Thoroughbred Jumper needs to put on a few pounds. Suggestions?

My 17h Thoroughbred jumper seems to have lost some weight without me noticing. I did cut back on his grain rations slightly because he is out on pasture 24/7 and we got lots of rain that made the grass really green. I was feeding him some hay at night, but I guess it wasn't enough to help maintain his weight.

Anyway, my plan is to get him back on a consistent schedule eating 20-30lbs of hay per day as well as being on pasture. And I'm going to slowly increase his grain ration back to what it was. But, should I consider a weight gain supplement? Or possibly beet pulp? His previous owner used beet pulp with his regular diet so I'm really considering putting him back on it...

Thanks in advance!

By the way, I know the cause isn't worm-related or ulcers. He's kept on a consistent deworming schedule provided by our vet and he hasn't had a lot of grain concentrate or stress that would cause ulcers.

How about just free choice hay? Works on my hard keeper.

Beet pulp is good, I feed it to my TBs and my senior. You just need to make sure you don't start soaking it more than a few hours before you feed it because it ferments quickly in hot weather.

This is what is starting to pack on the pounds of my 17h TB 4 yrold Hunter ;)

I personally love stabilized rice bran. Some horses cannot be without a good amount of feed even with hay/pasture - my horse is one of them.