Translated from the French
by Katherine Anderson

The Marans' eggs

The Marans egg is without any doubt the darkest hen’s egg. This is a characteristic shared with the Spanish breed Penedesenca, but it is accompanied exclusively in the Marans by a spherical form, a size and a brightness above standard.

stippled egg



The laying of brown-shelled eggs in the Marans is due to the inescapable presence of hereditary genes that are very complex and, to date, undiscovered (“the genetic linkage” of this characteristic is therefore unknown).

The complexity of the inheritance of extra-russet-red egg colour would result from the presence of several genes and not of only one, of which some genes would be dominant whereas others would be recessive.

Given these conditions, the heredity of dark brown eggshells is automatically reproduced only if the various genes responsible for the brown shells are joined together in the genotype of the subject considered.

We are thus well in the presence of a breed characteristic for which the laws of its genetics still hold many secrets.

We can note in addition that the genes causing “creamy-white” eggs (these even not decoded to date and perhaps quite as complex?) would be rather dominant compared to those causing “brown eggs.”

Moreover, if the report which is made of a greater effectiveness in the transmission of the genes for dark eggs by cocks more than by hens is proved to be a reality with concrete cases in the Marans, then it would be possible to imagine that at least one of the unknown genes causing extra-russet-red eggs would be “sex-linked”, i.e. present in the double state in the cock.

Consequently, in ameliorative crossings for extra-russet-red eggs, when a purebred cock is mated to a non-purebred hen, the cock would visibly transmit his dark-egg genes to all his descendants, while a purebred hen, if mated to a non-purebred cock, would have visible evidence of the dark-egg genes in only with half of her descendants.

This could explain the impression of a greater effectiveness of the cocks to transmit the characteristic of dark eggs in the first generation.

Attention must be paid as this situation is indeed misleading; it describes only one coupling of subjects which one can suppose non-purebred, at least to some extent, for genes related to the characteristic of “brown eggs.” With time, the recessive brown egg genes will reappear.


A rule exists, strictly mathematical and undeniable:

If one mates a cock that is 100% pure for the dark brown egg genes with a hen quite as pure for these same genes, one will always obtain 100% of pure offspring; but if the transmission is quite as influenced by either the cock or the hen, it is not important whether the genes are known as “sex-linked” or “autosomal.”

spotted eggs


With this complexity of the genetic factors for “brown eggs,” one then understands much better why crossings with breeds other than purebred Marans can cause the loss of the characteristic “extra-russet-red eggs” in their descendants, especially in the first generation, which then makes from there the transmission of the dark egg genes very hazardous to the point of discouragement to even the boldest stockbreeder.

To better convince some, we can point out here the experiment which was undertaken in the years 1967-68 by crossing Russian hens with our Marans with disastrous results, which obliged, in the final analysis, to reverse this unfortunate initiative.

It is to be noted that currently certain professional hatcheries state they sell “Marans poultry,” which have nothing to do with our purebred Marans since theirs always disappoint when they produce barely tinted eggs! These chickens also lack other characteristics that should be present in the phenotype of the Marans.

We repeat that any crossing “outside of the breed” of the Marans is to be categorically proscribed.



The extra-russet-red colour comes from the impregnation of a liquid colouring on the eggshell. This liquid is produced by spongy tissues of the last 10 centimetres of the oviduct and is deposited right before laying.

Immediately after laying, a layer of mucus covering the egg dries quickly and the shell keeps its colour.
It is these many mucous glands that secrete the colouring substances and tint the shell.

These substances of albuminous origin are manufactured by certain cells whose biochemical laws to date are not elucidated.

On an egg just laid and still wet, one can damage whole or part of this coloured film with one’s finger. An unhappy experiment for a hen whose egg had remained blocked in the oviduct for several days had made it possible to note that the successive layers of pigment had not ceased accumulating and formed a film in the range of 1 mm in thickness and an almost black purplish colour.

Contrary to the blue-green egg of the Araucana hen which is tinted throughout the thickness of the shell, one realizes when one breaks a Marans egg that the internal colour of the shell is perfectly white, offering an unexpected contrast, and given its colouring right before laying, is like a final signature suitable for the breed.


“An identity card”

The deposition of the pigments on eggs is not always uniform.
With the manner of a print, like a child practicing with a wet sponge soaked in colour, one observes variation in the distribution of the pigments that are unique to each layer.

