The existence of mules must have been beneficial to those who enslaved livestock at that time, and today we will take a look at it together!
Mule is an interspecific hybrid of a horse and a donkey, and the hybrid born of male donkey and mare is a horse mule, referred to as a mule; the hybrid born of a stallion and a female donkey is a donkey mule. Mules and donkey mules are extremely poorly fertile because the chromosomes are not paired and meiosis cannot be performed normally. And the pelvic bone can't open and close, so it is almost impossible to give birth.
So, why are mules loved by everyone and have been trying to cross horses and donkeys?
Mules have strong vitality and disease resistance, longer life than horses and donkeys, so that the service life can be as long as 20 or 30 years, and the service value is high. There is an old rural saying that "uphill mules, Pingchuan horses, downhill donkeys do not have to fight", in the mountains, when you need a donkey, you will basically use mules, it is heavy, fast, and stable uphill.
Horses do run fast, many breeds of horses are very tall, but they will not be used as livestock to pull goods, pulling carts is OK, but the endurance is not as good as mules. Donkeys are small and physically weak. In contrast, mules that combine the advantages of horses and donkeys are still very powerful. Probably before the Ming Dynasty, the number of mules was scarce, and only nobles could raise them! Later, it was gradually used by the people to pull goods and the like.
Maybe it's also because mules don't have to give birth to children to breastfeed, and they can always be enslaved, which is very convenient.