It is a bit of a generalisation but it is strongly founded in statistics. The vast majority of heavy over light crosses result in more heavy traits than light ones. This is information I got from one of my state's top sporthorse breeders who ONLY breeds light over heavy after years and years of experience breeding clydesdale sporthorses. She consistently produces incredibly talented showjumpers and eventers and not one horse that comes from her property is any less than great quality. Majority of her horses are exceptional.
I do think that if you're going to cross such totally different types as a draft and a tb, you really need to know what you're doing. That's why I don't cross them myself. Because I don't have 30 years of experience breeding horses and knowing which draft will compliment which lighter horse.
I love drafts, it's nothing against them, they're just not suitable for my discipline, so a horse with too many draft traits, as much as I love them, isn't going to be suitable for my purposes. I want a horse that's as close to the warmblood type as you can get, if I'm looking at a part draft. It doesn't have to have the massive warmblood movement, it just has to have jumping talent out the wazoo and a relatively tractable temperament.
Certainly from the crosses I've seen, the draft stud over TB mare is a far more common cross (and lovely in its own right), but the TB stud over draft mare is a more consistent cross and you're less likely to get the big head, upright shoulder and posty hind of many drafts. The draft horse population in Australia is not as awesome as the rest of the world, but it is improving.
PLUS, if you look at it from a mare safety point of view, the bigger mare is going to be more easily capable of giving birth to her foal than if you put the TB mare in foal to the draft. Less risk of the foal growing too big for its mother to push it out when it's the mare that's the bigger one. Though most foals only grow to the size available to them (as evidenced by an embryo transfer experiment years ago where a purebred shire embryo was put in a miniature mare, and the mare foaled with no issues), some do grow too large for their mothers, and that's when you have real problems. So why not reduce that risk if you can?
Last edited by blue eyed pony; 04-07-2012 at 08:59 AM.