This is in response to HannahH's post in the 'snow white down' thread.
Well thank you ever so much Anonymous! I remember about the xanthophyll from school, but had no idea the corelation with feathers on a bird! How interesting! Thanks for the post and sharing your knowledge, I appreciate it. I look forward to reading more of your posts!
Oh, forgot to mention, does the melanocytes dying have anything to do with Mille Fluer's getting lighter as they get older?
Thank you for your post, HannahH. Xanthophyll and other caroteniods will collect in human skin as well....mothers that feed too many carots to their babies will notice that their babies have an orange color.
The germinative layer of the epidermis is the home of the melanocytes. THese are specialized cells which produce a pigment called melanin. Melanin is responsible for skin color. For humans, everyone has the same number of melanocytes; however, the amount of melanin in the melanocytes varies among individuals. People with dark skin have more melanin;those with lighter skin have less. Persons with freckles have an uneven distribution of melanin in their melanocytes. Production of melanin is a hereditary trait involving a number of genes (deffinition: the units of heredity within a cell). There is also one gene in the human cell that allows melanin to be produced regardless of the amount. Without this gene, humans and animals would be completely devoi of skin color, an albino.
Whoa Josh, your showing your colors now! Yes I remember about the leaves actually being cut from the stem too. So I'm assuming there is no cut and dried (no pun there) reason why Mille Fluers tend to get whiter as they get older.
Melanins are natural pigments and many animals have them. The same melanin pigment that colors (naturally) red human hair has been found in red and buff chickens.
Melanin pigments are produced by cells called melanocytes. The melanocytes that color feathers are located at the places at which the feather actively develops (feather germ). Melanocytes that migrate (via blood pathways) into a developing feather germ function only during the growth of that particular feather. (Actually, migrating 'melanocytes' are often referred to as melanoblasts.) The melanocytes die and become incorporated into the feather structure. New melanocytes are required for the coloration of the next feather that takes the place of the original one, via molt or other feather loss. The process of coloring a feather is the process of the melanocyte transfering melanin to the feather (barbule) cells.
Melanocytes are closely related to nerve cells and is one explanation for the fact that survivors of Marek's Disease, the viral pathogen that attacks nerve cells in poultry, have bleached shanks. There are a number of parallels between melanocytes and nerve cells including biochemical pathways for the synthesis of neuro-active compounds like dopamine and chromophores like pheomelanins.
Between the cell nucleus and the outer membrane of the cell is a liquid called cytoplasm. The cytoplasm is the liquid that everything floats around in. In the cytoplasm are various organelles, like the mitochondria. The actual melanin-pigment granules synthesized within the melanocyte are clumped into organelles called melanosomes or pigment granules. These pigment granules are transferred from the melanocyte to the developing feather structure and are what gives the color to the feather.
The genes that modify plumage color interact with the melanization mechanism sketched above. For example, dominant white seems to cause early melanocyte death and interrupts the synthesis and transfer (to the feather) of pigment granules (melanosomes). White Leghorns, for example, do have normal melanocytes in the feather germ but the melanocytes die before they can transfer more than a few melanosomes (pigment granules) to the feather.
The lavender gene seems to 'dilute black' by interrupting the transfer of the pigment granules (melanosomes) but does not inhibit the synthesis of melanin so the melanocyte 'fills up' with melanosomes without transferring much of them to the feather. Lavender is also associated with other (structural) feather abnormalities.
The primary carotenoid found in poultry products is xanthophyll and is synthesized by plants and not animals. Xanthophyll is the yellow of corn and is responsible for some of the color of autumn leaves as is abundant in grasses and clovers (alfalfa leaf, for example). The xanthophyll you see in yellow-orange leaves in the autumn was always there in the green leaf, but it was masked by the color of the chlorophyll. When the leaf dies and the chlorophyll degrades, the xanthophyll is visible. The xanthophyll that the laying hens get in their diet is expressed in egg yolk and the shanks, skin and fat.
