A mule is the result of breeding a horse mare of any breed to an intact male donkey. The resulting mule can be a Quarter Horse mule, a Belgian mule, an Appaloosa mule, a Tennessee Walker mule, a Miniature mule… the list goes on. Whatever breed you particularly like can be used to raise that "type" of mule. Thus, in my way of thinking, mules are non-prejudiced, as they can originate from any horse breed. Likewise, the father of the mule - the donkey jack - can be any size of donkey. The Mammoth donkey, the largest, is in demand for saddle and draft mule production. Standard donkeys, however, and specifically the Large Standard donkey, can also be used in saddle mule production. Likewise, a Miniature donkey can be crossed with a Miniature horse to produce a Miniature mule. So, the resulting offspring can vary from very large draft mules over 17 hands high to the tiniest of mules under 36 inches. You can create the mule you want in one generation.
An interesting occurrence in mule production is the un-predictability of the end product. Sixteen and seventeen hand mules have originated from 14-hand mares and visa versa. Therein lies the genetic gamble that you must be prepared to take when you desire a certain type of mule. Our personal experience has been that there are some mares who, when crossed with the same Jack, have consistently similar offspring, but other mares will throw a surprise every time. I really don't know why this is, but it seems to be more of a phenomenon in mule production than in the horse-breeding world (it helps to be a gambler at heart!).
Mules come in all sizes, colors and shapes. While the donkey has a strong influence on the build of the mule, the most desirable mules have a conformation more closely resembling that of the horse. The exception to this is the inheritance of the donkey's ears - to the confirmed mule lover, the longer the ears the better! Conformation is important, but to us it is secondary to having a good disposition. The bad reputation that still precedes mules in many areas of North American is a carry-over from when horse mares that were not desirable as horse breeding stock were bred to a Jack to produce something of value. The result was often an animal that could work but carried the same undesirable disposition as its mother, and was generally difficult to handle. Good mares were not bred to good Jacks, thus the mules that were raised for a time in the development of the west were often cantankerous and unpredictable.
Thankfully, those days have passed and now it is becoming more predominant to raise mules out of only good, proven mares. The result is mules that excel in beauty and disposition.