Why not use this for dog food ingridient?

Legumes are

• More expensive
  
• Less widely produced (consistent supply would be a problem)
• Harder to mass process
• Rather high in protein so it would raise the protein levels of the food, which isn't necessarily a good thing since you'd have to lower the meat ingredients to keep it in balance
  

With that said, there's already a legume that's widely available and used in dog food - soy.  It's often used as a protein booster.  But I find soy to be harder for dogs to process than even any of the grains.  There's also food that use legumes, some as a main ingredient - ie, green peas.

No legume is really very easy to process, though some are worth the trouble for the dog - I just wouldn't want to offer a ration based on legumes. 

have you ever fed beans to a dog? you'll have to open your windows wide afterwards or perhaps invest in a gas mask. Dogs have even more trouble than people in digesting beans, and they are an incomplete poor quality source of protein. Many of the cheap "kill your dog slowly" foods are based on corn/soy instead of meat.

I feed beans (legumes) fairly regularly and this is no longer true for us.  It's just like anything else - they have to develop the wherewithal the digest them.  They aren't a regular part of the diet though, just an occaisional treat in stews and the like.  I use green peas, lentils, pintos, black beans, and kidneys.  I often use these because they provide "thickeners" that Ben can tolerate - so I can skip the egg, flour, and potato in a recipe.

Kord just recently went through a week of total raw since I did a food change that just didn't work for him. He was itching and scratching to beat the band, so I went total raw for a week before putting him back on his old kibble.

He was fed, everyday........(as opposed to his usual every other day)

Jack Mackeral, Salmon, Turkey, Beef, eggs (and shells), oatmeal, processed green beans, peas and cooked lentils and suppliments.

No gas, not one SBD, nothing.

Beans are sometimes used as a protein source in food-allergy elimination diets and for dogs who have other medical issues.

Very often the gas caused by eating beans is due to the beans not having been prepared (soaked and cooked) properly.  I sometimes include various kinds of beans in my dogs' home-prepared food, and they have no gas issues.

Canine Caviar uses "split pea" as the only carb source before the oil.