A hinny is a domestic equine hybrid that is the offspring of a horse stallion (male) and a jenny donkey (female). It is the reciprocal cross to the more common mule, which is the product of a jack donkey and a horse mare.
Hinnies are on average slightly smaller than mules in part because donkeys are generally smaller than horses, and growth potential of equine offspring is influenced by the size of the dam's womb. There is debate over whether this is the only reason for the size variances between the two types of hybrid equines. Some fanciers believe this size difference is only physiological, owing to the smaller size of the donkey dam, as compared to mares, which are generally much larger. Others claim it is a natural consequence of the reciprocal cross. The position of the American Donkey and Mule Society (ADMS) is: "The genetic inheritance of the hinny is exactly the same as the mule."
Like mules, hinnies do come in many sizes. 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 Jacks 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.