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Vajíčka slepic a jejich opeření jsou tématem nejen pro chovatele drůbeže, ale také pro přírodovědce nebo zájemce o genetiku a barviva v živočišné říši. V supermarketech obvykle věnujeme rozhodnutí, jaký produkt si koupíme, méně než 90 sekund - a 85 procent spotřebitelů se při nákupu rozhoduje na základě barvy. Barva tedy hraje významnou roli nejen v marketingu nebo u zeleniny, ale má specifický význam také u domácí drůbeže. Přitom právě vajíčka kuřat a jejich barvy byly odjakživa předmětem zvědavosti.
Have you ever wondered why chicken eggs come in a variety of color-- white, cream, brown, blue or green? According to Michigan State University Extension, egg color is determined by the genetics of the hens. The breed of the hen will indicate what color eggs she will produce. For example, Leghorn chickens lay white eggs while Orpington’s lay brown eggs and Ameraucana produce blue eggs. An Olive Egger, a chicken that lays olive green eggs, is the product of a cross between a hen and rooster that are from a brown egg and a blue egg laying breed.
All eggs start out white in color; those that are laid in shades other than white have pigments deposited on them as the eggs travel through the hen’s oviduct. The journey through the chicken’s oviduct takes approximately 26 hours. The shell takes roughly 20 hour to be complete. Ameraucana birds have the pigment oocyanin deposited on the egg as it travels through the oviduct. This pigment permeates the egg shell resulting in the interior and exterior of the egg being the same blue color.
Chickens that lay brown tinted eggs deposit the pigment protoporphyrin on the eggs late in the process of forming the shell. The pigment therefore does not penetrate the interior of the egg, but tints only the surface of the egg, which is why brown eggs are white on the interior. In the case of an Olive Egger, a brown pigment overlays a blue egg shell resulting in a green egg.
A chicken’s genetics determines egg color, according to Extension poultry specialists. For example, Leghorn chickens lay white eggs, while Orpington’s lay brown eggs and Ameraucana lay blue eggs. You’ve got to hear this … a good way to guess what color eggs a chicken will lay is to take a gander at the hen’s ear lobes. “Generally, hens with white earlobes will produce white eggs,” said Gregory Archer, AgriLife Extension specialist in the Department of Poultry Science, Bryan-College Station.
But all eggs start out white because the shells are made from calcium carbonate. Archer said, more often than not, chickens with lighter earlobes also have white feathers and produce white eggs. Those with colored feathers and darker earlobes will likely produce colored eggs. Nature has its own way of coloring eggs, and it doesn’t require boiling water, food coloring or paintbrushes. Different eggshell colors come from pigments deposited onto the shell as the egg forms in the hen’s oviduct.
| Plemeno slepice | Barva vajec | Pigmentace |
|---|---|---|
| Leghorn | Bílá | Bez pigmentu, čistě bílá skořápka |
| Orpington | Hnědá | Protoporfyrin na povrchu skořápky |
| Ameraucana | Modrá | Oocyanin, proniká celou skořápkou |
| Olive Egger | Zelená | Kombinace protoporfyrinu a oocyaninu |
So, in short, different breeds of chicken deposit different pigments on the shell as it forms, changing its exterior - and sometimes its interior - shell color. While genetics primarily determine egg color, other factors can also influence the color and other characteristics of the shell. A hen’s age can also influence the egg color. As they age, hens that lay brown-colored eggs may start to lay larger and lighter-colored eggs.
Easter eggers can be any other breed mixed with either of these two main breeds. A hen only lays one color of egg her whole life. She does not change colors. As it turns out, the speckles on speckled eggs are just extra calcium deposits. One reason for the speckled-egg spectacle is that speckles are formed when the egg-shaping calcification process is disturbed. Another possible reason is a defect in the shell gland. Then again, it could result from excess calcium in the hen’s system.
A further key player in pigmentation is keratin. Keratin is a strong protein - it is what the bird’s claws, leg scales and beak are made from, as well as the feathers. Keratin is actually an opaque protein which reflects light at a particular wavelength. As the light hits the feather, the keratin layer reflects the short wavelengths of light, such as blues, greens and violets. The longer wavelength is absorbed by the darker underlying layer of melanin; melanin is present in the feathers as tiny granules. As a result, the corresponding blues or greens we see, are not the feather colours themselves but, coloured light refraction. In other words, green plumage arises through yellow pigmentation and light refraction.
