By Shelby Shank
Field Editor

The U.S. Food and Drug Administration (FDA) granted Merck Animal Health conditional approval of Exzolt Cattle-CA1, a topical pour-on solution for the prevention and treatment of New World screwworm (NWS) larval infestations. It is also conditionally approved for the treatment and control of cattle fever tick.

“This conditional approval gives cattle producers a new tool to combat two parasites threatening the well-being of cattle in the U.S.,” FDA Commissioner Marty Makary said. “Although NWS has not been detected in the U.S., cattle fever tick is here. This is the first drug conditionally approved by the FDA specifically for the control and treatment of cattle fever tick.”

The approval follows recent product market authorization in Mexico for Exzolt Cattle-CA1 to help prevent and treat NWS and control the spread of the parasite and protect livestock.

Merck Animal Health is prioritizing sending the product first to U.S. distribution partners located in areas along the U.S.-Mexico border that are more likely to have an immediate need by the end of the year.

“The threat of New World screwworm represents a growing concern to U.S. agriculture, potentially causing devastating economic losses for cattle producers that could reach hundreds of millions of dollars,” said Rick DeLuca, president of Merck Animal Health. “We worked closely with the FDA to accelerate availability so that veterinarians and cattle producers will have access to a powerful new tool to protect cattle from these serious parasites, helping to safeguard the industry’s economic future and the nation’s beef supply.”

FDA’s conditional approval is based on global studies demonstrating product safety and a reasonable expectation of effectiveness when applied according to label directions.

The product is approved for beef cattle two months of age and older and for replacement dairy heifers under 20 months. It is not approved for breeding bulls one year and older, dairy calves or veal calves.

A 98-day meat withdrawal period is required.

The treatment will be available by prescription only in 1-liter and 5-liter bottles beginning in the first quarter of 2026.