US Halts Live Cattle Exports to Mexico After Screwworm Detected in Texas and New Mexico

The USDA emergency-suspended all live cattle exports to Mexico after screwworm cases appeared in Texas and New Mexico, freezing bilateral livestock trade in both directions.

The restriction, issued through the Animal and Plant Health Inspection Service (APHIS), went into effect immediately. It covers far more than slaughter cattle and breeding stock. The ban applies to equines, sheep, goats, wild ruminants, breeding pigs, and companion animals including dogs, ferrets, and commercial birds.

US laboratories have detected five positive screwworm cases so far. The latest cluster includes two in Texas: a cattle operation in La Salle County and an infected goat in Gillespie County. A third case appeared in a dog in New Mexico. The dog had originally been tracked by inspectors in Texas and had recently been in Mexico, which USDA investigators believe may have introduced the parasite into the region. Epidemiologists are mapping the transmission route.

The New World screwworm (Cochliomyia hominivorax) is a parasite that lays eggs in open wounds of warm-blooded animals. The larvae hatch and feed on living tissue. If untreated, infestations cause severe tissue destruction and death.

The USDA classifies screwworm as a reportable foreign animal disease. Any positive detection automatically activates suspension of live animal movements across state and international borders. The parasite was eradicated from the United States in the 1960s through a sterile insect technique program jointly run with Mexico and Central America. That program maintained a biological barrier in Panama to prevent reinfestation from South America. The current cases represent the first confirmed detections in US territory in decades, which is why the response has been immediate and sweeping.

This is not the first trade restriction tied to the outbreak. Mexico had already suspended imports of US beef earlier in the crisis. The new USDA export ban is effectively a reciprocal measure, but with a broader scope that blocks US producers from sending live animals south while the parasite remains active in American territory. The result is a two-way freeze on livestock trade across the border.

For the beef sector, this means US ranchers cannot ship feeder cattle to Mexican feedlots for finishing, a common practice in the integrated North American livestock market. Mexican slaughtering plants that process US-origin cattle face raw material shortages. The Grupo de Consultores de Mercados Agrícolas (GCMA) warned that immobilization of border shipments threatens regular supply at Mexican slaughterhouses. The group flagged potential price distortions across the national livestock chain if the disruption extends.

Mexican slaughterhouses depend on US feeder cattle to maintain processing volumes. A prolonged ban would force them to either reduce operations or find alternative supply sources, which is not straightforward in the short term given that US cattle have been a reliable input for decades.

Impact on US ranchers

Mexico is the top destination for US live cattle exports. Losing that market during a screwworm response period compounds stress on producers already facing tight margins and drought pressures across parts of Texas and the Southwest. The ban also disrupts seasonal movement patterns, where US cattle typically cross into Mexican feedlots for finishing before returning as boxed beef. That loop is now broken.

US cattle producers face a difficult choice: hold animals on feed longer than planned, incurring higher feed costs, or sell into a domestic market that may not have the same demand profile. Feeder cattle prices have already dipped in affected regions as the ban took effect, according to early market reports.

Trade resumption depends on risk assessments from the Mexican government and mutual control agreements between health agencies from both countries. Bilateral negotiations through diplomatic channels will define new cross-border exchange guidelines.

The USDA will need to demonstrate effective containment and eradication of the screwworm in the affected areas before Mexico lifts its import suspension. That means verifying that no new positive cases emerge after a defined surveillance period, and showing that control measures on affected premises are working. Mexico, in turn, will need to satisfy US animal health authorities that its border inspection protocols can detect and prevent re-entry of the parasite.

The sterile insect technique that eradicated screwworm from North America in the 20th century still exists. The US and Mexico jointly operate a production plant in Panama that produces sterilized flies for release. If the outbreak is contained quickly, that infrastructure could be reactivated. But if the parasite has established a foothold, the timeline stretches.

For now, both governments are in crisis response mode. The livestock industry on both sides is adjusting to a closed border with no clear reopening date. What started as a few positive lab samples has cascaded into a full shutdown of one of the most integrated agricultural supply chains in the hemisphere.