The American Meat Institute is striking back at reports that “meat glue,” a binding agent often used to patch together pieces of beef and other protein, is unsafe and unnatural. In an occasionally touchy conference call Thursday, the trade group said that the USDA considers such substances to be safe and requires its presence to be noted on retail labels. The product, however, isn’t always disclosed when it’s served at restaurants and other food service outlets, experts said. But using the binding substance to weave together high-quality cuts such as filet mignon with lower-priced meat such as chuck steak is...