By: Elio Corti and Elly Vogelaar

Transcription

1 LEGS Part 1 By: Elio Corti and Elly Vogelaar Legs don t come first when describing a chicken. Still they are important, as they have to support the body. They vary with the looks of the bird: set well apart in broad birds; over long and slender in Modern English Game bantams; typically short in Chabo, or feathered all over in Cochins. Apart from the size, also the colour varies: from pale white to deep black. What do we see when we look at a leg? We see the feathered thigh and the notfeathered shank, covered with scales. However, the true thigh bone is inside the body; the first visible part is not the thigh but the shank (tibia + fibula). Then what we call the shanks or in common: the legs, are in anatomical terms the feet (tarsi). Next comes the toes; on each leg 4 in number, but some breeds have 5 toes. (We will discuss that in: Legs-part 2.) The first toe is the rear toe and pointing backwards. Faults and defects Apart from the wanted characteristic length, thickness and colour, the legs

2 also have to be straight and well formed, with the feet set well apart. Knock-kneed (the hocks carried too closely together or inward) or Bow legged (greater width between legs at hocks than at the thighs or feet) are a fault. Males must have a spur on each leg and females should not have spurs; a sore point, because in some breeds for instance the Belgian bantam breeds - the males often don t have spurs. The Ayam Cemani only starts growing spurs when 3 years old. Reliable breeders assure that also males without spurs are fertile. Same holds for hens with spurs. In Game Fowl hens this is often regarded as a token of vitality. Judges have to observe the standard rules though. Right: Knock-kneed Australorp cockerel Left: Plymouth Rock cockerel with too narrow stance. Right: Knock-kneed should not be confused with close heeled as in English Game. Also with the toes much can be wrong. They should be stout and straight. Sometimes the rear toe is turned forward, which is called duck foot ; a serious fault. A crooked toe is sometimes accidental, but more often (especially in the males) can be regarded as a sign of inherent weakness. Webbed feet are serious defects. Also genetic faults can occur, like polydactyly: having (too) many toes, and brachydactyly: causing a missing nail or missing toe phalange(s) of the outer toe. (This will be discussed in: Legs-part 2) Left: Brahma with deformed and webbed toes. Photo: Piet Stokkermans. Colour of the legs In this article we will discuss the colour of the legs. The skin of the legs - as well as the upper sides of the toes - is covered by scales. The pigmentation of the skin involves both carotenoids and melanins. The most important carotenoid is the xanthophyll, which often shares the same distribution area of melanins, resulting in various phenotypes, among which we can quote yellow, white, green and blue legs. The deposition of both pigments is influenced by specific genes which often join - not yet identified - modifier genes.

3 The presence or the absence, of one or of other, or of both pigments, is able to produce an amazing variety of legs colouration, due to the fact that two different sectors exist in which the pigments can settle: the epidermis, more external, and the derma, on which the epidermis leans. The following table synthesizes the 9 possibilities. The absence of pigment is pointed out with the sign -. Leg Colour depending on epidermic and dermic pigment the mark - points out the lack of pigment epidermic dermic Leg colour - - white - black slate blue - yellow straw black - dirty white black black black black yellow dirty yellow yellow - straw yellow black green yellow yellow yellow The colouration of the legs doesn't depend only on genetic factors. We have to consider the fact that also the age of the chicken is responsible of the colouring. In fact, at hatching, the colour of the legs is an unreliable moment to foresee the adult colouration. As an example, yellow legs at birth can turn white or green in mature age. Chicks 4 weeks old with green legs, when adult can show slate blue legs. With years' elapsing, the intensity of the colouration grows weak, so that this will possibly result in straw coloured or faint grey legs. Therefore we have to watch out for not pretending, as the standard expects, a colouration of the legs of identical degree in subjects of different age: they cannot compete because of pure physiological reasons. The diet often has a non indifferent weight, since with the input of carotenoids, contained in grass and maize, an intensification of the yellow is often gotten. A bad state of health, as well as specific illnesses as coccidiosis, have the tendency to make the yellow legs to turn pale. At the cost to be pedantic, the judges have to remember to ask if a female, with eyes and legs poor in carotenoids, is either ill or a very good layer. Left: A black Wyandotte with yellow legs. 1. PIGMENTATION BY CAROTENOIDS The carotenoids are responsible of the yellow colour of skin, legs, beak, fat, yolk and sometimes of the eye. They are pigments of vegetable origin. We should remember that - otherwise from what happens in Canaries, Parakeets and Flamingos - the carotenoids don't have any practical importance in the pigmentation of chicken's plumage. The xanthophyll is also present in the chromatophores of the iris, where, combining with the red colour of the capillary bed, produces the colouration called bay eye.

