I struggle with the same issues. I have a moderately easy keeping fjord (he’s an easy keeper by any standard other than the fjord standard ) so he wears a grazing muzzle on pasture, has access to a lower calorie grass hay in the dry lot during the day and gets a ration balancer.
But this does not really meet the demands of our sport (CDE during the winter, dressage and trail riding in the summer) so I supplement his ration balancer with Vit E/Se, Tri-Amino and MSM. I also add Guinness and One AC because fjords run very hot (I joke he can get up to 103 just walking to the grooming area… and I’m only mostly joking). He is not a non-sweater, but I’ve found the Guinness and One AC really make a difference in his temp recovery times. They also have access to a salt block but when he works hard in the summer (or any serious fitness work year 'round), I use Horse Quencher with added electrolytes immediately after a hard work, and he drinks that up and licks the bucket.
And even with all that, I had to provide additional protein in the winter when pasture was for decorative purposes only. I found some mini cubes at TSC, Forage Essentials, I think. Anyway, either T&A or just alfalfa, plus they are completely balanced to be a complete ration, so I added that to the mix. Now that we have good pasture I split a half scoop of cubes (and soak overnight) between him and the retiree, add some oil and electrolytes just to give them the second meal when locked in the dry lot.
Seriously, as a lifetime owner of hard keepers, I never fully appreciated the challenges of keeping an easy keeper in correct weight while also in correct nutritional balance. OK for the retiree it is not a challenge at all, but one in work? Yeesh. I’ve never fed so many supplements, it’s more powder than pellets… That might be 50% of the reason he gets the beer, to soak up all the powder. But, he also gets more beer than pellets LOL