The shell is uniform when the print is perfectly carried out, allowing a homogeneous diffusion of pigment over the totality of the egg. Quite as frequent as the uniformly pigmented egg is the appearance of fine networks of dots some tenth of a millimeter in size spread over a clearer background. Occasionally there can appear very brown spots, in slight relief, on a clearer or definitely more constant background.

However, these deposits of pigments are not only subjected to variations from one hen to another but also in respect to time. Observations made with trap-nests over 15 years of breeding enabled us to note in the best extra-russet-red egg layers that aspects of the shell established at the beginning of laying continue, with some variations, to some extent allotting “an identity card” for each hen.

One can thus determine 3 categories of eggshell types in the Marans:

- uniform
- stippled
- spotted

One cannot judge the final qualities of a layer for extra-russet-red egg colour until one dozen eggs have been laid, counted from the first onset of laying. These nuances then deteriorate very gradually until the sixth month of laying.

At that time the best hens lay eggs certainly less characteristically dark but still more deeply coloured than those of other breeds.

It is also noted that in a series of 3, 4, and 5 eggs laid in continuation after a one-day stop, the first egg laid is always more deeply coloured.

This decline in colour intensity, and the cessation of laying during the incubation, in fact marks a natural and necessary rest of the oviduct common to all breeds

As with a hen’s first egg, after a period of broodiness, of incubation or moult good layers again start to lay a superb extra-russet-red egg.


External influences on egg colour:

It is significant to announce that poor sanitary conditions can considerably influence the colour of the shells.

Before any quantitative drop in production occurs, a decline in colouring, an abnormal distribution of the pigments, or the appearance of aspects which are whitish and rough are the advertisement of diseases or parasites.

Excessive fattening of the hens, changes of environment, of feeding, and stress factors are also prejudicial toward loss of eggshell colour.


The thickness of the shell:

In a general way, the solidity of the shell is closely related to the factors located upstream of the production of an egg: the bird’s genetic origin, the age of the layer, feeding, breeding conditions, and the bird’s medical state.

The shell represents approximately 10% of the weight of the egg. In the Marans, when these optimum conditions are met, one notes that the solidity of the shell is greater than that of eggs of other breeds.

Even when the empirical observation is easy (when one breaks a Marans egg, it is often with a certain difficulty), no scientific proof had attested it until a group of students (promotion 1995-1997) of the Institute des Sciences et Vie de la Terre (I.S.V.T.) of Puy en Velay studied the extra-russet-red eggs of the Marans.

According to measurements and calculations carried out, we could highlight which Marans hen’s eggs had a more solid shell than that of traditional eggs.

These would thus have considerable advantages for marketing, decreasing the number of potential breakages during transport, and the storage time of these eggs is quite longer than that of traditional eggs.

The thickness and the solidity of the eggshell of the Marans is now scientifically shown.

It is precisely the thickness of this less porous shell with a fine and tight grain which, but decreasing the gaseous exchange, avoids the oxidation of its contents: the air penetrates with difficulty into the egg and its conservation is somewhat prolonged.

This lower permeability often causes decreased hatchability of approximately 5 to 10% compared to majority of other breeds.


The shape of the egg:

The shape of the egg is an inherited feature that often enters in correlation with the extra-russet-red colour of the eggs.

In the best stock, one often notes a globulous form for which it its sometimes difficult to distinguish the point from the base; a distinction, however, necessary for the correct placement of the egg point down in the racks of forced-air incubators.

This characteristic of an almost spherical rather than ovoid shape is to be sought because all the old writings and testimonies describe this phenomenon. Probably, the genes responsible for this characteristic are incompletely dominant.

The cuticle and internal and external shell membranes of the Marans egg constitute effective protective barriers against bacteria.


The chemical composition of the egg:


A significant chapter has been opened in the past 2 or 3 decades since it had been claimed that the Marans eggs were richer in proteins and without cholesterol.

This propaganda had enough merit to interest the students of the I.S.V.T. in performing a chemical analysis of these eggs using electrophoresis for qualitative proportioning and Gornall’s method for quantitative proportioning.



Proportions of proteins

We have, thanks to electrophoresis, identified the three principal proteins of the egg whites of the Marans.

However, no protein specific to the Marans egg was revealed as had been announced in the book “Pêle-mêle d'expériences d'élevage…”, but it would have been necessary to make a more precise analysis to discover this specific protein.

