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September 09, 2007

My Favorite Mule is a Hinny! - Part 2

By Amy K. McLean, Dr. Mel Yokoyama, and Dr. Sue Hengemuehle
Sowhatchet Mule Farm, Inc.
Madison, GA

Part II. Are hinnys different than mules?


The preliminary report indicated the foal was stressed and the lungs were bright red, there was a possibility the foal had passed away from equine herpes virus infection or septicemia. There was some evidence that the foal was stressed and possibly the jenny had an intrauterine infection. Curly, the jenny was later cultured and was cultured clean (no infection was found). One finding in the preliminary report which was interesting was a tubular structure attached to the broad ligament. This structure created a lot of conversation among many professionals in regards to what it was and was the foal possibly a hermaphrodite. The final necropsy report showed the additional tubular structure to be an enlarged blood vessel that is larger in size when compared to a horse. It’s possible that the larger blood vessel is normal in desert creatures like donkeys, mules, and hinnys. The report indicated that the foal most likely died from lack of nutrition and not due to an abnormal organ. Another very interesting event associated with the foal was the results of the karotyping.


This was a procedure I had not requested because after years of foaling out mares and jennys, I felt my experience was sufficient to identify the foal as being a hinny and never once did I think otherwise. The same was true for Sharon Windsor in both of our minds the foal was not a donkey but a hinny. When the foal was submitted to necropsy blood was taken from the foal to genetically identify the species. For whatever reason the blood was not properly stored in the correct medium to verify its genetic make-up but some how and this is where the necropsy results become some what fuzzy to me, a sample of blood or cells were taken and used to karotype the foal. According to Dr. Agnew, the pathologist in charge, when karotyping animals typically ten blood samples are taken for karotyping and the results are 75% accurate, however, the blood was not preserved properly but somehow the karotyping was still done by an expert in pediatrics genetics.


Only 62 chromosomes were counted from this obscure sample indicating the foal was not a hinny but actually a donkey. I’m still not convinced the foal was a donkey due to its physical appearance and more blood samples from known hinnys, mules, and donkeys are in the process of being taken and submitted for karotyping. Also, when reviewing the photos and slides of the foal I had the chance to look at the ovarian tissue of this animal. There was no follicular activity meaning no follicles were present and follicular growth was occurring to produce eggs (ovums) for reproduction. However, typically sterile animals do not reproduce so is this unusual in a hinny or mule to lack follicles? Again, some mules and hinnys in China and Africa (Morocco, Ethiopia, and Kenya) have reported mules and hinnys that have produced foals but would more mules and hinnys have foals if they were bred? When compared to horse foals (fillies) multiple follicular growth could be identified in the tissue. This leads me to believe the animal along with its phenotypical characteristics was a hinny. A sterile animal such as a hinny or mule can produce ovums and sperm cells but not all of them due to complications with genes pairing with one another. Although, maybe this is typical in a jenny foal to lack follicular growth in her ovarian tissue, or maybe this is typical of mule and hinnys, we don’t know because there were no other samples to compare the tissue to. Also, this brings up the question about how many hinnys have been karotyped to compare to and some of the journal articles I have read and reviewed just suggested that typically a mule or hinny has 63 but who really knows because how many mules and hinnys have been tested? So, you can be the judge look at the photos and make up your own mind. Hinny or donkey foal?

Donkeys have 31 pairs of chromosomes or 62 in total. Typically, mules and hinnys have 63 chromosomes, they inherit 31 chromosomes from the donkey (E. asinus) and 32 from the horse (E. caballus) (Trujillo). After reading several scientific articles I am not 100% convinced that all hybrids contain 63 chromosomes and maybe more research needs to be done. Most of the reports I have read in regards to hinnys and mules are the rare cases where both have produced offspring. Even more interesting one article found that an intact male hinny contained both horse and donkey sperm cells in regards to chromosome counts (i.e. some contained 62 chromosomes and others contained 64 but none contained 63 chromosomes) (Trujillo). The mystery continues!

Posted by Guest Contributor at September 9, 2007 05:36 PM