On some occasions, consumers can see blood in the chicken egg in the form of red spots. What is the explanation?

The chicken egg is one of the most nutritional foods in the world. Currently, 76.7 million tons of eggs are produced worldwide; it is widely consumed. Part of its nourishing power comes from the 3.5 grams of total protein in every 60g of the egg. In addition, has a high content of healthy fats and vitamins A and B.

Occasionally, consumers may see blood spots in the chicken egg on the yolk. To understand why these red spots appear, one must know the process of chicken egg formation.

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How is the chicken egg-formed?

The process of chicken egg formation is complex because it involves several anatomical regions.

At first, the egg yolks are formed. Then, yolks pass into the oviduct. The oviduct is divided into infundibulum, magnum, isthmus, uterus, and cloaca. At this stage, blood may remain in the yolk of the chicken egg.

In the infundibulum, the yolk is covered by the vitelline membrane for protection. Then, in the magnum, proteins are synthesized and deposited in the egg (egg-white). The albumen is 50% water and weighs 15g. After, in the isthmus, this albumen is covered by testaceous membranes.

The egg then passes into the uterus, where it rotates, and the yolk-supporting chalazas are attached. In addition, more proteins are deposited in the uterus. The formation of the shell is the longest stage of all, taking 23 hours. Finally, the egg rotates 180° in the cloaca and is expelled by the hen.

Generally, laying occurs between 7 and 11 am. After 15 to 30 minutes, ovulation begins, which will produce the next egg.

Stages of chicken egg formation

Table 1 Stages of hen egg formation according to anatomical region, physiological process, and duration. 

It is estimated that blood in the chicken egg appears between 1 to 3% in white eggs. Meanwhile, this phenomenon seems to be more frequent in brown eggs, with 6%.

Causes of blood in the chicken egg

Generally, blood in the chicken egg is observed as red spots on the yolk.

Video: Presence of blood in chicken eggs

Blood in the chicken egg is caused by the rupture of one or more small blood vessels in the yolk at the time of ovulation. Human health organizations such as the Food Safety and Inspection Service (USDA) assure that there is no problem with the consumption of these eggs.

1. Normal egg formation: The appearance of blood in eggs is normal due to its formation. The eggs, when detached from the ovarian follicle, may break blood capillaries. These capillaries are small blood vessels and they are fragile. When the egg (yolk) detaches and capillaries break, blood is released and coagulates in the yolk. Therefore, red spots will be seen in the yolk.
2. Deficiency of vitamins A and K: Modern diets supplied to laying hens ensure a good nutrition. However, Vitamin A or Vitamin K deficiency may eventually occur. This problem has been associated with the rupture of capillaries, favoring the appearance of blood in the chicken egg. Some medications or mycotoxins can affect the function of these vitamins.
3. Biotin and magnesium deficiency: a poorly balanced diet can have deficiencies of biotin and magnesium. This nutrient deficiency can generate hemorrhages at the junction of the chalaza and the egg yolk.
4. Stress: Stress factors such as lack of water, poor quality or moldy feed, poor house hygiene, or noise affect the laying process. Sometimes, sudden changes in the lighting system or excessive light generate stress in the hens, which favors the blood in the chicken egg.
5. Fertilization? A popular belief is that these eggs are fertilized (have a developing embryo). This idea is false. First, in poultry farming, laying hens are not mixed with males. Second, the eggs are weighed and sometimes evaluated under light to see inside. Fertilized eggs are discarded, and they are not sold. Third, the management conditions in poultry houses prevent hens from hatching a fertilized egg correctly, even in backyard production.

If blood is present in the chicken egg, these stains can be removed with a spoon by the consumer. They do not represent any health problem.

Recommendations for egg consumption

The presence of blood in the chicken egg does not represent a health problem. However, there are other aspects related to the safe consumption of chicken eggs.

• Egg condition: Eggs for consumption should not have broken or contaminated shells. In addition, eggs should not be washed because it will damage the natural barrier of the shell. To know its freshness, raw eggs can be immersed in water, if it sinks indicates that it is fresh.
• Handling: the containers in which eggs are beaten or handled should be used only for this purpose and should not be used for other culinary processes. In addition, it is advisable to store eggs in a cool environment between 7 and 15°C.
• Do not consume raw eggs: The USDA recommends that raw eggs should not be consumed because of the risk of becoming infected with Salmonella Enteritidis. This advice applies especially to infants, young children, elder people, pregnant women, and people with weak immune systems.
• Cook eggs well: eggs should be cooked until the yolk is hard-boiled, either by scrambling, frying, or baking. If there is blood in the chicken egg, it can be simply removed with a spoon before cooking.

CONCLUSIONS

Blood in the chicken egg can sometimes be seen as red spots on the yolk. This rare phenomenon does not represent any problem for human health. Some causes favor the break of blood vessels in the ovarian follicle, releasing blood that coagulates in the yolk. On the other hand, there are other aspects to be considered regarding the consumption of chicken eggs.