I am seeing NO answer about the TB conformations that “kill the jump.”
So I got to thinking.
WB’s have a lot more emphasis on the heighth of action at the trot than TBs, where the low action is greatly preferred. Now the supreme high action horses, the Hackney and the American Saddlebred “use their shoulders” a lot more.
After looking closely at an ASB championship class I noticed that this “using the shoulder” consists of the horse bringing its humerus forward much more than “normal” at the trot (and rack) which apparantly aids the high action. TBs will bring the humerus just as far forward when at the higher speeds of the racing gallop and when reaching over the really high jumps, but the ones who do it over the jumps are elevating the front leg much higher than TBs in a racing gallop. I remember reading around 50 years ago that US show jumpering riders were considering Hackney/TB crosses for show jumping but as far as I know no breeders worked on this cross as a long term breeding program.
If the TB jump killing influence on the WBs comes from the different action of the scapula/humerus joint and if the WB breeders NEED an outcross maybe they could consider crossing with the breeds that have the proper scapula/humerus joints. Off hand I can think of three breeds that have this scapula/humerus action, the Hackney, the American Saddlebred, and the Welsh Pony (I am sure there may be others, tell me about them please.) Hot bloods (TB, Arab, Turkomen especially) do NOT have this particular scapula/humerus action. Some Barb lines might have it but since pure Barb breeding is not popular in Europe/America I am not sure.
The French did some work breeding pure Barbs from their North African colonies during the colonial period and of crossing them to French lines of horses and the other hot blood breeds. Of course in Europe the Iberian breeds have an extremely heavy Barb influence and this influence is from when the Muslims “owned” Iberia and with later Barb imports. In the Americas there are the Paso breeds. the Criollo breeds, and a few American Mustang lines are almost pure Barb.
The problem, of course, is that the pure Barb is not a particularly “beautiful” breed, though they are very “handsome” with that elegant Roman nose, and they do not “fill the eye” of someone looking for a perfectly conformed TB. They also tend to be small horses.
As for crossing with the ASB or Hackney, they come with the scapula/humerus movement and have the heighth, but a breeder would have to look long and hard to find a horse than did not have other conformations that would be harmful to what the WB. ASBs can be very refined, unfortunately the refined ASBs also tend to have insufficient bone, their leg joints tend to be smaller, and often are croup high. The main problem with the Hackney horse is that it is solely a harness horse and has never been selected for riding and galloping; many of them are probably croup high also and they are not particularly refined. The Welsh pony has more riding qualities and some refinement and galloping ability (crosses of Arabian and TB blood) and MUCH better bone, but using a Welsh would probably sacrifice heighth, Welsh ponies are not 16 hands high!
EXCEPT for the heighth, a properly selected Welsh Mountain Pony stallion would probably give the WB breeders a good outcross to vary with the TB/hot blood outcrosses, one that would have a chance of not “killing the jump” while bringing in some refinement. If the worry is not so much refinement then a properly selected Welsh Section D Cob would serve since they are taller than ponies are.
Otherwise, consider that if you desire a pure Hot Blood outcross that Barbs still exist. You would probably loose ground on other conformational attibutes for a generation or three but to me this seems to be the only answer to the refinement/not killing the jump WB problem and the conformational problems would probably be less than with a Hackney or ASB cross.
Another option would be to find a 3-gaited ASB with proper bone and broad joints in the legs who was not too stiff in the back. You’d probably have to sacrifice a “pretty” head though. And yes, there have been a few ASBs that made quite satisfactory jumpers. It is just that an ASB that has any hope of competing successfully in ASB shows is an extremely valuable horse and costs a lot of money, so the ASB breeders have seen no need to cater to any other equestrian market.
Yes, now maybe I “see” the problem of WB breeders. I wish you all luck in finding a satisfactory solution. It won’t be easy. For everything except the scapula/humerus action (and the higher hind end action that tends to go along with it) a properly selected TB is the only outcross you need for what you want as a riding horse. Darn that pesky joint!