Cattle detained successful the pens of the Chihuahua Regional Livestock Union , astatine the Jeronimo-Santa Teresa borderline crossing successful Ciudad Juarez, Mexico connected November 27, 2024, aft the United States stopped imports of Mexican cattle owed to the beingness of screwworm.
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U.S. cattle ranchers volition soon person a caller mode to support their dwindling herds from the menace of the parasite screwworm, which is decimating cattle successful Mexico.
The U.S. Food and Drug Administration granted conditional approval for a cause called EXZOLT CATTLE-CA1, a topical attraction from Merck Animal Health for the prevention and attraction of New World Screwworm. It tin besides beryllium utilized arsenic a attraction and power for the cattle fever tick.
Farmers volition person entree to doses of the Merck cause starting connected December 20 done their veterinarian.
"The speech started successful July with the FDA, and due to the fact that determination is an constituent of quality nutrient safety, determination was a large information bundle we had to generate," said Holger Lehmann, vice president of pharmaceutical probe and improvement for Merck Animal Health. "This support is simply a important undertaking. The U.S. has received the product, and Mexico received it successful aboriginal November, wherever it is being used," Lehmann said.
The FDA has approved it with a 98-day withholding play to guarantee nary residue successful meat.
Lehmann cautioned that the cause unsocial cannot eradicate the parasite immoderate clip soon. "Experts archer america successful Mexico that they don't expect that they're going to beryllium capable to get escaped of the screwworm occupation quickly," Lehmann said. "They deliberation it's a multi-year occupation to get resolved."
On December 4, 2025, the U.S. Food and Drug Administration (FDA) granted conditional support to Exzolt Cattle-CA1, a fluralaner topical solution from Merck Animal Health, for the usage successful beef cattle.
Merck Animal Health
Screwworm is dispersed by hatching alert eggs successful the unfastened wounds of cattle, which provender connected their surviving tissue. Humans tin besides get infected. To support the U.S. cattle herd and to halt the dispersed of the parasitic fly, the U.S. Department of Agriculture has closed the borderline to Mexico for imports of unrecorded cattle, bison, and horses, connected and off, since 2024.
The borderline continues to beryllium closed.
Before the closure, Mexico was an exporter of calves to the U.S., with USDA information showing the U.S. imported over 1 million cattle annually, astir 3.3% of the U.S. full calf crop.
The screwworm outbreak successful Mexico is 1 of the reasons for volatility successful the cattle futures market, and down the high costs of beef, which has go a high-profile contented for the Trump medication among the president's falling canvass numbers connected the economy.
President Trump has blamed meat processors and U.S. cattlemen for the higher costs. Tariffs associated with carnal provender and farming instrumentality person been linked to the emergence successful beef prices, on with drought impacting herd size.
According to USDA data, arsenic of November 2025, the U.S. cattle connected provender were 11.7 cardinal head, down 2%, oregon 260,000 head, from 2024. That represents a U.S. cattle herd astatine its lowest level since 1951.
In November, Tyson Foods announced it was closing its large beef plant successful Lexington, Nebraska, and cutting backmost operations successful Amarillo, Texas, due to the fact that of the cattle shortage.
"As ranchers, we're gladsome to spot the FDA approving caller tools similar this," said sixth-generation Texas rancher James Clement III. "When we look fever ticks oregon screwworm outbreaks, having effectual medications and treatments connected manus isn't optional; it's essential," helium said. "These products springiness producers the quality to respond quickly, support our herds, and safeguard the broader livestock industry," helium said, though helium added ranchers volition person immoderate questions earlier they determination up with usage of the drug.
Because it's wintertime and the temperatures are cooler, Lehmann said the likelihood of flies carrying screwworm from Mexico into the U.S. is presently low. "But determination is hazard successful the spring, truthful we person capable merchandise disposable that we could deploy instantly to cattle ranchers for preventative action," Lehmann said. "Based connected what we know, this attraction is precise effectual against screwworm, and you privation to incorporate this. So payment attraction really becomes precise critical," Lehmann added.
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