Crossing Male Donkeys with Female Horses Produces Sterile Mules

Mules have a long history as tough working animals.

Domesticated horses can mate with donkeys, and the breeds that are crossed will determine the size of the offspring.

Donkeys or Asses

Donkeys were domesticated around 5,000 years ago, at about the same time as horses. Their ancestors were the African Wild Ass (Equs africanus), but they are now considered to be a distinct subspecies (Equs africanus asinus) with many different breeds.

Donkeys have been used for heavy work, carrying packs, and for riding, since ancient times – they still are in many of the poorer parts of the world.

In more affluent regions donkeys have tended to become pets, or riding animals for children.

Horses

There are over 250 recognised breeds of horse, and many have been used to produce mules – different local donkey breeds crossed with the local horse.

Mules and Hinnies

If the father was a donkey then the hybrid is a mule, and if the mother was a donkey it is a hinny. Hinnies tend to be smaller than mules (with typically smaller mothers), and the American Donkey and Mule Society believes that "The genetic inheritance of the hinny is exactly the same as the mule". This having been said the hinny's head is rather more horse-like than the mule's.

• Horses have 64 chromosomes, while donkeys only have 62. This means that the animal produced from a 31 chromosome sperm and a 32 chromosome egg (or the other way round) will have 63 chromosomes.

• All hinnies are sterile, and they are usually castrated early on.

• The vast majority of mules also seem to be infertile, although females have occasionally given birth successfully. A mule that proves to be fertile is known as a 'molly'.

Mules are stronger than horses (weight for weight), and they need less food. These two attributes have made them useful working animals in the past.

In addition mules have a thicker skin than horses, and their hooves are harder and more resistant to infection. These factors made them very suitable plow animals in parts of America with heavy, clay, soils. The thick skin made them able to withstand extreme weather, and their feet required less attention.

Large Mules

The relatively small size of most breeds of donkey imposes a limit to the size of the mule.

Breeding large donkeys, such as the Mammoth Poitou Donkey, and mating them with large horses, such as the Mulassiere, allowed one region in France to produce an enormous mule - the 'Poitevin'.

This very large type of mule (they cannot really be called breeds) was an extremely useful working animal, but there are very few left.

Source: John Blatchford. http://suite101.com