Raw Prime Meat is a rare food source in Ark. It is best to cook it before eating it (no steak tartare!). It is also used in taming and does become spoiled meat. Cooked Prime Meat lasts much longer than Raw Prime Meat. Watch out, as it spoils extremely fast. And Raw Prime Meat does not stack. You can lose it all in under two minutes if you can't cook it extremely fast. Cooked Prime Meat does stack, which dramatically increases the time you have before it spoils.
Raw Prime Meat comes from harvesting dead animals. But you won't find this quality of meat on just any Dino. For the most part you'll want to look for the big and dangerous Dinos. The T-Rex, Bronto, Stego, and Megalodon are good examples. Sound challenging? It is!
Remember, Raw Prime Meat does not stack and it spoils 2 minutes from harvesting. You need to cook it right away. If you don't have an industrial grill (high level cooking equipment) and you have more than one or two pieces of Raw Prime Meat, you'll need multiple campfires to cook it fast enough. This is because the campfire will only cook one piece of meat at a time.
Now the harvesting of animals once they are dead is rather interesting. In fact, for a premier survival game, it's quite weird, but there are no proper tools for this task. When you harvest an animal it seems to balance out like this: a Pick, metal is better than stone, may yield more meat and fewer hides, while using a Hatchet, again metal is better than stone, will tend to yield more hides and potentially less meat.