FYI - my horses LOVE to eat raw chicken eggs. They have eaten them several times right out of the nests, shell and all. Do I purposely feed raw eggs to my horses? Heck NO! But they HAVE taken advantage of the opportunity when it's presented itself. I also had a mare eat a mouthful of horseshoe nails. (She was FINE, despite me having a heart failure.) I had a horse that loved hamburgers. The more pickles, mustard, and ketchup, the more she liked it! Is peppermint candy or carrots a natural food for a horse? NO. But people feed carrots and think it's a natural, healthy food. Heck, many horses have to be taught to eat apples as well. Alfalfa, beet pulp, oats, none of these are natural foods for a horse. Miscellaneous sticks, twigs, flowers, seed pods, prairie grass, roots, and even tree bark are natural foods for horses. Also, the average life span of a wild (correct term: feral) horse is about 10 years. Our domesticated pet horses live in excess of 20 to 30 years.
So do NOT kid yourself into thinking you are feeding your horse a "natural diet." You aren't.
Same arguments go for feeding a dog raw or BARF diets. The diet of a wild dog or dingo is carion derived mostly of small animals like rabbits and birds, or perhaps deer/antelope, et al, carcasses. Wild dogs eat bugs, trash discarded by humans, and and small amphibians. So feeding a horse a chunk of beef or a raw chicken breast is NOT natural. Not even remotely CLOSE to being natural! In fact, I have read studies indicating that a dog's digestive tract is not terribly effective at digesting beef or chicken protein. They are actually much more able to process duck or fish protein. And again, the lifespan of a wild dog is not typically 15 years or more. Lifespan is more like 2-6 years, max.
So all this "natural" bazooo is just that - bazooo as far as I'm concerned.
If given a chance, my dogs will lick up every last nugget of corn based chicken feed they can find! Dogs are opportunistic feeders that will eat everything they can get their teeth on.
My dogs eat Taste of the Wild, 6 star grain feed food, and I also cook nutritious meals for them made with human grade meats and cooked vegetables. But I don't think for one minute that this is a "natural" diet for them.
As for corn and soy for chickens, I don't buy soy so I don't know about that. Mine eat cracked corn as part of their "grain" mix (layer pellets, cracked corn, black oil sunflower). They get all sorts of fruits and vegetables and a little bread and oatmeal, yogurt, etc...
The natural diet for a chicken is grasses, bugs, worms, flowers, fruits or vegetables they might find, and even meat such as mice, small snakes, and each other if given half a chance!