4 The yellow colour of the skin is a characteristic trait in e.g. Leghorn, Plymouth Rock, Cornish, Rhode Island, Brahma and Cochin. On the contrary, Orpington, Dorking, Sussex, Langshan and Minorca don't have skin carotenoids, neither in the legs AUTOSOMAL WHITE SKIN W+ - white skin Autosomal dominant III group of association - chromosome 1 W stands for white. This gene is attributed to the Red Jungle Fowl, in which it inhibits the laying of xanthophyll in skin, legs and beak, while iris, yolk and blood contain a normal amount of carotenoids. In the breeds in which the gene dermic melanin id + is present, the legs are slate blue. Left: Orpington cockerel with white (pinkish) legs. Photo: Archives AE YELLOW SKIN w - yellow skin Autosomal recessive III group of association - chromosome 1 Allele of the previous one. The yellow or white skin can be surely identified only at the age of weeks and the diagnosis is complicated by the diet that, if poor in carotenoids, can cause a pale straw-yellow skin even if the subject is genetically w/w. The w/w homozygous subjects show comb, wattles and earlobes that, when red, have a very high orange tonality, being that the xanthophyll overlaps the red. In the same circumstances the earlobes, if genetically white, take a saffron dusting. If the dermal melanin id + gene is present, the legs are olive green. The yellow's variations of intensity in legs is also influenced by genetic factors and by the sex of the bird. Chickens of the same breed, receiving the same food ration can differ in a marked way and usually the males have more intensive yellow legs in comparison to females. Among the causes of genetic kind are included - besides unknown modifier genes - also sex-linked concomitant causes, among which could be counted the B gene (sex-linked barring), able to brighten the yellow legs. This observation, due to Jaap, is based on a white Columbia chicken and later this researcher has been able to establish that the effect is dose dependent. Right: Judge Margriet Maas, holding one of her black Leghorns. Note the yellow legs and the saffron ear lobes. Photo: Archives AE.

5 1.3. SEX LINKED WHITE SKIN y - sex linked white skin Sex linked, recessive V group of association - chromosome Z Its action consists in eliminating the xanthophyll from legs and skin, while the abdominal fat and the yolk are yellow. Nevertheless we have to underline that the yolk of y_w + females is paler in comparison to the genotype Y + _W + or W + /W +. In the same manner in the subjects homozygous_hemizygous for y we find a reduction of the plasmatic level of xanthophyll. The white skin phenotype due to the sex-linked y gene can be carefully determined in new born chicks, while this doesn't happen in the autosomal genotype W + /W +. Right: At hatching, the colour of the legs of this Gournay bantam chick was yellow, but in mature age they turned whitish with black spots. Left: Gournay bantam cockerels with the correct leg colour. Photos: Archives AE. 2. PIGMENTATION BY EUMELANIN prototype is represented by Silky. The melanin of all the districts different from plumage is only eumelanin, being that the pheomelanin is present only in feathers. The eumelanin is present in the following anatomical structures: epidermis, derma, eye, mesentery, peritoneum, testicle, adventitia of blood vessels, connective of the band tightly clinging to the external surface of the superficial abdominal muscles. Its presence or its absence depends on the genotype, with total absence in the recessive or autosomal albinism, c a, tyrosinase negative, and in extreme quantity in the fibromelanotic genotype whose 2.1. EPIDERMAL MELANIN The epidermis of the chicken generally contains very scarce eumelanocytes, with the exception of the eyelids of normal subject and the areas of the head in the phenotype gypsy face or blackberry face. The genes more responsible of epidermal eumelanisation are two: E of the extension of black, and that of golden brown E R which is less effective. The effects of E are more evident in the legs and, if certain eumelanin's inhibiting genes are missing, often the legs are black. The black legs due to the genotype E/E succeed in also preserving some pigment in the derma in presence of dermic melanin inhibiting gene Id. The effects of E R are inhibited with more facility. Right: Australorp cock with black legs. Photo: Archives AE.

