dog food vs pet-food

dog food and pet-food both are nouns.

Word	Noun	Adjective	Verb	Adverb
dog food	Yes	No	No	No
pet-food	Yes	No	No	No

As nouns, pet-food is a hypernym of dog food; that is, pet-food is a word with a broader meaning than dog food:

Other hypernyms of dog food include pet food, petfood.

dog food (noun)	pet-food (noun)
food prepared for dogs	food prepared for animal pets