I was taught that consistency is most important. So I feed the same thing 365 days per year. However, I NEVER feed a horse that is not cooled down properly, and on very hot Texas days, I feed later in the evening. I feed very little grain and lots and lots of good quality hay.
The reason why I asked was because in the summer I stop giving out grain....most of us do around here....my sister in law is no expert in or around horses and insists on feeding her ponies full feed all the time no matter how hot it is....they also stand in 36 x 36 ft pens 24/7 (to afriad to take them out) if you newbies wonder why I get angry a lot you'll understand now......
Early morning and late in the day just before dark. In the winter, when I run out of round bales, I'll give them each a flake of alfalfa, two if it's very cold.