I understand this post was made ~1 year ago, but seeing as you didn't get a response I thought I'd try to help you out: I've always been told easy keepers should only have a maximum ~30% alfalfa/legumes in their diet, the remainder should be grass hay/pasture [grass hays are timothy, coastal, teff, etc.]. If she's already a "chunky" horse, I don't really think you should be adding extra feed to her diet [the beet pulp / sweet COB you mentioned], you should instead be modifying what she's eating to get her to a more ideal weight. [Quarter Horses are supposed to be in the 950-1200 lbs range, so I'd use "1100 lbs" as a starting point for "Ideal Weight", and then adjust from there {basically, if she's still "too chunky" after treating her like a 1100lbs horse for several months, shift down towards 1000lbs; if she's getting too thin, shift up towards 1200lbs.}] I would personally switch her to grass hay in hay nets 24/7 if she's not on a grass pasture [allows for a constant slow "grazing" effect] plus a few flakes of alfalfa [with total hay intake weighed out to 1.5-2% of her ideal body weight = with the "1100lb" as your goal means between 16-22 lbs of hay per day], and add in a vitamin/mineral supplement [I use SmartPak's SmartEssentials for my herd; I also have Redmond Salt available for them in their stalls + run-in sheds at all times]. Depending on your horse's work level, I'd then consider adding 1-3 lbs of grain if she seems to start having trouble maintaining a more ideal weight [I start off with 100% whole oats. If my horse still has issues with weight maintenance I move on to either a 50:50 blend of whole oats + corn or an unsweetened COB mix. I don't really like sweet feeds, but if it's the only thing available in your area, then you can still try it.]

Jackie&Chip 12 that is false!