I’m not worried about his height but I’m curious about some growth progression. In the past two weeks or so he (Arab/Friesian, gelding) has almost completely filled out. Gone is the lanky, gangly creature and now he looks like, well, a horse. No changes to diet. His filling out is muscle and the vet happened to be on property the other day and was dumbfounded by the change but in a good way. The only weird thing is he looks rather…compact. So when they grow at this stage is his spine likely to lengthen any? I’m fine with a shortish back from his Arabian side but he’s just funny looking 
Has anyone else experienced this with their youngins? Or am I seeing his true build? I feel like he shouldn’t be set in stone at 1.5 years but the biggest thing he needs is to lengthen a bit to even out his muscles and I dunno how likely that is? Anyone have any glow ups of their long yearlings to adulthood?
His spine is far from done growing, that won’t totally finish until he’s around 5
There’s nothing about a yearling above the knees and hocks that is done growing longer, excepting the radius and fibula. What’s below the knees/hocks is done growing in length. There are some growth plates within the hock joint that won’t be fully closed until around 5 as well.
Thanks. I guess I’ve always equated their spine growing to height (which makes no sense) but of course spine growth would cause him to lengthen, same as humans I was just really taken aback today because I haven’t seen him in 4-5 days and he looks like a 6 year old riding horse. A frequent lesson mom thought he was a new horse and I was taking him to the arena to ride. Nope. Same yearling they’ve been seeing, just wider lol (still has a hint of ribs visible).
Until they are about 2, they can change shape really quickly. Don’t worry, next week he’ll be back to lanky and gangly LOL Wait until he back lengthens but his neck hasn’t caught up 
In our experience, when such a young horse (or child) suddenly looks filled out, it means they have the groceries in place for a good growth spurt! They grow rapidly, right in front of you!! The kid and horse both grew inches, in a very short time! Shoes on horse went from 00 to 2s, in a couple months. Kid needed new, bigger shoes every three weeks! They both went back to lanky at the end of growth spurts, until the next one.
The larger the horse genetics, the longer it takes them to reach finished size, especially geldings. He probably will stay shorter backed when mature, having Arab heritage. Weibe Dragstra raises Arab-Fresian crosses and sells them. They look very nice in his photos, ridden and driven. He might be a resource for questions if you looked him up.
He has tons more changing/ growing to do!!
My young gelding was never gangly or awkward looking and I was so thankful. He not only grew but stayed " filled out looking" as he did.
He might look a little leaner at times when he had a growth spurt but that was all. He was about your boys age at that time.