6 The most powerful inhibitor of the epidermal melanin in the legs is the dominant white I, which, as we know, is able to prevent its deposition also in feathers. Also the genes of the autosomal barred B and of the speckled mo are able to inhibit the deposition of melanin in the epidermis of the legs. If they are eumelanotic speckled, the legs are rosy white or yellow depending from the genotype related to the deposition of carotenoids, with small black or grey residual epidermal scales. The effect of B is dose dependent, then, if the desire to get males with female barring is imperative, you have to pay the penalty for darker legs and dark beak too, while this would not happen for an homozygous male. Above: Black Polish have slate blue legs, but cuckoo (barred) Polish have whitish legs. Photos: AE. Usually the Ml gene of melanism is regarded as endowed with exclusive action on plumage. After observations of Ab-Der-Halden this gene is also responsible of the presence of epidermal melanin and this allows to explain the different tonalities of grey in legs. If the gene of melanism is in the patrimony of a sex-linked barred, the legs will have the tendency to not have epidermal melanin, since in this area the gene B inhibits Ml. The epidermal melanisation of face, comb and wattles is characteristic of the phenotype gypsy face or blackberry face, showed by Sumatra, Modern English Game with genotype E R with or without silver addition; the same phenotype, even though in smaller degree, also by the Sebright is possessed. Right: Gypsy face blue birchen Ardenner bantam. Photo: Ruben Boonen. The confirmation that in this phenotype the epidermal melanin is involved, comes from the observations of the breeders, who observed that the face further tans with the exposure to the sun. In 1987 Auclair didn't succeed in intensifying the pigmentation of this district resorting only to ultraviolet rays in subjects with dermal eumelanin, that is those endowed with the gene id +, and he didn't even succeed in his intent in fibromelanotic subjects.

7 Being that these phenotypes with dark face are often endowed with the gene E or the gene E R, could give that the cause resides in such alleles or in some similar allele. Nevertheless, quite a lot of phenotypes tied to E, as well as to E R, have a beautiful bright red face devoid of epidermal melanin, and the same also happens in those having the dermal melanin due to id +. At present knowledge cannot be affirmed either the phenotype gypsy face is due to an allele of the locus E or to a modifier gene endowed with dominance towards the genes E and E R DERMAL MELANIN Although dermal melanocytes are scarce in the skin districts, their presence in the derma of the legs is a characteristic possessed by a lot of breeds. The eumelanisation of the derma is under the control of genes brought by the chromosome Z. The slate blue or slate grey legs, as we want to call them, are due to dermal melanin, not accompanied by epidermal melanin. In slate legs the epidermal horny layer, which is clear, alters the tonality of the underlying black pigment. Among the breeds with slate blue legs, skipping the Red Jungle Fowl, we can list: Hamburg, Polish, Campine, Fayoumi, Dwarf of Java, Buff Catalan, Sultan. Left: Lakenfelder cockerel with slate blue legs. Photo: AE. Left: Pencilled Hamburger pullet with slate blue legs. Photo: Klaas v.d. Hoek. The standards are essential, they represents a guarantee for the maintenance of the purity, they are a rampart against the today's relativism, they infuse surety and hope. Nevertheless, the Judges have to be relativist, also conciliatory if necessary and above all they have to be naturalists. Even if they didn't have the fortune of travelling in far-away lands, they must possess a culture going beyond the canons imposed by people barricaded behind the standard, in a breathless search of protection against personal insecurities that don't have any bond with the aviculture. Someone will say: here is Corti, the newly pain in the ass with his Pindaric flights soaked with defeatist philosophy. It is not defeatism. If somebody would like to accuse me of defeatism against poultry judges and also against their intransigent statements, I have the support of Mr Blyth quoted by Lewis Wright, who reports as Mr Edward Blyth had noticed that the majority of Red Jungle Fowls of Indian subspecies had leaden blue legs, while the subspecies of Java and Malaysia, respectively javanicus and spadiceus, were showing a clean yellowish colour, a distinct yellowish tinge. The affirmations of Blyth must lead us to be not absolutist at all in our affirmations, as often contained in poultry standards. This means that we can discuss until nausea about the correct leg colour in Gallus gallus. But since all mentioned wild species are known today as being ancestors of our domesticated chickens, we do have to accept the variability in leg colour.

