The menu at chef José Andrés’s Bazaar Meat in Las Vegas notes that its Vaca Vieja steak is made from a “hand-selected working cow.” The beef comes from a meat company called Mindful Meats, where, on the cow’s “final day,” employees “look each cow in the eye and say ‘thank you’ as they load onto the trailer,” its website explains.

Welcome to the final frontier in the discussion about transparency in food: meat. Consumers are demanding to know more about where their meat comes from, but food marketers say it’s more complicated...