Silkie chickens are widely loved for their gentle nature and adorable looks. Not many people will say that they are almost completely black on the inside by looking at their outsides.
Silkies have black skin, bones, and dark-toned organs, but their blood is red, just like most other animals. Silkies have a genetic mutation causing fibromelanosis, which is the pigmentation of connective tissue cells. Blood is not affected by this mutation and their blood is therefore red.
When reading up about silkies you will come across the reference of the earliest description of the silkie chicken, which was by Marco Polo in 1298 while he was traveling in Asia. He described a chicken that ”has fur like a cat, is black, and lays the best of eggs”.
In mandarin, the name for silkie, Wu Gu Ji, translates directly to ‘dark-boned chicken’. Silkies originated in china but their peculiar appearance had the whole world enchanted within a few decades and early dutch breeders use to advertise them as a cross between a rabbit and a chicken. They were initially brought to the western world as a sideshow exhibit.
Silkie Chickens Have Red Blood Despite Having Black Skin, Bones, and Organs
To explain this, it is important to know what gives blood its red color. Haem, which is the iron-containing, oxygen-carrying molecule red blood cells consists of, is red. It can vary greatly but on average at any given time, 50% of the total constituents of blood are red blood cells. The other constituents of blood namely, white blood cells, platelets, and plasma, all do not contain any type of pigment constituent that will alter the color of blood to have a darker hue.
Why do Silkies have Black Skin and Organs?
The unusual dark appearance of their skin, bones, and organs are due to melanin, a pigment molecule produced by melanocytes. The amount of melanin produced by these pigment-producing cells varies widely and determines the color or tone of the tissue. The more melanin present in the tissue, the darker the hue.
Fibromelanosis is caused by a genetic mutation that causes the melanin pigment to accumulate in the dermis (a layer in the skin) and in connective tissue during embryonal development. Fibromelanosis is a dominant autosomal gene meaning it is carried by the non-sex chromosomes and that only one copy of the gene is needed to express the trait.
The large amount of malanin produced in silkies and other chicken breeds with fibromelanosis then leads to the accumulation of melanin pigment in the connective tissue cells in bones, the dermis of their skin, and among the connective tissue cells of their organs. Their blood is not affected by this trait as blood does not contain trace amounts of melanin under normal circumstances.
The Peculiar Genetics of Silkies: Polydactyly and Fibromelanosis
The Genetic mutation causing fibromelanonsis
Fibromelanosis originally occurred due to a very particular single mutation on one chromosome thousands of years ago. We know this because the mutation that causes this trait is due to a very specific change on a specific area of one of the autosomal chromosomes and is therefore an extremely rare occurrence. This means that a single chicken expressed the mutation thousands of years ago. Because of its peculiar appearance, it was selected for breeding and the first generation of offspring all expressed the mutation as it is a dominant trait. From there on it becomes slightly more complicated but we can assume that humans selected breeding chickens with this trait to eventually create an entire gene pool containing this mutation. (Dharmayanthi et al. (1), Faraco et. al. (3)).
Today there are 4 breeds of chicken that exhibit this mutation namely the Ayem cemani, H’Mong chickens, The Svarthona of Sweden, and, of course, the silkie. It is amazing to think that a single mutation thousands of years ago evolved into the wide array of genetics we see in these four breeds of chicken today.
Of the four breeds of chicken, only silkies are recognized by the American Poultry Association and have their own list of breed standards.
Polydactyly in Silkies
On the note of unique genetic traits carried by silkies, polydactyly is the term for having extra digits above the normal number for a particular species. Chickens, and most other birds, have 4 toes on each foot, but the silkie chicken breed standard has 5 toes. This is also a genetic mutation that has now found a nearly permanent spot in the silkie chicken genetic pool and is listed as a breed standard of the Silkie by the American Poultry Association.
The Medicinal Properties of The Black-Skinned Chicken
In traditional Chinese Medicine, Silkie chickens are used as a key ingredient in a soup together with ginger, goji berries, and dates as a remedy to help increase female fertility and support the development of a fetus in a pregnant woman. It is also used as a recuperation soup for women who recently gave birth. Silkies are known for their exceptional broodiness and excellent mothering abilities, so perhaps the medicinal properties are derived from a silkie’s traits?
Unfortunately, there is no scientific evidence for this but it does not change the fact that silkie meat remains widely used as a remedy in eastern medicine and is sought after as a warming, healing, gourmet food.
In Javanese culture, black blood has healing properties and deceptive sellers will occasionally alter the blood with squid ink or charcoal to offer their customers the magical medicinal black chicken blood at an extravagant price.
How About Roast Silkie for Supper?
Black chicken meat may be slightly odd on the American or western world dining table but in Easter cuisine, it is considered gourmet food. Although I can’t speak from experience, the black-skinned chicken meat is said to have a unique richness in flavor. Others say that it is rather tough with a gamey taste as silkies are slow-maturing, lean birds compared to broiler chicken breeds that are slaughtered at a young age.
See below the stark contrast of regular chicken and a silkie chicken. Guests will probably not be impressed with my gourmet cooking if I serve a midnight black chicken roast and I am not sure I would take the chance to taste if the opportunity arises but one thing I am pretty sure of is: it will probably just taste like chicken!
References
- Dharmayanthi, A., Terai, Y., Sulandari, S., Zein, M., Akiyama, T. and Satta, Y., 2017. The origin and evolution of fibromelanosis in domesticated chickens: Genomic comparison of Indonesian Cemani and Chinese Silkie breeds. PLOS ONE, 12(4), p.e0173147. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0173147#sec013
- Dorshorst, B., Okimoto, R. and Ashwell, C., 2010. Genomic Regions Associated with Dermal Hyperpigmentation, Polydactyly and Other Morphological Traits in the Silkie Chicken. Journal of Heredity, 101(3), pp.339-350. https://academic.oup.com/jhered/article/101/3/339/839162?login=true
- Faraco, C.D., Vaz, S.A., Pástor, M.V.D. and Erickson, C.A. (2001), Hyperpigmentation in the Silkie fowl correlates with abnormal migration of fate-restricted melanoblasts and loss of environmental barrier molecules. Dev. Dyn., 220: 212-225. https://doi.org/10.1002/1097-0177(20010301)220:3<212::AID-DVDY1105>3.0.CO;2-9
