Mule is a peculiar existence in the animal kingdom, usually by the cross of two different species, donkey and horse, the offspring of the mare and the male is called the horse mule, and the female donkey and the male horse are called the donkey and mule, the difference between the two is that the characteristics of the horse and the mule are closer to the horse, and the physical characteristics of the donkey and the mule are closer to the donkey. However, in the "Compendium of Materia Medica", there are five kinds of mules, in addition to the above two kinds of mules, there are also donkeys and cattle, cattle and horses hybrid breeds, such as "the peony cattle born from horses, for the horse." Nowadays, it is commonly known as a mule. ”
Mules are not a separate species as they are not fertile. The ancients believed through observation: "There is a clavicle that cannot be opened, so it does not produce milk", that is, the pelvis of the mother mule cannot be opened, and even if she can get pregnant, she will be stillborn. In fact, according to modern research, not only female mules have congenital reproductive defects, but the biggest cause of infertility comes from the lack of sperm motility of male mules. In this regard, nature does not seem to be kind to mules in terms of species selection, so it is almost impossible for a mule to have a foal.
The question of whether mules are fertile has long been controversial. According to modern biological principles, mules are also infertile. Because donkeys and horses belong to different species, they also have different numbers of chromosomes, which causes the mule's *** organ to not develop normally. In layman's terms, the number of chromosomes of a horse and a donkey is 31 and 32 pairs respectively, and when crossed into a mule, it becomes 63, leaving only one that cannot be paired. From this point of view, from the moment the mule is born, it is difficult to escape the doom of cutting off children and grandchildren.
Although mules are infertile, they still play an important role in people's production and life. Because mules have stronger physical strength and endurance than donkeys and horses, they are widely used in farmland farming, cargo transportation, and mountain operations. In addition, due to the relatively small amount of food consumed by mules, they are also considered an economical and practical domestic animal.
However, in ancient Chinese literature, there are not many records of the function of mules, and they even appeared as pets for a time. The most detailed record is none other than Zhao Jianzi during the Warring States Period, who was very fond of the white mule he raised, but in the end, in order to save a sick subordinate, he killed the white mule and used the white mule liver to cure the subordinate's illness. Over time, the transport function of mules was gradually discovered, and during World War I, they even became important strategic materials and were exported in large quantities.
Perhaps also because of the large number of intensive use, some reports of mule calves continue to appear. For example, in 1928 in the journal Journal of Heredity, A. Grossr.Groth) reported that there was a horse named "Alder" at the Texas Agricultural College in the United States. In 1923, the mother mule of "Beck" was mated by a passenger stallion to give birth to a foal (B1), which resembled her father and did not differ in appearance from the horse. Since then, similar news has happened from time to time.
As can be seen from here, it is not impossible for a mule to have a foal. There is a consensus on this phenomenon that the mother mule has eggs for reproduction, and the reason for her infertility is a birth defect in the reproductive structure (pelvis), but if there is the wonderful life of nature, or with artificial help, it can also make a "lucky foal" one in a million.