The primary biological hurdle in this mating is the difference in chromosome counts: possess 64 chromosomes (32 pairs). Donkeys possess 62 chromosomes (31 pairs). Hybrids ( ) inherit half from each, resulting in 63 chromosomes .
Understanding Equine Hybridization: The Science and History of Horse and Donkey Mating
Breeding a horse to a donkey requires careful management, as the two species display different courtship behaviors and physical communication cues. Courtship Behaviors
Because of genetic imprinting (the way genes are expressed depending on which parent they come from), mules tend to look and act more like donkeys (long ears, braying voice, but a horse's body shape), while hinnies tend to look more like horses (shorter ears, whinny-bray mix, but a donkey's stocky build).
However, traditional "pasture breeding" (turning a Jack out with a herd of mares) still occurs on large ranches.
A hinny is the product of a male horse (called a stallion) and a female donkey (called a jenny or jennet). Hinnies are much less common than mules. This rarity is partly due to domestic logistics, but also due to conception rates; a stallion and a jenny conceive less easily than a jack and a mare. Physically, hinnies tend to look more like donkeys, featuring the refined head and mane structure of a horse but a smaller overall frame inherited from the donkey mother. Mating Behavior and Breeding Challenges