Calorie dense feed?

My retiree needs a few pounds. He lives out 24/7 with a mini who definitely does not need anything.
Looking for a calorie dense feed for him so the volume is low…. And he eats it all. So mini doesn’t get much!
Bringing them in to feed wouldn’t work for various reasons.
Adding oil is probably not going to work either.
Here in Ocala we have lots of options.
Thanks for any suggestions which one to try!

I had my horse on Omegatin + V/M blend for a while which is very calorie dense, but he stopped eating it after a while even with additional grain or alfalfa pellets mixed in.

Purina Ultium Gastric Care. Its high calorie and very well liked.

My older mare did very well on Nutrena Fuel XF. Low starch high fat and she preferred it to TC Senior.

I have my 35 year old mini on this - he’s gotten skinny but is still trit-trotting around like he is 20. I just want a few pounds on him. I think I see a weight gain but it’s only been 2 weeks… I like the high fat and smaller portions (along with his regular feed, which is their Synergy). He didn’t really like the Unbeetable feeds, but at his age, I am not going to argue!