Xanthophyll is fat soluble. Frankly, I am not convinced that white chickens that turn yellow have xanthophyll in their feathers. Feathers are largely protein which is a polymer of amino acids. Age and natural oxidative processes that accompany age tend to have a yellowing effect. Also, sunlight is the single most damaging thing to organic polymers. Natural chicken house vapors, such as ammonia, are reactive with organic compounds as well. Many poultry keepers put chemicals, like chlorine (household bleach) in the water to kill bacteria. The effects on white feather color of ingested chlorine are not known. I am highly suspicious that the mineral content of the water provided to white chickens can influence the color. Metal ions in water, such as iron, calcium, copper, and so on, bind very strongly to proteins. Breeders of white chickens would be well advised to control the iron (and other metals) content of the water they provide. I'll bet my last dollar that white chickens that are fed hard water that is high in iron will grow up to be yellow chickens.
To my knowledge, no one has ever performed a chemical analysis of a 'yellow' feather from a white chicken to compare with an analysis of a 'white' feather from a white chicken to see what the real difference is. It would be interesting and it would put to rest many superstitions.
By HannahH on Monday, November 19, 2001 - 11:05 pm:
By HannahH on Monday, November 19, 2001 - 11:11 pm:
By Anonymous on Tuesday, November 20, 2001 - 12:18 am:
I was interested in the lightening of plumage a couple of years ago. We didnt' do any experiments but we considered some. There are examples of chickens that are highly colored in their youth that become white with age.
Ever decreasing melanocyte production, as the bird ages, could be an explanation of this phenomenon. But, it doesn't have to be that. The melanin synthesis within the melanocytes might become less productive with time. Another scenario is that the production of the melanin might remain relatively constant but the composition of the melanin and the structure of the melanosomes (pigment granules) could change as the bird ages.
There are a number of things that can influence age-related color changes.
Thank you again for your post.
By Josh on Tuesday, November 20, 2001 - 01:58 am:
Each chicken has a genetic code that tells the melanocytes in the skin how much melanin to produce.
The chicken's body needs vitamin D to properly absorb calcium and phosphorous. If the chicken lacks vitamin D its bones become weak and rickets results. Vitamin D is manufactured in the skin when a cholesterol-like compound is exposed to ultra-violet rays.
Also, Anonymous said that "The xanthophyll you see in yellow-orange leaves in the autumn was always there in the green leaf, but it was masked by the color of the chlorophyll. When the leaf dies and the chlorophyll degrades, the xanthophyll is visible."
The major reason why plants lose their leaves in the winter is that the length of days shortens, signaling the plant to ready itself for harsh atmospheric conditions. The leaves fall because they are actually "cut" from the stem by an abscission layer. This special layer of cells forms at the base of the petiole, where it later begins gradually to disintegrate. Either before of after the leaf falls, a protective layer of cork cells forms at the petiole base.
The formation of the abscission layer interferes iwth the conduction of materials into and out of the leaf. THis in turd retards the formation of new chlorophyll, and the old chlorophyll begins to deteriate. The green chlorophyll dissapears and the colors it masked appear.
These colors include xanthophyll (produces yellow colors), carotene (produces yellowish-orange colors), and anthocyanin (produces bright red, purple, and blue colors)
By HannahH on Wednesday, November 21, 2001 - 09:18 pm:
To show you how chicken ignorant I am, I thought Mille Fluer was a specific breed, and I've since found out that the "Mille Fluer" shown in McMurray's catalog is really a booted Belgium D'Uccle. I think. Don't quote me on that.
I now know that many breeds can be 'mille fluer' in color. I think I understand that to be correct, please correct me if I'm wrong. I don't have any of this particular breed, but I am drawn to the feathered feet and shanks of some bantams and standard birds.
Anonymous, thanks for the genetics lesson!! :^}