Second to the breeding, in light of the recent posts about Polish and 
Egyptian Arabians I am leery of posting this bu I  have to give you what 
I use and what has not worked for me. I breed old line CMK Arabians, 
primarily Crabbet lines with a lot of the Maynesboro W.R. Brown horses. 
They make fine mule mommas. The few times I have crossed half Polish, or 
Egyptian bred Arabians with donkeys I've had difficult mules. I will 
admit that those mares were not the best temperments though, something 
that I attribute partly to their genetic heritage as well as partly early 
training. Saddle seat style horses, halter champions (in general, I 
recognize there are exceptions <smile> and most show horse types won't 
work. Any mares with muttony withers would also be bad choices, your'e 
fighting donkey withers anyway, no need ot make it worse. <g>
The jack you sleect should be a riding style donkey. We have had good 
success with large standards and mammoths. However, a drafty mammoth will 
make a poor mule sire, his mules will be better suited as pack animals 
rather than riding animals. The jack you select should have good riding 
conformation (be sure you know the differences between asses and horses 
before you judge a donkey though!) and have a reasonable temperment. 
Remeber, jackass means what it does because many of them are that way! ;-)
Regarding mules as endurance animals. In the past most mules were bred 
from the poorer quality mares and had that working against them. Most 
mules do not have the speed to be top ten endurance animals but I think 
that will change as more people look for good mules out of top quality 
mares. We breed all of our mares for both mules and horses. If she's not 
good enough for  breeding to a stallion she isn't good enough to go to 
the jack. You don't get good mules by breeding bad mares! Be prepared for 
a lot of hassle both from donkey owners and from Arabian breeders. The 
donkey folks tend to think "damm Ayrabs" and the Arabian folk are 
horrified at "stooping" to breed to a jack. 
Now for the plug. If you are serious please check out our jack and our 
mares. We are currently taking reservations for 1997 and 1998 mule foals. 
Our jack, DW Desert AssTech, is a spotted (black and white pinto) large 
standard out of mammoth parents. We offer frozen semen to the US and 
Canada. We will breed any mare not already bred for a mule and produce 
our foals to order. We've sold mules to people as far away as West 
Virginia. My home pages also have several articles about mules that you 
might find interesting. There is a longears mail list as well.
Oogie McGuire - oogiem@dsrtweyr.com
Weyr Associates - Multimedia and Web Authoring Services & Consulting
Desert Weyr - CMK Arabian horses & saddle mules for endurance and show
http://www.dsrtweyr.com/oogiem/