Stumbling in Competition Horse

Question
Hello,
I have a four year old appendix stallion (7/8 TB) which I am competing in lower level dressage (1st level at this time) which has a problem with occasionally stumbling.  He does have issues with interference and my farrier and I have been working to correct the issue (especially noticeable when transitioning from collection to extension in the trot).  His dam had the issue as well though he is not nearly as bad.  He is quite competitive and I bred him with the intent of being an upper level (ie Prix St George) horse - his mother went through the same and his sire is a Grand Prix Level horse.  He is a lovely mover and very willing, and ironically when he stumbles, it is barely noticeable during tests though with riding him every day I am able to tell.  I suspect he is grabbing himself from behind, but he is a difficult horse to ride, so I have been unable to get someone else to ride him for me to evaluate the issue.  I have an appointment set up for my farrier to evaluate him on Wed to see if that is the problem since the "corrective" work we have been doing really doesn't seem to be changing the situation.  He is quite fit, so I know it is not that and he is certainly not bored with the work as he is quite happy.  Currently we are trimming him with a longer toe behind to slow him down and a rolled toe in front to encourage faster breakover with a plain shoe.  If you have any suggestions they would be welcomed.  Thank you in advance.

Answer
HELLO AMANDA...Thanks for your question...

Naturally...this is VERY difficult to answer or have an accurate
evaluation or opinion on, without watching this horse in motion.

Leaving him "long" in the back WILL not help with his interference.
He drives with his hind end and delaying breakover with the hind legs will only (sometimes down the road)cause hock problems.

Rocking the toes in front is excellent for his stumbling...I'd want to know, if you haven't yet, had a veterinarian included to evaluate
his travel ??
I personally would!! His mother also having similar problems leads me to believe that something might be congenital ?
Something to think about. Also...you say he's a lovely mover except when he interferes or stumbles. Could he be sore?? That's where a
vet would be a great help.

Without seeing him move...that's the best I have. Myself or anyone else would only be speculation.

Thanks again for asking...Best to you!!
Joepaul Meyers,C.J.F.