Anyone deal with this in a young horse.  I believe mine was caused by a feed change... too much protein. Vet said to put him back on grass. I noticed his knee seemed a little enlarged about 3 weeks ago... I hope I caught this soon enough and doesn't cause any problems.   Can anyone share your experience if you have had any? 

They can come out of it fine, I'd add some mineral and feed grass hay.  

They almost always come out of it with a feed change. Too many people overdo it when it comes to feeding weanlings and yearlings.  You need a good forage, mineral and to balance the calcium/phosphorus ratio. That’s basically what they need. 

Make sure your calcium phosphorous ratio is correct.  Babies have trouble when it's out of balance. 1.1 to 1.5 calcium to 1 phosphorous is correct ratio. Older horses can do fine on more calcium. You never want the calcium to be less than phosphorous. Even in an older horse, you don't want more phosphorous than calcium. It will rob the calcium from the bones to make up the difference and cause weakened bones. 

Babies and lactating mares need 16% quality protein.  Chances are you aren't over feeding protein unless you're feeding straight high quality alfalfa. 

Over the years I've come to feed the following because it works. Year after year.  No epiphysitis. The only problems I had was when I was feeding too much grain. I learned my lesson.   

1 flake (3-5#) of 12-16% protein alfalfa a day per head. For babies this makes up more of their overall diet than an adult horse on the same diet because they can't eat as much.  Lactating mares get 1 or 2 flakes and sometimes 3 flakes of alfalfa depending on their body score. 

Grass (pasture or hay) free choice

1-2# grain. Real grain. Not by products.

Recommended amount of a quality vitamin mineral. Since we are low in selenium, the supplement I'm feeding which is formulate for my area has organic selenium, probiotics, etc...

He is on good quality 2nd cutting alfafla, no grain, LMF Supper supplement. I bought him the first of Oct and he has grown about 2" since then and has really filled out. Wonder if the feed change could have done it? I do believe they fed him grass... I did grass/alfafla for awhile then over to straight alfafla.  so you think I could do about 5lbs alf and all he can eat grass? 

It would be better if he weren't getting straight alfalfa.  See what most people don't understand is grain is high in phosphorous and alfalfa is high in calcium.  So if you're feeding a lot of alfalfa, you can bring the imbalance closer to balance if you feed grain with the alfalfa. If you aren't doing that and don't want to do it, don't feed so much alfalfa.  I would back off the alfalfa to 3-5#/day and make up the difference in his total intake with quality grass. Grass is the perfect horse feed. But it may not have all the minerals, protein or calories they need to grow.  Continue with the LMF. That's a good feed.  

Add msm to their diet. Had a racehorse breeder give me that advice long time ago - to feed it to all weanlings til they're two or forever if you like but Ive never had a problem and I feed a good amount of alfalfa, enrich, and they're on free choice grass. Just plain generic msm it's cheap and easy. Introduce it gradually and feed per label. 

I have managed a lot of these over the years for customers. Avoiding Hot straight alfalfa at this age is right, though some alfalfa in the diet is OK depending on grass hay quality. All the grass hay he wants. Total feed program still needs to be close to 15% protein, but going lower will be OK for now, as long as excess calcium is taken out of the diet. What most people don’t understand is that you are seeing what you did 30 days ago. Fixing the diet will not show immediate results. In fact, the situation may well get worse over the next few weeks even with an ideal diet adjustment. You just need to hang in there with the proper diet even though it looks like things are getting worse at first.