...In my view confirmation of the horse means nothing. A very large full blood clyde could carry such a load and looking at a horse of that stature one would agree. However the horse is designed to go forward. Its body structure has not changed in a million years.
All the breading humans have done have not changed the skeletal structure of the horse and nature did not design it to carry weight on its back but did design it to go forward...
We haven't bred any new bones, but we certainly have bred for a variety of characteristics that can help or hurt. Short backs, thick legs with plenty of bone, good feet, broad loins - from what I've read, those all help.
While Mia remains a short-backed Arabian, she has a mild club foot, long legs and carries her 875-900 (vet estimate) on a 15.3 frame. She tends to look like a big tough girl, but she isn't as big as she looks. Add to it that she is a klutz, and a heavy rider with poor balance could definitely pull her off balance.
Cowboy is maybe 650, but he is 650 lbs of tank. Great feet. Legs as thick as Mia's. I'd guess his loins are as broad as hers, all on a 13 hand frame. Not sure where I copied this from, but I've got it on my computer:
"Conformation analyst Deb Bennett, PhD, of the Equine Studies Institute, notes that the primary requirement of a riding horse is to bear a rider's weight on the freespan of his back without strain, and that certain conformational qualities can make that easier for the animal. In her well-regarded book Principles of Conformation Analysis
, she offers the following wish-list for weight-carrying ability:
- An excellent loin coupling--broad, short, smooth, and strong, yet flexible for coiling. The circumference about the loin and groin should be about the same as the heart-girth;
- A short to medium-length back;
- A neck set high on the shoulder, with a shallow vertebral curve at the base of the neck;
- Moderately high withers, with a peak that lies well behind the horse's elbows;
- A pelvis that constitutes at least 30% of the body length and slopes from 18-22 degrees; and
- A total body weight of less than 1,450 pounds (658 kg)."
This picture of my 3 horses may help visualize how some horses can handle a higher percentage of weight than others:
Not the best I suppose, but compare body size and leg thickness and length between Mia in the front and Cowboy in the back. It seems obvious to me that Mia would have problems at a lower percentage of weight, although her overall size makes it OK for her to carry me. That's just IMHO, and someone good with conformation might be able to show me I'm wrong...