8 The same discourse on the variability of the colour of legs can be applied in the Phoenix. I remember that at the beginnings of my breeder career there didn't exist the same opinion about the colouration of the legs of this breed, since some accepted them yellow, while on the contrary others wanted them slate. The genetics is history, then the reason of this wavering is explained in Le razze della gallina domestica (1905) by Teodoro Pascal: The types imported in past times from Japan didn't have fixed characters, so we had individuals with a curly comb, others with a single comb, at the same time some had yellow legs and beak, others had them greenish or grey, and the same holds for the shapes and the mantle. Glancing both the American Standard of Perfection and the standard of American Bantam Association, doubts don't exist: the legs in the Phoenix must be a leaden colour. The Dutch standard is not only more flexible, but it hangs in the opposite side, since legs and toes can be slate blue, or better, dark olive green; a genetic precondition of the yellow legs - leiblauw of liever donker olijfgroen. Relativism? Flexibility? Genetics? Naturalistic culture? Perhaps all together. The Dutch people stand out for being in the forefront about the colourations, opposed by certain conservative German ringleaders. Conservatives of what? A diatribe of this type would occupy the sessions of the Entente Européenne for lustres, with the victory of the more neurotic persons. The green legs are a characteristic of Sicilian Buttercup, in which the colour takes origin from the contemporary presence of carotenoids, absent in the slate legs DERMAL MELANIN id+ - dermal melanin Sex linked, recessive V group of association - chromosome Z The gene responsible of the dermal melanin, taken for granted in the Red Jungle Fowl, is recessive in comparison to its mutant allele, able on the contrary of inhibiting the eumelanogenesis in this district. Then the abbreviation of this gene begins with the lower case letter i. Its action becomes evident at about three months of age and is independent from the genes controlling the pigmentation of epidermis and plumage. In fact the dermal eumelanin is not eliminated neither by I nor by c genes, even if both these genes are able to dilute it. They are known other inhibitors of id + : barred, speckled, dominant and recessive wheaten, as well as Di. The contemporary presence of the genes id + and Ml gives a deposit of dermal and epidermal melanin, with black legs; if the gene Bl is present the legs are bluish. Above: Bresse cockerel with slate bleu legs. Photo AE. Right: Combattant du Nord cock with olive green legs. Photo: Dirk de Jong. In the French region of Bresse the gene id + seems to be responsible of the naturally bluish abdomens of certain chickens. The inexperienced people consider such colour as a beginning of putrefaction. The Combattant du Nord (Fighters of the North, French Game Fowl) used in the gallodromes, according to the standard, very often have olive green legs due to the union of id + /id + with w/w, and the same colour is found in strains of Fighters of the North crossed with Belgian Fighters. While in France chickens with yellow skin were for a long time

9 synonymous with meat of bad quality, in England the black legs are discredited. Under the French influence the English people have modified their preferences INHIBITOR OF DERMAL MELANIN Id - dermal melanin inhibitor Sex linked, incompletely dominant V group of association - chromosome Z The incomplete dominance is demonstrable from the fact that the heterozygous males show a melanic pigmentation of legs which is present, but weak. Id, being sex-linked, cannot be transmitted from mother to daughters, then this fact could be exploited for sexing hybrids whose mother is hemizygous for Id and the father is homozigous for id +. The male descendants will show white or yellow legs, while the female descent will be endowed with slate blue or green legs. The most recent studies have shown that the locus Id possesses many alleles. The overwritten letters point out the breed or the strain from which the presence of the single alleles has been deduced DERMAL MELANIN CORNELL idc - Cornell random bred White Leghorn This mutation differs from the wild id + because, nevertheless being a Leghorn with genotype I/I, the pigment is present both in plumage and beak. In this same strain it has been possible to observe that the females hemizygous for id c and with green legs are meaningfully more susceptible to the haemangiomas (overgrowth of blood vessels in the skin) in comparison with their sisters with yellow legs, and therefore hemizygous for Id. Left: Hybrid pullet with green legs. Photo: Elio Corti. Right: Ancona pullet with spotted legs. Photo AE DERMAL MELANIN ANCONA ida - Ancona This allele obviously allows the deposition of dermal melanin in the legs and its existence has been deduced in the Ancona because of small green spots. Nevertheless the data are not fully convincing to admit the existence of this new allele, since the phenotype could be explained through an interference by mo, or with the intervention of modifier genes, or more simply with the deposit of xanthophyll at epidermal level in narrow areas without uniform distribution, cause of evident troubles for the breeders of this completely Italian breed.

