How would you design a "riding" dog breed?
In my setting halflings are about the size of small human children, and are far too small to ride a horse, so I had the fun idea of them riding large dogs called "saddlehounds" about the size of great danes or saint bernards instead. How would they be built for speed, sort of like a greyhound, yet sturdy enough to be able to support the weight of a small rider?
So, one important reason horses are such good riding animals is because their back stays relatively flat while they're running, even at a full gallop. dogs' backs tend to bend a lot more, especially in breeds that are built for speed.
I found and traced some old photo series of a horse and dog running to show the difference. my references came from a photographer named Eadweard Muybridge, who did a lot of photo series of animals in motion back before video cameras were a thing.
(image description: sketches showing the body forms of a horse and dog running. Each animal is shown with just four sketches, each one in a different running stage. the horse's back remains mostly parallel to the ground in every sketch, but the dog's back curves upwards every time the back legs come forward. end description)
because dogs' backs curve that way when they run, a riding dog will need a different body shape to flatten that out. speed is not the goal here, rideability is.
the simplest solution, I think, is to copy the body shape of a small equine, like a pony breed, and then just give it dog features. dog bellies are a little narrower than horse bellies, because herbivores just have bigger guts, so you can thin it down a little to help it look like a cohesive dog, but the pony body will at least have the right build to keep that flat back while running. and also be sturdy enough to carry people and their belongings.
(image description: sketch of a burly looking dog with a curled tail and floppy ears. its back is flat and sturdy like a pony's. end description)
you can of course adjust the dog features to your liking. I used a shetland pony for the body reference, but any pony will work for this. I specify pony more than miniature horse because ponies just look more sturdy and I think that lends itself well to the idea of a riding dog.
