Originally Posted by After Shock Media

Um USDA prime, USDA prime+, and USDA prime- are all available at literally every farm in America. Do not let any restaurant jargon fool you. Those voluntery ratings just mean that the meat had 8.01% to 11%+ of intramuscular Fat and slightly abundant to abundant marbling. Nearly any distributor may obtain it and a large amount of the cattle raised for consumption are in this grade.
Now true fast food restaurants do not use prime typically, though less emphasis is placed on the chuck (the cut in & out uses) grading wise. Typically fast food places will use standard, comericial, select, or choice grades if they are not particular about the cut the ground beef is coming from. You are bound to find more comericial grade beef being used at places that use frozen patties. Places like Mcdonalds though have their own cattle so grading is generally not done.