I'm guessing my old guy is around 18-20 yrs young. We bought him a few months ago for my daughter to learn to rope on him. He also runs a nice set of barrels and is a pretty awesome pole horse! Hes super fun and gentle. He came to us kinda weak in the topline and just meh.... I've switched my barn over to purina. He gets roughly 5lbs of purina sr active a day, plus outlast and I'm half way thru a 5lb bucket of this supplement called Tri Amino by ukele, I wanted topline support without a bunch of added fillers and the Tri Amino fits the bill. I'm super happy with how they are looking. He eats unlimited coastal hay in a slow feed net in his stall when hes not turned out on the pasture. I also feed him Bute Less daily and I've got to say hes barely even stiff anymore even when stalled overnight. I never thought an OTC joint supplement would do what it says but I'm pretty impressed by this stuff!

I wanted to add that all 3 of my tractor supply stores carry the Sr. Active, I dont typically buy from them but if I was in a pinch, i could get it there. They are almost $2 higher a bag than my purina store. Our newest TSC also carrys amplify and outlast too. In fact this new store carrys a lot of things I've never seen in a tsc. Including DAC products and also a few Silver Lining Herbs products. 

Completely off topic comment on my part but ohhhhh. He is

Awww thank you! We call him "Chuy" we absolutely adore him! I stumbled on him on Facebook of all places. He was in Missouri, we live in Texas. I watched videos of a little girl roping on him and we hooked up and made the trip! Hubby roped on him first and then we put our daughter on him and he went right into the box and she scored on him, he was 100% perfect. Then she wanted to try to come out of the box on him after a steer. She was so nervous, her hands were shaking lol! He took total care of her he didn't  budge a muscle until she asked him to go and he just loped nice n slow up to the steer. He goes hard or soft as you need. We handed over the cash right after that lol! Hubby still heels on him and he loves it, hes super nice on the heel side. I love his unique markings myself! Hes got what looks like a smeared cross on his neck. Hes just an overall cutie pie! The gentleman we bought him from said he was a bit of a hard keeper and he fed him about 10lbs of grain a day, he was feeding nutrena. Said that was the only feed he had luck with keeping the weight on him. I was prepared to have to pour the grain to him but hes doing really well on the sr active. I think our hay was a lot better too.

First get his teeth done then have your vet check for ulcers!  Nothing will make a horse loose weight faster that a horse ate up with ulcers and ottb are known for it.  Then make sure you are feeding a good quality feed, then add a cup of rice bran oil or corn oil or wheat germ oil to his feed everyday.  That puts on "cool calories"  Make sure you feed plenty of good forage.  Alfalfa and coastal.  

Once you are certain there is nothing going on with teeth, worms, or ulcers...

I have had fantastic luck adding Calf Manna pellets to my hard keepers feed, one is 30 (was always a hard keeper even as a young guy) and the other is 3. They love the taste of it, dont get hot off of it, and it's very economical. Alfalfa pellets, rice bran, beet pulp, and canola oil are also good things to try. They're all different just like we are and what works for one may not work for the other. I typically give it a solid 60 days of trying something and make sure to take before and after pictures to see progress. Good luck! 

I have a 5 yr old that is a hard keeper too and Purina Equine Senior Active solved that problem for me too.

I like adding in more Amplify for a hard keeper. Purina SR has it in it already but for a hard keeper, I like a 1/2 LB AM and PM to put weight on. My mom's big gelding gets 1 LB AM and PM with his scoop and a half of Senior.