Spontaneous Sex Reversal In Your Poultry
By Jen Pitino, Idaho
A hen is born with two sex organs. One of these two organs is an ovary that functions somewhat similarly to a female human’s ovary. Normally, this functioning ovary is found on the left side of a hen and grows and develops as the chicken matures. It is this left ovary that produces the necessary estrogen in a hen’s body that regulates the production of ova (though these are called oocytes in chickens) and their release into the oviduct tract. The sex organ found on the right side of a hen is not an ovary at all. Rather it is simply an undefined gonad (yet to be determined as an ovary or testes). Unlike the left-side ovary, the right-side gonad in a hen will typically remain small, dormant and undeveloped throughout the bird’s life.
A spontaneous sex reversal occurs in a hen when her left ovary becomes somehow damaged or fails to produce the necessary levels of estrogen. Usually it is a medical condition such as an ovarian cyst, tumor or adrenal gland disease that causes a hen’s left ovary to stop working. A hen’s left ovary is the primary organ producing estrogen in her body. Without the left ovary properly functioning in a hen, the estrogen levels in her body will drop to critically low levels, while conversely testosterone levels will rise. Without proper estrogen levels, the hen will no longer produce eggs.
More disturbing though, a hen, whose left ovary has failed and consequently has elevated testosterone levels in her body, will actually physically transform to take on male characteristics. Such a testosterone-addled hen will grow a larger comb, longer wattles, male-patterned plumage and spurs. Moreover, this hen will also adopt rooster-like behaviors such as crowing.
You might be thinking to yourself, just because a hen with high testosterone levels grows spurs, long wattles and takes to crowing like a rooster — does not make her, in fact, a rooster. It just makes her a very masculine hen. If that was all that happened in a spontaneous sex reversal of a hen — you would be correct. There is more to it though!
When a hen’s left ovary fails and sufficient testosterone levels are reached in her body, the hen’s dormant right-side gonad becomes activated. When the dormant, right-side gonad is switched on, it develops into a sex organ called an ovotestis, which has both testicular and ovarian aspects. Scientists have found that an ovotestis can produce sperm.
A sexually reversed hen with a “turned-on” ovotestis will actually try to mate with the other hens in the flock. There is conflicting information as to whether a hen that has undergone a spontaneous sex reversal and developed an ovotestis can sire offspring. At least one account of a sex reversed hen fathering chicks exists in online reports.
This unusual spontaneous sex reversal in hens is a somewhat rare phenomenon. British chicken expert Victoria Roberts estimates that this condition occurs in about 1 out of every 100 hens. Chances are your backyard hens will not undergo a spontaneous sex reversal. However, with 1-in-100 odds for a spontaneous sex reversal, it is certainly not an impossibility that a member of your backyard flock could transform herself into a crowing rooster.
Even more bizarre, roosters may also have the ability to undergo spontaneous sex reversals. Chicken expert and author Gail Damerow noted in her book, The Chicken Health Handbook, that in 1474 a rooster named Basel was reported to have been burned at the stake for suddenly laying eggs. In 2010, an Italian couple reported that their rooster, Gianni, unexpectedly began laying and trying to hatch eggs after a fox had raided and killed all of the hens in his flock. Gianni the gender-bending rooster was ultimately donated to the United Nation’s Farm and Agriculture Organization for further study. It is unknown what the medical study upon Gianni the rooster (or is it Gianni the hen?) determined.
Naturally occurring sex reversal in roosters is really quite rare (much more unusual than in hens), so much so that some chicken experts have asserted that it is impossible. Certainly, the information available about spontaneously sex-reversing roosters is limited. The fact that there are multiple reports of it occurring does lend some credence to the claims. Moreover, it is well-established science that sex reversals in roosters can be manufactured. There have been multiple studies demonstrating that male chick embryos treated with a sex steroid regiment can cause those birds to undergo sex reversals. Male chicken embryos administered the female sex hormone estradiol will develop ovotestes. More recently, Australian scientists have successfully manipulated the genes of rooster embryos, causing these birds to develop ovaries.
If sex reversals can be manufactured in a scientific lab with simply the use of hormones, then surely it is possible for those conditions to present in nature and cause the same result. Perhaps Goldblum’s character was right. Life finds a way to fill in and fix the gaps in nature.
Jen Pitino is a writer and owner of Urban Chicken POdcast. Dr. Jacqueline Jacob, a poultry expert (whose Ph. D. is in Poultry Science), discusses this rare condition in episode 018 of the Urban Chicken Podcast. You can find that informative interview with Dr. Jacob at. www.urvanchickenpodcast.com/ucp-episode-018/. Additionally shared at the Urban Chicken Podcast website is a report regarding two different audience members’ hens from separate flocks that ostensibly seem to have sexually reversed into roosters.
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