Good quality hay is the foundation at about 2.2lbs per 100lbs of body weight. Then anything else all depends on the horse, his health needs, amount and type of work, is he in a stall or large field where he runs, how often you ride... lots of things to consider. A horse nutritionist can help you create a plan designed for your horse's needs
It really depends on the quality of hay, in what work they’re in, how much feed they personally need and the type of feed you feed.
It really depends on the horse like I ride my horse midday so I like to feed once in the morning and once at night but have hay or grass available but in my opinion I would check with a vet to find out the best for my horses