Getting a horse fit for jumping

I would like to start seriously jumping my horse. He is fab at it and I'd really like to take some lessons and get us into the h/j ring and possibly do some eventing next summer.
The only thing I'm a little iffy on is the conditioning work. He is quite fit doing flat work right now and can do an hour of trot /canter work with short breaks and not even be breathing hard at the end. I'm just worried about how his joints will react to the increased workload (he's 5 coming 6). I might just be overly pro-active but I don't want to screw up his joints.
He gets exercised 5-6 times a week, and turning one of those into a schooling over fences day would probably get him fit enough to handle a jumping lesson 1-2 times a month without damaging his joints, right?
Thanks.

He is at the perfect age to start jump schooling him, I have left my TB boy a bit later to start all this sort of schooling because of joints etc. As long as you keep it at a level that he can maintain and not over facing him I think you will be fine.
I don't think a horse has to be really fit just to jump if you started to consider eventing him yes then you really need to look at his fitness but at this stage his fitness level should be sweet. Good luck and happy jumping

Flatwork should take up 75% of his training.

Take him on trail if that's available, and walk uphill, trot downhill. Make sure the footing is stable, and don't let him rush. The purpose is to strengthen his back muscles and hindquarters so that when he jumps, he is using his "engine" and not his forehand.

Talk to your trainer about a schedule. For my horse, it is a full on jumping school lesson once a week, and he is ridden 3 times in between.
Ripley, another, has flatwork 4 days a week, light jumping each time. I'm talking about less than 3 foot verticals, and 4-5 circuits jumping it once. That said, Ripley is very seasoned and not showing lately, so it is easy and gentle for him. Jumping is just for fun for us (Ripley), while Maverick is in a critical training stage.

Good luck!

It sounds like he will be fine, at the perfect age and everything. Just make sure you don't get in his mouth when jumping, this can discourage him from jumping at all if the action is repeated alot.

There's about 2 feet of snow/ice on the ground right now and it's -30C.
He's also schooling second/third level so he knows how to use his engine.
I don't have a trainer that would be able to answer my questions about jumping stuff, hence why I'm asking on here.
Thanks! I'm going to try getting him working more over fences in January.. I'm thinking that 2-3 80cm fences would be what I'd set up.. He's been "free jumped to 4' with scope for more" according to his breeder so I'm not too worried about over facing him.
Cool. I'm uber excited now!

If he was a couple years younger, I would say he's too young... but at almost six, I think he'll be fine to start jumping. I would definitely suggest getting a jumping coach to work with you. It's very hard to judge correctly from in the saddle and having someone else to work with you is so beneficial. I would start really small and gradually work your way up. If I remember correctly, you do dressage right? This is a great way to start jumping. Dressage teaches a horse so much about movement and correct form. Cavaletti poles are great as starting points. But yeah, definitely have a coach work with you. Good luck and let us know how it goes!!

He definitely sounds fit enough! The onyl things I would work on is lengthening/shortening your strides and really snappy lead changes (flying is better), as you will use both of these numerous times on a course.

Yeah..

My bad, obviously didn't read your post well enough! Also we call dressage level totally different things here, so I really don't know what second/third level entails!

so because I haven't left for my trainers yet (-30C weather and diesel trucks don't mix well) I set up some jumps today and pon was really good!
We warmed up, trotted over a crosspole a few times and practiced getting our leads and not taking off.
Then I put up a trot pole before a little 2' thing and practiced leads and stuff and he was super! His cantering to fences is not awesome so I'm just going to leave a trot in or canter in ground rail out for a bit to let him find his distances.
Then I was putting jumps away and he was standing watching me, I finished and "cantered" up to him and he got so scared and started running away, so then I stopped and he walked right up to me, put his face in my chest and was like "mom I'm scared" hahaha.

ETA second/third is like elementary/medium.