This varied quite a bit from place to place and had a great deal to do with what food sources were available, and what role dogs played in society in the first place. My comment concerns the Chukchi, a nomadic people in Northeastern Siberia. These people bred the Siberian Husky, a medium sized but fierce dog, retaining many wolf-like characteristics such as howling and a very active prey drive, while nonetheless being quite tame such that incidence of them attacking humans was very rare. Huskies were mainly used for reindeer herding and pulling sleighs. Wolves were additionally used as hunting animals, though being far less tempered were more dangerous.

Northeastern Siberia is rather barren of edible plant life, so most of the Chukchi diet and lifestyle were based on the hunting and consumption of animals, particularly emphasizing seals and reindeer. Wolves and dogs being natural carnivores, it only made sense that Huskies would also have extremely meat-based diets heavy in reindeer and seal. Additionally, the trade of animal furs was prominent even before contact with the Russians, and exploded across the region with increasing Russian trade. These fur animals, including foxes, squirrels, and reindeer fawns, were viewed as much poorer-tasting than mature Reindeer or Seal by the Chukchi, and so after being skinned the carcasses would often be given to dogs.

Dogs have more acidic stomach acid than humans, and can thus better handle meat which has started to decay (though food poisoning is still a possibility). Decaying meat being unappetizing anyway, it was very frequently used as dog food for both huskies and wolves. The Maritime Chukchi—who live on the coast and have a less reindeer dependent lifestyle, would also prepare fish soups with moss for their dogs. Dogs would also eat animal bones, a good source of calcium. Veterinarians today generally advise against this as sharp bones can harm the digestive tract of dogs, but with no alternatives at the time this was necessary for dogs to get an adequate calcium intake.

Reindeer meat is quite nutritious to both humans and dogs, having large quantities of protein, iron, potassium, riboflavin, zinc, and vitamin B. Raw reindeer meat additionally has Vitamin C, and so raw meat was crucial to prevent scurvy for humans and dogs alike. Both meats are quite lean, and so both seal and reindeer blubber were consumed to provide very large amounts of fatty calories. Blubber would usually be given raw to dogs, while it would be processed into oil and used in soups or other dishes for human consumption. Because blubber was valuable as lantern fuel and critical to survival in times of famine, it would normally only be given to dogs when it was most plentiful.

I’m not as familiar with the feeding of dogs in cultures outside of the Arctic Circle so I can’t offer specifics, though in general these were still much more meat based than their modern diets, in contrast to the largely vegetable based dog foods used today. This was especially true in regions like Central Asia and Europe where dogs were primarily used for hunting.