I have always fed Natural Balance "Duck and Potato", along with Wellness "New Zealand Venison and Sweet Potato".
Mine love the change, every so often, and have not had a problem. I stick with two protein sources, that's it, and
would not be a problem to eliminate one, or both.
I also give different treats (variety of fresh cooked veggies, as well as fresh fruit).
Like you, I cannot imagine eating the same thing, day in and day out. Although it "works", just seems unnatural to me.
With research, I believe you can certainly add a bit of variety to their diets. Just keep the two protein sources only.
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