Exploration of eggshell color traits in brown eggshells
The epithelial tissue cells of the eggshell gland mucosa of the hen’s uterus undergo a series of physiological changes during laying and secrete two types of particles of different sizes. The large particles form the organic matrix proteins collagen and mucopolysaccharides, and the small particles are pigment granules containing protoporphyrin. These two types of granules increase in number until the cuticle is fully formed, with the pigment being secreted by the eggshell glands and deposited onto the cuticle 3-5 hours prior to egg laying.
Protoporphyrins are synthesized from glycine and succinyl coenzyme A, of which δ-amino-γ-ketoglutarate (ALA) synthetase is the rate-limiting enzyme Polin [4] found that porphyrins could be synthesized in vitro by incubating homogenized pieces of brown-shelled laying hens’ liver and uterine shell glands with δ-amino-γ-ketoglutarate (δ-ALA) for 24 h at 41°C, and the amount of porphyrin synthesized by the uterine shell glands was twice that of the liver, and the amount of porphyrin synthesized by the uterine shell glands was twice that of the liver, while the amount synthesized by the uterine shell glands was twice that of the liver. The amount synthesized by the uterine chitinous glands was twice that of the liver, whereas the other tissues synthesized only trace amounts of porphyrin in vitro.
The uterine tissue mass synthesized mainly uroporphyrins in vitro, with 91.4% of the porphyrins being uroporphyrins, 0.5% being faecal porphyrins, and 9.7% being protoporphyrins. In contrast, protoporphyrin type was extracted from intact uterus and eggshell, of which 97.1% was protoporphyrin and 2.9% was fecal porphyrin.Baird et al.[5] found that the shell gland cells were filled with mitochondria and their pH changed when eggshells were formed.
At the same time, the porphyrin content in the isthmus of the oviduct and chitin glands was three times higher during egg passage than in the absence of eggs. The change in the pH of the oviductal shell gland fluid during eggshell formation is an important factor in the secretion of pigments. Eggshell pigments are dissolved at low pH, and the pH rises again when the secretion of eggshell pigments is complete. At this stage, the abnormal change of local pH value will cause the uneven distribution of eggshell pigment on the surface of eggshell.
3 Excellent eggshell color is a sign of flock health, but disease and stress can cause eggshell color to deteriorate.
The color of brown eggshells is bright and uniform, which is a sign of flock health. Therefore, any factors affecting the health status of chickens, such as disease and stress, will lead to the deterioration of eggshell color. Once the brown eggshells are found to be lighter and whiter, unevenly pigmented and dull in color during the feeding process, it is a sign that the chickens are in the early stage of disease and stress or in the late stage of recovery.
When the virus bacteria or other toxic and harmful substances into the body of laying hens, it will cause edema and inflammation of the mucous membrane of the fallopian tube, or even hemorrhagic ulcers, the uterine shell gland pigment secretion cell dysfunction or loss, resulting in pigmentation is blocked, the eggshell white, spots, sand skin, thin shell, or worse, the egg white thin, egg weight reduction, lower egg production rate. The factors that affect the color of eggshells by damaging the health of chickens are mainly in the following three aspects:
3.1 Disease factors
Many infectious diseases, such as Newcastle disease, influenza, infectious bronchitis, egg-laying decline syndrome, etc., toxic diseases, such as mycotoxin poisoning, heavy metal poisoning, etc., can lead to brown-shelled laying hens with lighter eggshell color. After the occurrence of the above diseases in chickens, the oviducts become edematous, congested and hemorrhagic, resulting in necrosis and detachment of mucosal epithelial cells in severe cases, and partial or complete loss of the function of the eggshell glands to synthesize and secrete pigment [6].
In addition to causing clinical symptoms such as lightening and whitening of eggshell color, it is often accompanied by a sharp decrease in egg production rate, thinning of eggshells, shell-less eggs, and an increase in deformed eggs. Electron microscopic observation of pathological sections of ovaries and oviducts revealed that the secretory granules of the shell gland secretory cells were cavitated, mitochondria were edematous and lysed, and the cilia of the epithelial cells were greatly reduced, and some even disappeared completely.
Nutritional deficiency diseases, such as vitamin deficiencies and trace element deficiencies, can also cause poor eggshell coloring. Vitamins are involved in the metabolism of nutrients in the body. For brown shelled egg breeds, the vitamins that have a greater impact on eggshell color are vitamin A, vitamin E, vitamin K3, vitamin B6, vitamin B12, folic acid, niacin and so on.
Among them:
Vitamin A deficiency can cause the oviduct mucosal epithelium to be replaced by stratified squamous keratinized epithelium, leading to its malfunction.
Vitamin E during egg laying facilitates smooth shell surface and even distribution of shell pigmentation.
Vitamin K3 is involved in the synthesis of all types of proteins, especially hemoglobin, whose metabolites serve as raw materials for the synthesis of eggshell pigment.
Vitamin B6 deficiency causes atrophy of the oviducts and affects the synthesis of hemoglobin, immunoglobulin.
Vitamin B12 affects the development and maturation of red blood cells and the synthesis of the pigment protoporphyrin, thus affecting eggshell color.
Folic acid is the normal development of the immune system
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