I am looking for a low calorie feed for my Connemara who becomes overweight very quickly. He competes at top level showing so needs something that promotes top line and muscle development.
Enough Protein and correct work is the best thing for top line and muscle, a lot of my showing friends feed Saracen feeds Equijewel and I think the other one is relieve, when I did showing with my Arabs who are really good doers I just fed grass chaff a good balancer like progressive earth pro balance and micronised linseed, they didn't need high calorie feed or energy feed but looked great on that.
There are loads of protein products out there. I would second using BCAA's, but there's also muscle builder from science supplements, GWF do a high protein top-dress if you want something simple ad ready done, or you can add in things like whey, pea, spirulina or hemp protein.