Quite a while ago, Heather found an extruded pellet feed that she's got her whole herd on. Iron Ridge buys it in bulk, but it is also sold in bags, and it's cheap; about $10 for 50#. I switched to this feed when Poco was still here. They grew to love it after having been on it for the 8-10 weeks they spent at the farm when D was weaned. It's the only feed Daltrey's ever had.
Complete Assurance is manufactured by Bluebonnet Feeds in Ardmore, OK. Some big name breeder helped develop it, and it is available exclusively at one little feed store in Whitesboro, Texas. According to the label, it contains all the protein (14.5%), fat (3.5%), calories and fiber (18%) needed daily, and it's fortified with Stride Horse Feed Supplement. I like that the first ingredient is alfalfa meal. It also says horses should not need any additional hay when fed according to directions. This stuff has allowed me to stop buying supplements without guilt.
If all they get is this feed, you're supposed to feed 1.5-2% of the horse's body weight daily, but my horses are turned out 24/7, and have free-choice hay and grazing, so they get less.
What do you feed your horses? What supplements do you give? Are your horses pastured 24/7, or do they have limited, controlled turnout?