I have a gelding who is more racy built and I am looking for ideas on building his top line and adding weight. He carries himself collected, moves well, etc but he doesn't have much "meat" on his back. Besides exercises, what feed/supplement will help with adding weight to his topline. He is on a good grass/alfalfa mix now with no grain as he doesn't get ridden hard. 

Hills, backing, varying transitions, trotting ground poles/cavalettis. Anything you can google for back strengthening exercises work. I've found that adding a stabilized rice bran helps bulk their abck up fairly quickly. I do the Max E Glo at around 1 cup a day is all. Nutrena Boost or Tribute K Finish work as well, I've used them all. The Max E Glo is just available to me locally. The butt tuck/belly lift stretches while you groom are wonderful to do as well. Long and low ridinging, get your horse to drop their nose and stretch out while lifting their back. Thats done a lot for mine just at a walk after having 8 months off from injury. 

The Equine Edge Muscle Mass has done wonders for my 31 year.  Helps keep his weight and builds his top line.

Equine Omega Vit E and Finish First Pellets 

Nutrena topline balance. It's made a huge difference in my horse. I switched over to Nutrena safechoice perform and the topline balance and it's been amazing for him. I've gone thru my share of different feeds and I'm pretty impressed with this stuff. Wasn't ever really expecting to be a nutrena fan but I was unhappy with all the other big names so I decided to give it a shot. Glad I did! 

How old is your gelding, when was the last time you had his teeth floated, getting Dewormed. Adding a good pelleted feed as in a Bluebonnet pelleted such as Equilene Complete or Equilene Pelleted. I got a gelding 6 years ago that his topline was awful was really boney and hes thoroughbred on the bottom, put him on the Equilene Pelleted, get teeth done once a year and good hay and hes a different looking horse. His supplements along with everybody else is Forgo and and Sho-glo supplement 

I have looked, but can't find a list of the ingredients. Do you happen to know them, or where I can find them? I went on Nutrena's site but all I get is the feed analysis. 

I dont have the bag anymore, so I'm of no help there. I do know their safechoice perform has the topline balance included into the feed as well. Nutrena also came out with a product similar to purina outlast on their empower line. I'm patiently waiting for my store to get this in as well.