My horses are out on pasture, the only reason I grain a little is to get them to come up to the gate so I can look at them. They have a tendency to get cut up. If I catch them I will give them a little while I am saddling too. If they are getting worked hard they get grained.
The last trainer I worked for never grained the horses in training. They got alfalfa cubes twice a day. Of course they were stalled, but they were worked 5/6 days a week. They all were in excellent condition and beautiful.
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^^This. I never grain my horses unless they are having issues holding weight, but even then, I go for something more like senior feed or alfalfa pellets for the concentrated fat/protein.
I suppose if I was working them hard on a daily basis, I probably would give them a little something to keep them going, but frankly, it would be virtually impossible for a pleasure trail rider to work their horses so hard that they would need something more.
Even my customer horses, who get worked 4-7 days a week (depending on their needs) only get good quality alfalfa hay and free access minerals. They stay fat and slick and happy.
I am a very firm believer that most horses in the world are grossly overfed. Horses being given full or double rations of grains and sweet feeds when they are nothing more than pasture puffs or pleasure trail horses. I honestly believe that's why colic and founder seem to be so darn common.
Truthfully, if they were my horses being moved to this new place, I would just see how they do with what is available there. Most horses do just fine on free access hay and stay at a healthy weight. If your horses don't, then you can worry about whether to grain them or what kind of grain to feed.