Just for clarification: Does Walmart sell an Insulin approved for human use? Animal insulin has been used for human use, and human insulin for use in pets...
Insulin's amino acid sequence varies a little by species, but as far as I recall most mammal's insulins are interchangeable.
Novolin N is human insulin. Walmart pharmacies likely sell more than one brand/type, this was just the one my vet prescribed (although a formal prescription isn't necessary, you just have to ask the pharmacist for it). It was about $25, so I assumed it was the same stuff the parent comment was talking about.
Insulin's amino acid sequence varies a little by species, but as far as I recall most mammal's insulins are interchangeable.