Rural Heritage Mule Paddock

Why Not Hinnies?

by Gail Damerow

"Why are mules more common than hinnies?" a listener put me on the spot during a call-in radio interview about draft animals. When you're live on the radio, you have to keep talking. I explained that a mule is the offspring of a mare and a jack. A hinny is the offspring of a jennet and a stallion. At sales and shows, mules and hinnies are grouped together as mules.

By then I had used up enough time not answering the question, and in the process I remembered something someone once told me. So I finished up by speculating that hinnies are less common than mules because they can be less predictable in both conformation and temperament.

I was not happy with that answer, so the subject remained on my mind. Since then I've been collecting reasons why hinnies, and especially draft hinnies, are less common than mules. Not all of the following reasons make any more sense to me than the reason I rattled off over the radio. Decide for yourself:

  • To produce mules, you need only one jack; to produce hinnies, you need a whole herd of jennets. (This doesn't make sense if you believe people who claim that jennets are easier keepers than mares, and jacks are more difficult to manage than stallions.)

  • More mares exist than jennets, and more jacks exist than stallions.

  • Since there are fewer jennets than mares, the gene pool is more limited.

  • Jennets are smaller than mares, and since the foal grows to fit the size of the dam's uterus, hinnies tend to be smaller and lighter than mules.

  • Good mares are cheaper than good Mammoth jennets.

  • Since Mammoth jackstock is classified as endangered, most breeders use the jennets to reproduce their own kind, rather than to produce sterile hybrid mules.

  • Jennets are less fertile than mares, which are not all that fertile to begin with.

  • Heat is more difficult to detect in a jennet than in a mare.

  • A jack responds more readily to a mare in heat than a stallion responds to an estrous jennet.

  • The conception rate is the same whether a mare is bred to a stallion or a jack, but is lower in a jennet bred to a stallion. (At last we're getting into an area where I feel more comfortable, because scientific reasoning prevails. Researchers have found that whenever two species are interbred, fertilization occurs more readily if the dam has more chromosomes than the sire. Horses have 64 chromosomes, donkeys have 62.)

  • The gestation period of a jennet is one month longer than that of a mare. As a result, jennets don't foal every year, as a mare might, but will occasionally skip a year. Breeding mules from mares is therefore more economical than breeding hinnies from jennets.


Gail Damerow is a former editor of Rural Heritage. This article appeared in The Evener 1998 issue.

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15 April 2012 last revision