Both Appaloosas and QHs have alot of variety within their breeds. Some Appaloosas have longer, smooth type muscle that is good for endurance, (called slow twitch muscling) but some already have the sprinter/explosive power fast-twitch type muscles like QHs do because they share similar and even the same ancestry--- and some Appaloosa lines were bred for sprinting and fast bursts of speed from the beginning.
There are QHs and Appaloosas which have quite a bit of Thoroughbred blood as well, and (depending on the type of TB) that could lend itself to longer muscling. Also horses bred for Western Pleasure in both breeds will not be as heavily muscled, because they are required to perform smooth, slower gaits rather than execute fast starts, stops, and turns.
So, it really depends on which lines in each breed you are choosing.
Its best to breed "like to like" to get the most predictable results--to select mates that will both be the best choice together for producing the same type of build, movement, talent, etc. in their offspring.
For that reason, most people would not pick a heavily muscled horse and breed it to a longer leaner horse hoping for one or the other, or even hoping for a "happy medium" build-- they would start out with 2 parents that were both built for what they had in mind for the foal.
I don't know if anyone has ever done a study or recorded the results of breeding horses with predominantly slow twitch type muscling to horses with fast twitch muscles to document how each muscle type was passed on-- if one was dominant, if the types tended to blend, etc. It would be interesting to know if there were inheritance patterns.
But you probably won't see too many serious breeders mixing the extremes, because they want to have predictable outcomes in the foals they are producing, so they have the best chance at being good for the specific job or discipline they were bred for.
If I was breeding an Appaloosa to a QH-- well, I wouldn't do that JUST to do it. First I would pick what I was breeding for--- lets say I wanted to produce a cutting horse prospect, and I owned an Appaloosa mare who was a good cutting horse -- I would try to pick the best stallion I could find and afford that would produce a foal from her for that job. I would do some research on how they and their relatives were producing for what I wanted, how the lines crossed, and decide from there. Maybe a QH stallion would be my best choice for this Appaloosa mare. Chances are, if the Appaloosa and the QH were both good at their specific job and were from lines producing more horses that were good at that job, they would have similar body types to one another, even though they were members of different breeds.
Last edited by Eastowest; 04-11-2010 at 11:35 PM.