Recently, Blue Buffalo came clean and admitted by-product meal can be found in a "substantial and material" portion of its products, a year exactly after Purina filed a lawsuit claiming false advertising.
Purina originally conducted testing on Blue Buffalo back in 2014, when results showed the presence of poultry by-product meal in a number of Blue Buffalo's top selling foods. Blue Buffalo slammed other manufacturers for the use of the same ingredient in their products, but their CEO was quick to call the tests "voodoo science" assuring customers no such thing was in their "holistic" foods.
Now, although alarming because of the complete false advertising and lack of transparency to consumers, the fact is that poultry by-product meal is not the end of the world. (Gasp! We know. Double the false advertising.) Pets require nutrients, not ingredients. A diet full of great sounding ingredients can be less nutritious than a diet containing less appealing (to people) ingredients. With the ever evolving trend in human nutrition to find the penultimate diet or the eliminating the latest cancer/allergy/global warming causing food, savvy pet food manufacturers are banking on this health consciousness to market their products. This means perpetuating myths found in human diets, and applying them to the animal world. Case in point: the gluten craze.
The fact is veterinarians tend to recomment the larger companies like Hills, Purina, Royal Canin, etc. because they have huge research facitlities with multiple, sometimes hundreds, of veterinarians and veterinary nutritionists on staff. Their products are well researched and tested. On the other hand, companies like Merrick, Blue Buffalo, Frohm, etc. have maybe 1 veterinary professional, if that. They have fancy adverts that appeal to our more emotional side, but are not anything more than a fancy desrciption on the same food.
If you want the nitty gritty, as always, ASK YOUR VETERINARIAN! Four years of undergrad, followed by four years of vet school and potentially specialty training is always your most reliable option. There are a few other sources to check out, should you want to learn more about pet nutrition. Understanding Pet Food Labels, Dog Food Logic: Making Smart Decisions for Your Dog in an Age of Too Many Choices, and FAQ's on Pet Nutrition are all great resources for more in depth information.