10 2.7. DERMAL MELANIN MASSACHUSETTS idm - Massachusetts This mutation appeared in a lineage derived from the crossing between black Langshan and a commercial meat lineage with dominant white plumage. It differs from the previous alleles being recognizable only the chicks of a day of life with genotype E, E R, e +, as well as in the chicks with recessive white. The id M allele provokes the blackest legs when its action is combined with the gene E. With a genotype c/c_e/- the colour of the legs is sometimes diluted, but it is still intense slate. It is not expressing in the genotypes dominant white, but the combination I_E gives as result a slate or a pale green colour at the age of weeks GENETIC BASES OF LEG COLOURATION The phenotypic expression in chickens of the colouration of legs and feet depends on the interactive and cumulative effects of some greater genes with not identified genes modifiers able to improve or to reduce the eumelanin. The effects of the genes id + and Id are confined to the derma, while the effect of E takes place above all at epidermal level, but it is also able to add a varying amount of eumelanin to the derma. The gene I is epistatic on the epidermal melanin, but at level of the derma it only succeeds in diluting the pigment, not in eliminating it. Also the recessive white is endowed with a similar action. The genes B and mo are the most greater inhibitors of the epidermal melanin of the legs. Additionally to this, the absence or the presence of the carotenoids (due respectively to W + and w) interacts with the eumelanin of the derma giving slate blue or green legs. Left: Sumatra- black legs with yellow soles. Phto: Wanda Zwart. Right: Black Orpington with black legs and whitish soles. Photo AE. Despite the numerous studies on the genetics of legs colouration, there still exist some variations that have not received an exhaustive explanation. The genetic deductions have some historical stages, consisting firstly in the discovery of the loci E and Id, with the demonstration that the allele of extension of the black E results in legs of a more intense black colour than the genotype E R. Nevertheless this last gene can be present in completely black subjects if joining the necessary intensifier of eumelanin genes as Ml. This explains why subjects exist with completely black plumage with melanin barely present or absent in the legs since they have a genotype E R : if the melanin is present, it is epidermal and it is due to the combined effect of Ml and E R. Other puzzle is the comparison of a thin green colouration extended to the whole leg or only to a part, in apparent absence of the gene id +. Other observation: the gene B eliminates the dermal melanin in the white dominant and white recessive subjects, but it intensifies it in presence of the gene Co. As last, as already said, the gene Co is able to reduce the intensity of the yellow legs.

11 Interactions in which are involved the greater genes of the pigmentation in determining the colouration of the legs carotenoids dermal melanin epidermal melanin genotype phenotype of legs E W + W + IdId EE almost black legs with white soles Id e + W + W + IdId e + e + white legs and foot W + w id + Id id + E W + W + id + id + EE black legs with black soles e + W + W + id + id + e + e + slate legs with white soles E ww IdId EE almost black legs with yellow soles e + ww IdId e + e + yellow legs and foot E ww id + id + EE black legs with yellow soles e + ww id + id + e + e + green legs with yellow soles 2.9. FIBROMELANOSIS Fm - fibromelanosis Autosomal incompletely dominant Group of association unknown Right: The black legs of the Cemani. Photo: Jan Steverink. The characteristic bluish black colour of the skin of the Silky is due to dermal eumelanin and not epidermal, present not only in the immediately underepidermic layer, but also in the deepest derma; the so-called loose connective. The pigment is also well represented in the parietal and visceral peritoneum, in the periosteum and in the perichondrium. Also the blood vessels and the nerves don't escape the hyperpigmentation, which winds these structures, and not even the connective of the entrails is exempt from it. According to the observations of Stolle, in the first eight days of incubation the number of melanocytes present in the connective of a Silky and of a partridge Leghorn is roughly identical; after that in the Silky the amount of melanocytes shows a sudden rise, while in the Leghorn they die and are phagocytized. The numerical increase occurs even if the skin of the Silky is put to live in a different environment, as shown by grafts in embryo. Has been Stolle (1968) to propose the genotype of fibromelanotic subjects, affirming that the phenotype results from the interaction between id + and an intensifier endowed with dominance, to which Hutt had assigned the symbol Fm. According with the data of Stolle, the combination of these genes gives origin to the following degrees of pigmentation of the connective: Combination of genes and intensity of connective pigmentation locus Fm locus Id connective Fm/- id + _- or id + / id + very dark Fm/- Id_- or Id/- few pigment fm + /fm + id + _- or id + / id + without pigment fm + /fm + Id_- or Id/- without pigment

12 Right: Cemani foot soles are also very black. Photo: Jan Steverink. In past times other researchers reported about marked variations about the entity of the fibromelanosis, which suggests the hypothesis that some modifier genes are involved, which are able to change the phenotypic expression. Some of these genes can be in relationship with those responsible of the colouration of the plumage, although the Silky is present in the colourations white, black, blue, pearl grey, buff and wild. Being partial the dominance of Fm, the result of the crossing of Silky with other breeds must be studied point by point. A crossing with a common hen produced a, so to say, melanotic mosaicism: black beak, legs and feet, with remaining white skin. Above and right: This Chabo (Japanese) pullet could be Shinguro variety, with black head, comb, eyes, legs and nails. She is not a pure bred Shinguro though, as her legs are olive green and the foot soles are yellowish. Photos: Greg Davies. An even more extended article on leg colour and skin colour by Elio Corti can be read at in Italian language and also translated in English. Copyright 2009 Aviculture-Europe. All rights reserved by VBC