I'm sure there will be many varied responses, depending on what has worked best for each of us. I myself do not feed my horse anything special. She gets good quality grass alfalfa hay, mineral salt block, carrots and apples, fresh clean water, once a month for seven days she get's bran mash with pysillium. She is blanketed in the winter, sheeted on cool/warm days, fly sheet in the summer. Shavings to lay on, a three sided shelter and lots of exercise, whether it's me riding her, my trainer or just running around the turn out kicking up her heels.
And everyone that sees her can't believe how shiny, well muscled and healthy she looks. Of course she is not the Quarterhorse ideal for halter, so due to her conformation/being an Appendix and not foundation/halter bred, she usually takes a second or third in halter.
This is us at our local show