Yes they are solid. I noticed at Virgil's that he had colts in one stall and then another and there didn't seem to be any special place where he wanted colts to be put to tear up the place, so to speak. Turned out to be right. Colts can't tear them up, neither can a big 13,000# adult. I swear that 5 year old walking on his hind feet, with fore hooves on the tail boards, and peeking over the top of the stall wall was quite a sight. He could walk like that the full 12 feet of the stall!
If you're serious about installing them, somebody who knows how to work with wood is probably a good hire. Took my barn builders about 1/2 a day for each stall. I've never regretted it and I've never paid any attention to them, not one repair. These are 16 years old, but the ones I had previously were identical and I had them for 8 years. 24 years total without even a nail needing driven. And occupied for the whole 24 years also. Good luck!