Corn is high starch, high sugar, think horse candy. It's a treat for a job well done here and nothing more. Mostly it's for my chickens.
A ration balancer with some hay pellets is about as low starch as you can get. The ration balancer is pretty rich but you feed so little that it doesn't matter.
Some of the complete pelleted feeds are very low starch. Blue Seal's Trotter is one. I used it for years and years on my air ferns. My oldest air fern started gaining on even a handful of that (small, 37 year old pony) and I switched to a ration balancer with some very low carb hay stretcher to fill her up.
I've got a walker but she came to me in really rough shape in the beginning of winter. I do suspect she will be an easy keeper too. It's been kind of hard putting weight on her only because I can't separate the pony so I have to stand guard over the richer food for the walker. Even the walker isn't getting a bunch of high test stuff. I didn't want to overload her system. Most of her extra fat is coming from rice bran. Tried a few senior feeds but they seemed to make her hot. Tells me she was getting more sugar from them than she needed.
So I'm back to free choice hay, ration balancer and rice bran for fat and calories. I'm also using a very low starch hay stretcher to fill them up because a 16 hand horse gets all it's nutrition from a cup of feed when using a ration balancer.
It's also subzero this morning. They will be getting a bucket of warm beetpulp.
Beetpulp is great food. It is a major ingredient in most of the senior horse feeds and many of the higher calorie performance feeds. It's nutrional value falls somewhere between grain and hay.
Drawback.... lot a calcium in beetpulp, not much phosphorus.
Careful going too heavy with it in a young horse. Can mess up the bone growth. A few cup fulls to add calories will do no harm. For old horses it's a godsend.
I doubt the trainer is going to add all sorts of this and that and make feeding complicated if this is a multihorse barn. Keep it simple. A pelleted complete feed, some rice brain for fat and calories. Make any changes in feed slowly.
Calories per pound chart Calories per Pound Reference Chart
about ration balancers Ration Balancer Reference Thread