Converse dull olive- greens will have an element of melanin involved as well. This may sound a rather easy explanation, but in fact the different effects keratin produces, are determined by its structure. For example, where keratin is made-up with pockets of air spaces, the blues and greens are produced by what is termed light ‘scattering’. The tail plumage of a Cream light brown is a good example of this. In the right light, the feathers glisten with a shimmering blue/purple sheen. Of course, a combination of light refraction from the keratin, coupled with pigmentation, can also contribute to the feathers’ colours.
Specific pigmentation can also contribute to the feathers’ strength depending on where the feather is on the body. Dark melanin gives the feathers greater strength and is particularly common in wing feathers. Only reduces their ‘wear-rate’ quite considerably, but also allows them to better cope with the continual rubbing together. Conversely, white feathers are less robust, and therefore have a higher wear rate.
Albinism; Typically, albinism is the total lack of any pigmentation in the feathers, skin and eyes giving the bird a snowy-white appearance. A pure white bird, but without the pink eyes is not a true albino. Generally, in the wild, albino birds would not survive for very long, as they become more conspicuous to predators. In the jungle, a brown bird would be well camouflaged. If that bird was white, it would draw attention to itself. Also, the loss of eye pigmentation makes the eyes much more sensitive to light, and therefore can affect the individuals’ vision.
Leucism; This can often be confused for albinism, as the feathers take on a washed-out appearance, but not quite to the extent of appearing pure white. Also, it may not cover the entire body, and only be evident in patches; such individuals are often referred to as being pied, or piebald. Such birds retain normal eye and leg colouration, and do not develop the pink as seen in true albinos.
Melanism; Classically, an excess of brown or black pigmentation in the feathers results in the bird taking on a more uniform dark colouration. The eyes are their natural colour, though sometimes the beak and legs can also be black. The state of the feathers’ colours can indicate the health of a bird. Vibrant colours, and the bird is showing good health. Whereas feathers that suddenly become dull and listless looking, can often be an indication of a metabolic problem. An example being where white feathers turn yellow. This is usually a sign of liver disease caused through fatty liver syndrome (Hepatic lipidosis). Poor diet, or nutritional changes can also influence changes in feather colouration, as can some viruses.
Shodnout se na tom, co je zelená a co už modrá, je mnohdy nemožné i pro manželské páry, které společně žijí desítky let. Není divu, že řada jazyků tyto barvy ani nerozlišuje. Barvy se vyskytují ve spojitém spektru - červená přechází z oranžové do žluté, zelená do tyrkysové a pak do modré.
Oddanost Johna Travolty scientologii
Lidské jazyky ale s tímto fyzikálním spektrem nakládají velmi odlišnými způsoby: některé mají samostatná slova pro „zelenou“ a „modrou“, jiné ale obě tyto barvy spojují dohromady, do jedné barvy. A některé se dokonce s termíny pro unikátní barvy téměř vůbec neobtěžují. „Otázkou je, proč?“ ptá se evoluční lingvista z Lumière University v Lyonu Dan Dediu, který se svými kolegy našel důkazy pro nečekanou odpověď.
Lidé, kteří jsou více vystaveni slunečnímu světlu, častěji mluví jazyky, které spojují zelenou a modrou barvu dohromady, a to pod pojmem, který lingvisté nazývají „grue“. Lyonský tým se domnívá, že jde o důsledek celoživotního vystavení světlu; hodně slunečního světla způsobuje stav zvaný „brunescence čočky“, a ten ztěžuje rozlišování obou odstínů.
While genetics primarily determine egg color, other factors can also influence the color and other characteristics of the shell. A hen’s age can also influence the egg color. As they age, hens that lay brown-colored eggs may start to lay larger and lighter-colored eggs. Stress factors like disease, heat or overcrowding may also affect the hen and impact the size, shape and quality of the egg.
Diet can strongly affect color of yolk, but it does not affect the color of the shell. For example, if a pasture-raised hen eats plants with yellowish-orange pigmentation, the yolks can take on a more orange color.
To, že vejce nejsou žlutá, má čistě biologický a genetický důvod - příroda nepoužívá žlutý pigment pro barvu skořápky, ale kombinaci bílých, hnědých, zelených a modrých pigmentů podle druhu slepice a chemického složení pigmentů.
Každé vejce začíná bíle, teprve cestou vejcovodem se na skořápku ukládají pigmenty přesně dané genetickou výbavou slepice. Proto slepice nikdy nesnáší žlutá vejce, ale vždy jen odstíny bílé, hnědé, modré či zelené.
Ať už si vyberete jakoukoliv barvu vajec, z hlediska vnitřního složení nejsou podstatné rozdíly. Barva skořápky neovlivňuje chuť či výživovou hodnotu vejce - ta závisí na krmení a celkovém zdraví slepice, nikoli na její genetice nebo barvě vejce.
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