beef of horse? Did you mean beef OR horse?
Okay, use logic. Dogs (and all mammals) take tens of thousands of years to change on a molecular level. I am not saying we couldn't breed dogs so they only thrive on ONE protein source, but we aren't there yet and would be insane to breed for it. I want to spit at companies that produce breed specific food.. what a scam.
YES there are special needs for breeds who have some disorders (such as copper toxicity), for giant or tiny breeds, for geriatrics and very active. Yep. But in general, unless your dog is allergic to a certain protein (and BEEF is the one most allergies form to, then chicken.. but they also get allergic to lamb and venison), any high quality protein (including horses) would be fine.
I had never heard of Red Moon so looked them up… they look interesting
http://www.redmoonpetfood.com/why-redmoon.html
But I suspect their cost is much more than the quality would justify for me… however if your dog likes it, looks good. I didn't find them on the dog food comparison chart but I will ask around.
http://www.doberdogs.com/menu.html