GENETIC ORIGIN
The egg-laying with brown shells (we always use the term extra-red egg in the Marans) is due to the unavoidable presence of hereditary genes that are complex and, to date, undiscovered (we speak of "linkage"). "of this character which is therefore unknown).
In addition, the heredity of the extra-red egg is due to the presence of several genes and not of one, some of which would be dominant while others would be recessive.
Under these conditions, this inheritance is automatically reproduced only if the different genes responsible for the brown shells are united together in the genotype of a subject considered.
We are thus in the presence of a racial characteristic, among others besides, for which the laws of the genetics reserve us still many secrets.
We can also note that the genetic characters causing the eggs "cream-white" (themselves not yet decoded and perhaps just as complex?) Would be rather dominant compared to those causing the "brown eggs".
Moreover, if the assertion sometimes heard of a: greater efficiency of the transmission of the extra-Russian egg by the roosters than by the hens, proved to be a reality in the case of the Marans, then it would be possible to imagine that at least one of the unknown genes causing the extra-red egg would be of the "sex-linked" type, that is, present in the double state in the rooster to be expressed, and in the simple state at the chicken to be so much expressed.
As a result, in the breeding crosses for the extra-russet egg, the rooster would obviously transmit, with unclean hens, its genes to all its offspring while the hen, with an impure rooster, could not do so. visually only to half of his descendants.
This could explain the impression of greater efficiency of the roosters in transmitting the characteristic of the dark egg in the first generation. This is theoretically true only in the first generation.
Beware, this situation is indeed misleading; it only describes a mating of subjects that can be assumed to be unclean, at least in part as to the genes associated with the character "extra-red eggs". Eventually, the recessive genes will reappear.
Like this complexity of genetic factors: "brown eggs", one understands then much better why the possible crossings carried out with races outside the Marans can cause the loss of this character "extra-red eggs" in the offspring, especially in the first generation, then make the transmission long very risky to the point of discouraging the most optimistic breeders. To be more convinced, we can recall here the experiment that was undertaken in the years 1967-68 by disastrous crossings of Russian hens with our Marans, which forced, in the end, to step back in this unfortunate initiative.
It should be noted that currently, some hatcheries or professional farms offer for sale "poultry of Marans" which have nothing to do with our pure race (the Marans ©) since they still disappoint for the production of their eggs to hardly tinted! ... not to mention the other phenotypic characteristics which also have nothing comparable.
We have not finished yet to say and to repeat that any crossing "out of the race" for the Marans is to be prohibited categorically.
ORIGIN OF COLORING
The extra-red color comes from the impregnation of a coloring liquid on the eggshell. This fluid is supplied by the spongy tissue of the oviduct, 10 cm from the end of the oviduct, and deposited just before laying.
As soon as the egg is laid, the layer of colored mucus covering the egg dries quickly and the shell keeps the color.
They are therefore mucous glands that secrete dyestuffs and tint the shell. These substances of albuminous origin are provided by certain cells whose biochemical laws are, to date, not elucidated.
On the egg just laid, and still wet, we can alter all or part of this coloring film.
An unfortunate experiment for a chicken whose egg had been stuck for several days in the oviduct had revealed that the successive layers of pigment had accumulated continuously, forming a film of the order of 1 mm. thick and a purplish color almost black.
Unlike the blue-green egg of the Araucana hen which is tinted in the mass, we notice, when we break an egg of Marans, that the internal color of the shell is perfectly white, offering an unexpected contrast and giving coloring, just before laying, as the value of a final signature proper to the breed.
"An identity card"
The deposit of pigments on the eggs is therefore not always uniformly.
In the manner of an impression, as a child with a wet sponge soaked in color, practices, we observe variations in the distribution of pigments according to layers.
The shell is uniform when the impression perfectly made allowed a homogeneous distribution on the whole of the egg. Just as common is the pigmented egg; then appear thin pointillist networks of a few tenths of a millimeter standing on a lighter background. More exceptionally can appear macules very brown, in slight relief, on a light background or much more sustained.
However, these pigment deposits are subject to variations from one subject to another but also over time. Observations carried out at the nest-trap, over fifteen years of breeding, have shown us, in the best layers of extra-red eggs, that an appearance of the shell established at the beginning of lay continued, with some variations, attributing in somehow an "identity card" for each hen.
