3 y/o colt, no obvious issues (worming, teeth, etc.) has a hard time keeping weight on this time of the year. Free choice hay, high fat grain, etc. I feel like a bad horse mom. My other horse is doing fine, so trying to figure it out. He did the same thing last year, but I did fine ticks on him last year (none this year). Any advice on what to do or what to feed him?

Have you tried alfalfa pellets? That usually helps a lot. I currently feed mt "hard-ish" keeper around 5lbs of pellets a day, split in 2 feedings and soak it. And I also like stabilized rice bran, like the Manna Pro brand. It doesn't take much of that to see results. 

What is he getting fed now? 

Grass/alfalfa hay with purina strategy atm. Its still winter here so literally no pasture to put him on. 

Purina Sr Active and rice bran are what our 2 that are harder to keep weight on get.  They look really good right now.  Beet pulp too so that their supplements stick to something!

I know you said he's young, but my understanding is that all ages can eat the Sr. . . 

The rest of the time he's not a hard keeper...just in Feb and March. Thanks for the advice...usually I can put one on some extra grain and hay and call it good, but not him.

Have you had his teeth checked lately? He's prime age for lots of mouth changes. 

Did he by chance grow during that time he got thin last year? My old colt would do that. He'd get kinda chunky then be ribby when he was going through a growth spurt. He really only ever grew once each spring like that. And Feb/March is prime time for them to grow usually. It may just be his body going through that? I wouldn't change the grain if he's fine the rest of the year. Just add a rice bran or soak some alfalfa I would say, it's easy to remove once he's back to a normal weight. 

See, that's what I'm thinking too...he has grown and is growing (he actually has withers now, yay! LOL). But trying to figure out if there is a hole there somewhere I'm missing. He's turned out, as much hay as he wants, the grain, mineral block...I keep it pretty simple & generally have good results. 

As far as teeth...he has recently lost some of his baby teeth caps...possibly that has given him some issues?

Mine are chasing that spring grass right now and drop a little weight.. the younger horses just look a little skinnier because they are still growing... I up my horses feed a little this time of year, since you already got the teeth part taken care of...

As mentioned above, Teeth, Teeth, Teeth. The three year old year is the worst for a sore mouth. The horse may eat as much, but because their mouth hurts, they only chew the roughage part of the diet enough to swallow. The result is that the roughage is not well digested in the hind gut, and all that nutrition ends up on the ground behind the horse. Be sure to have your parasite control up to date. 

Start with this, and you will likely find that you are pretty well set. Total diet on a three year old does need to be at least 15% protein. If you are not getting there, you are missing proper growth that you can't get back later. Calcium / Phosphorus balance is important at this age also. This does not have to be complicated, in fact, simple makes it easier to control. When in doubt buy better hay rather than a bunch of supplements. 

I've gotten my hay from the same place the last few years and have had good hay from them. I have started him on pelleted alfalfa. We have no green grass yet, it is still winter here (expecting single digit temps over the weekend). Just feel like I need to be doing something. So frustrating. I do have my horses on mineral supplement. I keep it simple so that I don't have a lot to worry about.

We use Rice Bran to help with weight and bulk.

You can keep it simple. Feed soaked beet pulp mixed with hay cube/pellet soaked, add Forco/probiotic, California trace minerals, multi vitamins, with pure vitamin E, flax seed. This will give a healthy gut that utilizes the nutrients available, providing healthy ligaments, hoof, bone,bloom in coat a win win. And fat ....no grain

More 14% grain per day.  I would feed my yearslings 3 gallons per day.