A mule is produced by crossing a male donkey (called a jack) to a female horse. If a stallion horse is crossed with a female donkey (called a jennet) then a hinny is produced. A horse has 64 chromosomes, a donkey has 62 and the mule has 63. Because the mule has an odd number of chromosomes it cannot reproduce.
Certain breeds of horses were used to produce good riding mules and in some cases the mule was the animal of choice by gentlemen and clergy. The mule has greater endurance and stamina than the horse, can carry more weight for its size than the horse and is less excitable than a horse.
The mules ears are smaller than the donkeys but longer than the horse. Its neck is straight or with a slight arch, has a narrower body and has smaller hoofs than the horse. Its tail is more horselike and its eyes are more donkeylike. A mule can jump higher than a horse and can grow to be taller than either parent. The mule is far more intelligent than the horse and 'having a mind of its own' is often regarded as being stubborn.
In 1785 King Charles III of Spain presented George Washington with a Catelonian jack which he named 'Royal Gift'. This mule was used to breed the first American mules.
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