Cows stand in a feed barn at Hallstead Farms in Lexington, Ky., in February. Although the U.S. cattle herd size has shrunk in recent decades, U.S. beef production has remained strong, partly because cattle now weigh hundreds of pounds more than they did in the 1950s. Luke Sharrett for NPR hide caption toggle caption Luke Sharrett for NPR Grocery prices got you down? Learn how to cut your food bill with NPR's 4-part newsletter.  Sign up here  for budgeting tips, meal planning and more. Beef has long been an iconic and beloved staple of the American diet, from barbecue to hamburgers and steaks. Even as retail prices have soared recently, U.S. demand for beef has remained strong . Yet the U.S. cattle herd, including both beef and dairy cattle, is the smallest it has been in three-quarters of a century. Domestic producers had 86.2 million head of cattle on the first day of this year, according to U.S. Department of Agriculture (USDA) data , the lowest number since 1951 .…