Those terms "roughage products", "grain products", "grain by-products" are all why I don't buy these types of feeds.
These companies do, indeed guarantee the percentages of listed vitamins and minerals BUT, when they list things like "roughage, by-products", etc, that means they can use anything they darn well please, in that category, to get up to those guaranteed percentages.
They aren't lieing about the guaranteed percentages but those generic "ingredient" terms makes their formulas not fixed
I much prefer to buy from a company that is willing to list all their ingredients on the bag or on the tag. That might cost a little more money, when writing the check but, in the long term health of the horse, it might possibly save a vet bill.
There's a lady on another forum whose horse is so sensitive, she noticed a difference in his behavior, over a period of time, when buying one of these company's feed who does not have a fixed formula.
She even noticed a difference in the smell when she would open a bag. She was trying to find a place, within her driving distance, to buy some type of feed that has a fixed formula --- meaning they don't say "roughage" or "by-products".
I hope that made some sort of sense