With the US cattle herd already at a multi-decade low, the closure could further elevate record-high beef prices by keeping more calves out of the US cattle supply. Screwworms were eradicated from the US in the 1960s when researchers began releasing massive numbers of sterilized male screwworm flies who mate with wild female screwworms to produce infertile eggs. The import suspension will likely contribute to rising beef prices by tightening the supply of beef cattle, which dwindled after drought forced ranchers to slash herds. US beef prices likely also got a boost from a separate import suspension from Mexico over screwworms that lasted from November to February, experts said, and upward pressure on prices should persist through summer grilling season. Mexican cattle are usually fed and fattened on US farms for five to six months before slaughter, and a diminished slaughter rate can elevate beef prices.