Skinny Gelding .. not gaining weight

My husband and I rescued a gelding a few months ago. He's not starved by any means but is still skinny. I would say he's about 100 lbs under weight (ribs visible but not boney). He had a vet exam when we got him and ended up having a cracked molar removed and a float done. He eats much better now and eats every morsel of hay and grain. He gets good quality 1st cutting alfalfa, safechoice grain with oats and corn oil. He's been de-wormed twice. Once with strongid paste and the second time with zimecterin gold. He has no diarrhea, gets plenty of minerals and drinks a normal amount of water. I'm at a loss and am not sure how else to get him back to his stocky weight. All in all he seems happy and healthy except for his weight. His summer coat seems a little dull but not unhealthy. Any suggestions? I was going to try sand clearing him next...

How much feed? What kind of horse? How old? Sometimes they need wormed a few times with the same wormer.

He gets about 3 large flakes morning and night (heavy flakes). It normally takes him about 2-3 hours to finish his hay. He grazes throughout the day too. We started small on grain and have worked up to about 2-3 cups of oats and 2 cups safechoice twice a day. "Blaze" is a 12 year old quarter horse gelding.

That was going to be my suggestion. If he has sand in his hindgut, he won't be absorbing all the nutrients from his food.

Why are you feeding oats with a complete feed? Also you have to weigh the feed, cups mean nothing.

You need to make sure all the worms are gone. Just because you dewormed him twice means nothing. Typically with safechoice you want to feed about 8lbs per day split into small feedings. The label with advise with weight/exercise how much is to be fed.

I can definitely change how I'm feeding around. Should I have a fecal done on him? How do I know all worms are gone.. if he even has any? Should I de-worm again with zimecterin or something else? I will start him on sand clear too.

I don't want to hit him with a ton of de-wormer if he doesn't have worms, do I? Can you over de-worm?

Why wouldn't you feed oats with safechoice? Is it wrong to add extra protien? I don't see how that would hurt.. Please correct me if I'm wrong :)

Oats is just going to be hot energy, there's no need.

Consult a vet about deworming.

If you want extra protein add some alfalfa.

As this is a rescue horse I highly recommend getting a full blood panel done to make sure there are no underlying health issues you can't see.

Thank you :) I already have an appointment for a full blood panel. Hopefully we can figure him out.