The definitive qualities of a layer cannot be judged for these characteristics until after the laying of a few eggs from the first layer. These shades then deteriorate very gradually until the sixth month of laying. The best Marans lay eggs that are better in color with the time and the course of the season, it is advisable to select as much as possible this great quality and to eliminate as much as possible hens that would tend to lose too quickly its ability to darken eggs.
Egg competitions in the summer help to highlight the best performing hens in terms of the color of eggs over time.
Also note that in the series of 3, 4, 5 eggs, laid with a one-day stop according to chickens, the first egg is usually more colorful.
This drop in intensity of color, closed by the fever of incubation, marks, in fact, the natural and necessary rest of the oviduct common to all races.
As soon as the incubation fever is over, and from the very first egg, the good ones begin to lay eggs until they molt with extra-rich eggs.
External influences on the color of the egg:
It is important to point out that poor sanitary conditions can significantly affect the color of the shells.
Before any quantitative decline, a drop in color, an abnormal distribution of pigments, a whitish and rough appearance, are the announcement of diseases or parasites. Excessive fattening, environmental changes, diet, stressors, are also detrimental.
The thickness of the shell:
In general, the strength of the shell is closely related to factors upstream of egg production: genetic origin, layer age, feeding, rearing conditions, condition health. This shell represents about 10% of the weight of the egg. In Marans, when these optimal conditions are met, it is found that the strength of the shell is greater than that of eggs of other breeds.
If the empirical observation is easy (when a Marans egg is broken, it is often with a certain difficulty), no scientific proof had attested it until a group of students (promotion 1995-1997) of the Institute of Sciences and Life of the Earth of Puy en Velay looks at the extra-red egg of the Marans. According to the measurements and the calculations carried out, we were able to highlight that Marans hen eggs had a stronger shell than that of conventional eggs.
These eggs would, therefore, have considerable advantages for their marketing, firstly in terms of potential breakages during transport, and secondly in terms of the shelf life of these eggs which is much higher than that of conventional eggs. The thickness and strength of the eggshell of Marans are now scientifically proven.
It is precisely the thickness of this little porous shell with fine and tight grains which, by reducing the gas exchange, avoids the oxidation of the inner tube: the air penetrates more difficulty in the egg and its conservation s 'finds it prolonged. This lower permeability often results in an over hatching waste of about 5 to 10% compared to most other breeds.
The shape of the egg:
It is a hereditary trait that often correlates with the extra red color of eggs. In the best strains, we often find a globular form for which it is sometimes difficult to distinguish the top of the base, distinction yet necessary to the placement of the egg, pointing downwards, in the bins of forced ventilation incubators.
This character of a form almost more spherical than aids is to be sought because all the ancient writings and testimonies testify this phenomenon. Presumably, the genes responsible for this feature are incomplete dominant characters. The cuticle, the inner and outer shell membranes, constitute protective barriers for the Marans egg against bacteria.
The chemical composition of the egg:
This is an important chapter that opens up since it was affirmed during the last 2 or 3 decades that Marans eggs were richer in protein and cholesterol free.
This propaganda would have had the merit to interest ISVT students in conducting a chemical analysis of these eggs using electrophoresis for qualitative assay and Gornall's method for quantitative assay.
Protein assays:
We have, thanks to electrophoresis of the egg white, identified the three main proteins of this egg white of Marans.On the other hand, no specific protein of Marans hen eggs was revealed, as we had been told in the book "Pell-mell of breeding experiments". But maybe we should have done an analysis more accurate to discover this specific protein. It would, in any case, in a minority proportion because the electrophoresis did not allow to detect it.
Determination of proteins on the white of the egg :
It can be seen from this assay that there is less protein in the white eggs of Marans hens (93.02 g / L) than in those of conventional hens (105.68 g / L). However, statements suggested that there was a double amount of protein.
Assaying proteins on the yolk of the egg :
Apparently, the egg yolk of Marans hen would be slightly richer in protein. However, with larger sampling, we could have appreciated this difference more.
Assays on the lipid phase:
The percentage of the total lipid fraction of Marans hens eggs seems to be slightly higher on average than that of conventional hens, although the differences are reversed for some samples. We can, therefore, think that the observed differences are not necessarily significant.
Cholesterol:
On average, cholesterol levels would be slightly higher for Marans eggs. But the disparity of the results reported to each sample does not lead to an obvious difference. It is, in any case, possible to correct the claims concerning the absence or low cholesterol content of Marans eggs.
0 Comments