breeding a draft stud to a pony mare

Question
Would it be safe to breed a hackney Arab cross mare to a perchon stud she is about 14 hh and he is 17.5 they told us they have done it before

Answer
The concern I would have with this cross is that both Hackneys and Arabs are small-framed generally with a light bone structure.  Whereas Percherons are, of course, heavy boned and thick framed.

The mare definitely could have a hard time delivering this foal, due to a small pelvic structure.  The foal will more than likely have a large chest cavity making it very difficult to pass over the pelvic brim during foaling.

Not to mention, if you're considering live cover, you would be expecting a mare that weighs maybe 600-800 lbs. to handle the weight of probably close to 1500 lbs.

I honestly could not see a good reason to attempt this cross.  I would consider it too much of a risk to the mare all the way around.