I have been riding my 14.3hhpaint horse, Five, for seven years now and we’ve gotten pretty solid at training level and have been very comfortable with 3’3-3’6 courses. Five is a super athletic horse, but he’s already 14 years old and has some conformational issues like being two inches downhill, a clubbed right hoof, a considerably shorter right leg, and get sore pretty easily (he is maintained on previcox and will try adequan, too, along with multiple supplements). I was really hoping to start schooling 3’9 and prelim cross country this year so we could maybe start competing at the end of next year. I’ve been told by many people that he’s 100% prelim competent and Lainey Ashker even said he could easily do a cci* (but she didn’t see our dressage)! I guess, what I want to know is how are you supposed to be able to judge at what point you’re asking too much of a horse? Where is their limit? I don’t want to push him so hard that he starts dropping rails and refusing because he just can’t do it, so how am I supposed to judge where his maximum level of competency is without hurting him in the process? I do have a somewhat intuitive feel of when he’s comfortable (he feels best at 3’3-3’6, but rushes fences below 3’, but we haven’t yet schooled over 3’6), but how can I know for sure?
Do you work with a regular trainer that can help you out? They should be able to let you know whether your horse is at the top of his threshold or not. If you are unsure or not educated enough to determine this I would try and get on a regular program with a knowledgeable coach who can help you decide whether you are capable of upgrade.
I would say that now is the time to look for a youngster so you have one to train while you are enjoying the older one competing.
You will know what height your older horse can do as he will stop if not 100% happy at a too high height.
When you decide that he has had enough and is ready to step down or retire, your younger one hopefully will be ready to take over. JMHO.
If he is being maintained on Previcox…I would not push him to Prelim even if he is capable.
I’ve had many horses capable of Prelim and higher…but not sound enough. My personal view is that given his conformational issues and that you are already needing to maintain him on more than just a preventative…I’d keep him at his current level, work on the dressage…and perhaps look for another prospect.
There isn’t really any way to know for sure until you do it. Do some jumper shows at 3’6. Start to introduce prelim xc questions using show jumps. That way you know before you have an issue at a solid obstacle.
However, in your specific situation, I would be concerned about your horse’s soundness. I would not be comfortable competing at Prelim on a horse that needed Previcox for maintenance.
He’s not 100% comfortable at Training without the previcox, right?
If that’s true, I do not think it is fair to him to continue moving up.
Thanks for all of the imput!! Five is mostly comfortable at Training without previcox as long as I continue to do regular stretches and releases, but he is definitely much looser and moves with more ease with the previcox. Because he’s only getting older, I plan on continuing his maintinence work and strengthening him and maybe school some higher stuff by my trainer’s discretion. If he doesn’t continue showing improvement in the looseness of his movement and mucles/joints or if he gets worse because of his age, I will not compete above Training. If I do, it will be maybe once or twice after getting the okay of my trainer, fellow riders, chiropractor, and vet, and only if he continues to seem happy and healthy. Thanks again for the advice, everyone!
Your horse may certainly be capable of preliminary-- but it sounds like you are doing the right thing.
As for your question-- how to determine if your horse is capable? Go sit on a horse who really IS capable of Preliminary, and beyond. It will feel so easy, so effortless…and perhaps in comparison, you will realize how hard your horse has to work at that level.
Smart eventers eventually learn: Just because you Can, doesn’t mean you Should. Always look out for your horse’s best interest and do what makes him happy and sound. 
The answer to your question is: it depends.
A horse may be capable of doing preliminary with a really good rider who gets him to the perfect spot so he has a chance to jump every question using his maximum scope and ability. But the same horse may stop or crash and burn with an average rider who needs him to get her out of trouble.
If he max’s out on scope and cruising speed with a good rider at prelim, then (IMO) he is not suitable for doing prelim with an ammie. A horse needs to have the scope to do at least one level higher than he is competing at with an ammie.
If your horse can go intermediate with a really proficient rider, then he is suitable for you to take prelim. But just because he CAN do prelim does not mean he is a prelim horse.
