Mules are sterile hybrids that result from the crossbreeding of a male donkey (called a burro) and a female horse. This combination is done to produce an animal that inherits specific traits from both species, such as the hardiness and patience of the donkey, combined with the strength and endurance of the horse. However, due to their hybrid nature, the vast majority of mules are sterile, meaning they cannot reproduce.
Are mules sterile?
The sterility of mules is due to a chromosomal compatibility problem. Here are some details:
1. Number of chromosomes:
- Horses have 64 chromosomes.
- Donkeys have 62 chromosomes.
- Mules, as hybrids, end up with an odd number of chromosomes, namely 63 chromosomes.
This odd number of chromosomes makes it difficult to produce viable sex cells (eggs or sperm), because meiosis (the process of cell division for reproduction) cannot take place normally. This leads to sterility.
2. Difference between mules and hinnies:
- Mules are the result of crossing a male donkey (burro) and a mare.
- Hinnies, on the other hand, are the offspring of a stallion (male horse) and a she-ass (female donkey). They are also sterile for similar reasons.
The sexuality of mules
Although mules are sterile, they are not asexual. Mules and mules can have normal sexual behaviors like horses or donkeys, and they go through the same stages of sexual maturity. It is not uncommon to see these animals mate with each other or with horses of the opposite sex. However, given their sterility, these behaviors do not lead to reproduction.
The mule has heat cycles like mares, which go more or less unnoticed, on the other hand the mule retains a passionate libido and often without regard for his companions ... It is strongly recommended to castrate them because they have a dominant and violent character, especially with other animals. The earlier they are castrated, the faster they forget this mode of operation
Rare cases of fertility
There are extremely rare cases of female mules (but not males) that have been able to reproduce. In exceptional situations, a few female mules have given birth to a foal. However, these cases are very rare and represent an anomaly rather than a biological norm. The rate varies from one author to another...from one mule per century to 0.005%
According to a study by Meyer (2009). the mule would have spermatozoa in the semen, but of irregular shape and immobile. On 20 mules, the histological examination of the testes showed few spermatogonia and spermatocytes.
In conclusion
- Mules are almost always sterile because of their chromosomal composition.
- They can have normal sexual behaviors, but this does not lead to reproduction.
- In very rare cases, a female mule can conceive, but this remains a biological exception.
The surrogate mother mule
Embryo transfer in mules, although rare, is theoretically possible. This technique, commonly used in horses, involves implanting an embryo from a mare into the uterus of a surrogate mother. Although mules are sterile and cannot produce viable eggs, their reproductive tracts are functioning and can, in theory, support a pregnancy. Mules, combining the qualities of horses and donkeys, could be considered as carriers for valuable horse or donkey embryos. However, this method, complex and expensive, remains little practiced despite positive results in some experimental cases.
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