Hinnies are the reciprocal cross to the more common mule. Comparatively, the average hinny has a smaller stature, shorter ears, stronger legs, and a thicker mane than the average mule. The distinct
phenotypes of the hinny and the mule are partly attributable to genomic imprinting—an element of
epigenetic inheritance.
[1]
Physiological arguments for the differing stature of the hinny and the mule cite the smaller womb of the female donkey (dam) versus the larger womb of the female horse (mare). Growth potential of equine offspring may be influenced by the size of the dam's womb. The
American Donkey and Mule Society (ADMS) appears to interpret these differences as wholly physiological, stating: "The genetic inheritance of the hinny is exactly the same as the mule."
[2] Be that as it may, the
epigenetic inheritance of the hinny is not the same as the mule, as "the differences between the mule and the hinny are now known to be caused by genomic imprinting, whereby the expression of a gene is determined by its origin rather than its DNA sequence".
[1]
Like mules, hinnies express broad variation in stature. This is because donkeys come in many sizes, from miniatures, as small as 24 inches (61 cm; 6
hands) at the
withers, to
American mammoth donkeys that may be over 15
hands (60 inches, 152 cm) at the withers.
Thus, a hinny is restricted to being about the size of the largest breed of donkey. Mules, however, have a female horse as a parent, so they can be as large as the size of the largest breed of horse, such as those
foaled from work horse mares such as the
Belgian.