It would be, in any case, a minor proportion because it was undetectable through electrophoresis.


Proportions of proteins in the egg white:

One realizes, within this proportioning, there are fewer proteins in the egg white of a Marans egg ( 93.02 g/L ) that in those of traditional hens ( 105.68 g/L ).
However, the previous assertions let us think that there was twice the quantity of proteins.


Proportions of proteins in the egg yolk:

Apparently the yolk of the Marans egg is slightly richer in proteins. However, with a more significant sampling we could have better assessed this difference.


Proportions of the lipidic phase:

The percentage of the total lipidic fraction of the Marans egg on average seems to be slightly higher than that of the eggs of traditional hens, although the variations were reversed for certain samples. We can therefore think that the differences observed are not inevitably significant.



The cholesterol level would appear slightly higher than average for Marans eggs. But the disparity of the results between each sample does not make it possible to show an obvious difference. In any case, it is possible for us to correct the previous assertions concerning the absence or low content of cholesterol of Marans eggs.

(Sources B.T.S. Anabiotec I.S.V.T.)



uniform egg of the Marans


In waiting for results of further analyses, we can nevertheless retain the principle that, if a protein specific to the Marans egg exists, it is in any event in infinitesimal proportioning.


But especially:

1-The colouring of the shell does not depend, in any case, on unspecified food factors or a particular soil. It is related only to the presence or absence of essential genetic factors.
2-The total quantity of proteins contained in the Marans egg is in no case higher than that of a traditional egg.
3-The advantages related to the extra-russet-red colour of the shell, with its greater thickness, its shape, and weight of the egg from 70 to 80 grams of adult hens, and the advantages real and inherent in the breed, already symbolize fundamental and quite sufficient identity.
4-In addition, the yolk is often firmer: placed on a flat surface it spreads out less and has a rounder form than a traditional farm egg.
5-If the Marans egg is better for certain, it is because it benefits from its “natural” packing and “top-of-the-line” protection that keeps it fresh longer and allows it to travel better than other eggs.



The MCF colours scale for the Marans eggs, numbered from 1 to 9, starts from a white egg ranging to highly-coloured, extra-red (violet black) eggs produced by exceptionally slow progress through the oviduct.

The Official Colours Scale from 1 to 9:

Echelle des couleurs des oeufs de 1 à 9


Photos sous licence Creative Commons
type CC by sa

Legend :

1 - White egg : example : Bresse-Gallic or Leghorn, Campine, Ancona, Braeckel for foreign breeds. Unacceptable.

2 - Tinted egg : Wrongly called “brown” in most of the foreign breeds standards as for instance the Rhode-Island Red. As well, it is the colour of eggs from numerous industrial hybrid stocks, never laid by a pure-bred Marans. Unacceptable.

3- Red egg : it’s could be a Marans egg but it’s an unsatisfying colour and lacks brightness. The colour is insufficient when it’s the darkest egg laid, usual in the stock which didn’t show any occasional superior specimens.

4- The real extra-red Marans egg

The colour of the egg is not better than the egg n°3, but the pigments quantity is more significant, its stained repartition is uneven, and that’s why the extra-red egg is more valuable. A little brightness should always highlight this egg. The egg n°4, placed on a natural red earthenware bottom, has to be a bit darker.

Note : the same hen can lay an egg that is slightly darker with an even colour in the beginning of the laying (first 20 eggs).

5 to 9 – Extra dark russet-red egg (chocolate)

You may notice the spherical, globular shape which is typical to the Marans egg, and the brightness is always an extra property for this egg. Unfortunately,  hens laying eggs 7, 8 and 9   often do not meet the standard for appearance: they maybe  light or skimpy subjects, have squirrel tails, impure feathers and colours, etc…  The selection of the Marans is a very hard work and a long exacting task.

8 and 9 – Exceptional eggs or rather accidental : the colour is close to that of an unalloyed pigment. Once again, you may notice that such eggs are obtained in the beginning of the lay. The fact that the shells pigments tones down in the middle of the laying period is normal. The best shell colours stabilize around 6 and 7. A good stock can produce an  proportion of eggs 5 and 6. Drastic selection must be done years after years to maintain a constant colour.

You can value the quality of a laying hen according to the colour of the eggs at the beginning of the lay after the first 20 eggs and the regularity of the colour during the greater part of the season.

Translated from French by: Katherine Anderson

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