years. To renew, Merck Animal Health must show progress toward proving full effectiveness. The company is actively conducting research and submitting data to the FDA.

Can it be used off-label?

Off-label use is prohibited. It is a violation of Federal Law to use EXZOLT® CATTLE-CA1 other than as directed in the labeling.

What should I do if I suspect New World screwworm or cattle fever tick?

Contact your veterinarian immediately. Suspected cases must be reported to APHIS and state animal health officials. Visit www.aphis.usda.gov for reporting procedures.

What is fluralaner?

Fluralaner is the active ingredient in EXZOLT® CATTLE-CA1 and belongs to the isoxazoline class of parasiticides, representing the first isoxazoline ectoparasiticide conditionally approved for use in U.S. cattle.

Is there research on EXZOLT® CATTLE-CA1 in cattle?

Yes, three studies were conducted and used to obtain conditional approval. Two treatment studies showcased a single dose of EXZOLT® CATTLE-CA1 (2.5 mg/kg) delivered 100% prevention of New World screwworm infestations for 10–14 days after application. One treatment study showed 90.9% therapeutic anti-myiasis effectiveness by Day 2, and 100% efficacy by Day 3 with sustained protection through Day 5, with no myiasis observed.²

How do you administer EXZOLT® CATTLE-CA1?

Administer as a pour-on at 1 mL per 44 pounds of body weight, applied along the dorsal midline from withers to the base of the tailhead. Add 2.5 mL for each 110 pounds above 1,320 pounds of body weight. For the 1 L presentation, squeeze the product into the dosing chamber to measure total volume needed. For the 5 L presentation, use the provided dosing gun.

Body Weight (Pounds)	Dose Volume (mL)
220	5
330	7.5
440	10
550	12.5
660	15
770	17.5
880	20
990	22.5
1100	25
1320*	30

*Add 2.5 mL for each 110 pounds above 1320 pounds of body weight.

How does it work?

Fluralaner is administered through an easy-to-use pour-on formulation. It circulates in the bloodstream and targets the nervous systems of the labeled parasites, effectively killing them and protecting cattle from infestation.

When should EXZOLT® CATTLE-CA1 be administered?

Product use should be discussed with your veterinarian. This product is only available as a prescription for the prevention and treatment of infestations caused by New World screwworm (Cochliomyia hominivorax) larvae (myiasis) and treatment and control of cattle fever tick (Rhipicephalus microplus).

What precautions should be taken when administering to cattle?

Wear protective gloves, long sleeve shirts, pants and avoid skin and eye exposure during handling. This product can be flammable. Keep the product away from extreme heat or open flame, including branding irons.

What is the slaughter withdrawal period?

Cattle must not be slaughtered for human consumption within 98 days of treatment. If cattle are continuously exposed to temperatures at or above 60°F after product administration, then cattle may be slaughtered for human consumption 44 days after treatment. Violative residues may result if cattle are exposed to temperatures below 60°F after administration and are slaughtered at 44 days. For complete safety information and product dosing instructions, refer to the product label.

Can this product be given to lactating dairy cows?

EXZOLT® CATTLE-CA1 is not approved for use in female dairy cattle 20 months of age or older, including dry dairy cows; use in these cattle may cause drug residues in milk or calves born to these cows or heifers.

Will parasites develop resistance to EXZOLT® CATTLE-CA1?

As the first isoxazoline-class ectoparasiticide conditionally approved for U.S. cattle, EXZOLT® CATTLE-CA1 represents the first novel ectoparasiticide introduced in decades—offering a new chemical class with broad spectrum control to help address resistance challenges of other products. Implementing an integrated pest management approach to parasite control is essential to delay the development of resistance.

How should I store the product?

Store in original packaging at room temperature (59–86°F), away from sunlight, children and pets. After opening, use within 6 months.

Does it control horn flies?

EXZOLT® CATTLE-CA1 is only approved for treatment and control of cattle fever tick and treatment and prevention of New World screwworm myiasis.

Can it be used on wildlife, goats and sheep?

EXZOLT® CATTLE-CA1 is only approved for the use in cattle.

Does it control lice?

EXZOLT® CATTLE-CA1 is only approved for treatment and control of cattle fever tick and treatment and prevention of New World screwworm myiasis.

Can it be used on breeding bulls?

Not for use in bulls intended for breeding over 1 year of age, as reproductive safety has not been evaluated.

What special personal protective equipment (PPE) should be used when handling or applying the product?

Personal protective equipment should be worn, such as gloves, long sleeve shirt and pants, as well as glasses or goggles, while handling the product.

How quickly should I use the product after opening the container?

EXZOLT® CATTLE-CA1 should be used within 6 months after first opening.

Can it be given to calves younger than 2 months of age?

EXZOLT® CATTLE-CA1 is not approved for use in calves younger than 2 months of age.

Will it work for other ticks in the U.S.?

EXZOLT® CATTLE-CA1 is only approved for treatment and control of cattle fever tick and treatment and prevention of New World screwworm myiasis.

Important Safety Information

Conditionally approved by FDA pending a full demonstration of effectiveness under application number 141-617.
It is a violation of Federal law to use this product other than as directed in the labeling.
Not for use in humans. Keep out of reach of children. Accidental exposure may cause skin and eye irritation. Highly flammable. Keep away from heat, sparks, open flame or other sources of ignition. Use only for the prevention and treatment of infestations caused by New World screwworm (Cochliomyia hominivorax) larvae (myiasis) and treatment and control of cattle fever tick (Rhipicephalus microplus) in beef cattle 2 months of age and older and replacement dairy heifers less than 20 months of age. Not for use in bulls intended for breeding 1 year of age and older, dairy calves, and veal calves. Cattle must not be slaughtered for human consumption within 98 days of treatment. If cattle are continuously exposed to temperatures at or above 60°F after product administration, then cattle may be slaughtered for human consumption 44 days after treatment. Violative residues may result if cattle are exposed to temperatures below 60°F after administration and are slaughtered at 44 days. For complete safety information and product dosing instructions, refer to the product label.

U.S. Food and Drug Administration. 2025, December 4. Freedom of Information Summary: Exzolt™ Cattle‑CA1 (fluralaner topical solution); Application No. 141‑617. https://animaldrugsatfda.fda.gov/adafda/app/search/public/document/downloadFoi/17773
EXZOLT® CATTLE-CA1. Product label. Merck Animal Health; 2025.

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