Juan Carlos López

Content available in: Español (Spanish)

Opening of unhatched eggs remaining on the tray and the assessment of lesions or abnormalities in the rejected fowls during hatching are a significant tool which allows to evaluate the management and conditions fertile eggs were exposed to during a certain period of time.

Mortality occurs during every embryonic stage of development. What is important is to be able to establish what is “normal”, and in case something is not, to be able to determine the cause(s) at that time.

Embryo diagnoses must be routinely performed, and not only when problems arise.

Those very trays where embryo diagnosis is performed must be monitored for water loss upon transfer, hatching window and weight of the chick with respect to the initial weight of the egg.

The chances of being able to spot the cause of the problem are increased when the findings upon opening the eggs are related to the above monitored parameters.

A few cases found in incubation plants, which can be useful to understand future abnormal embryo mortality in our plants are shown next.


In this case, an abnormal increase of dead embryos was observed in the first two days of incubation, as well as a high percentage of weak shells and an intermediate increase of contamination-related mortality.


  • Considerable rise in very early embryo mortality (day 1) Photographs 1 and 2
  • Increase in the percentage of weak white shells and contamination Photograph 3
  • Mottled yolks Photograph 4
  • Increase in intermediate mortality  due to contamination Photograph 5

Photograph 1. Fertile, dead before incubation


Photograph 2. Dead on day 1-2 of incubationfoto-3

Photograph 3. Weak shells


Photograph 4. Mottled yolks


Photograph 5. Contamination

There were no changes in the way eggs were handled in the farm -collection, spraying, storage temperature, or transportation

Possible Causes

  1. Infrequent collection
  2. Prolonged and/or inappropriate storage
  3. Prolonged pre-incubation
  4. Excessive spraying
  5. Severe nutritional deficiencies
  6. Incorrect transportation
  7. Temperature too high or too low during the first days of incubation
  8. Lack of egg turning
  9. Ocratoxins and T2


In this case, early mortality was the result of a severe stress situation (earthquake): mottled yolks (disturbance of the vitelline membrane)  were the evidence.

Weak shells, some of them fissured, which lead to contamination, were the result of the stress caused by oviposition before the shell was completed, or an abnormal retention of the egg in the egg formation gland, which resulted in subsequent eggs not having enough time to develop properly.


In this case the existence of an abnormal percentage of red hocks and pipped eggs were observed, as well as the presence of umbilical cords (“navel strings”).


  • Increase in the percentage of chicks with dehydrated legs and “red hocks” Photograph 6
  • Eggs laid by pullets in their first few weeks laying.
  • Normal hatching window.
  • Water loss upon transfer (8%).
  • Eggs remaining on tray show pipping.
  • Rise in the percentage of chicks having navel strings.

Photograph 6. Red elbows


Photograph 7. umbilical cords

Possible causes

  1. Humidity too high during incubation
  2. High temperature during incubation
  3. Low temperature during incubation
  4. Vitamin deficiency
  5. Changes in the makeup of the shell


In this case the cause was the excessive moisture in the incubator and hatchery. The high amount of pipped eggs, along with the presence of umbilical cords confirms the diagnosis – Photograph 7

Usually, when the temperature is low the hatching is delayed. A high temperature leads to red elbows, splayed legs and crooked toes, and the hatching window shows an acceleration of embryonic development.


In this case, the existence of a high percentage of chicks with navel issues, such as black buttons, navel strings, and omphalitis.


  • Increase in the percentage of rejected chicks during hatching due to navel issues.
  • White feathers and lethargic chicks.
  • Eggs incubated in multiple load machines.

Photograph 8. Black button navels


Photograph 9. Omphallitis

Possible causes

  1. High humidity in the hatchery
  2. High temperature during the last week in incubators and hatchery
  3. Low temperature
  4. “Omphallitis” contamination


  • The  cause varies depending on the type of lesion.
  • Black button navelsPhotograph 8– are the consequence of a high temperature during incubation.
  • Starting from the second week the embryo’s temperature measured at the shell was 38.3ºC (100.9ºF) – 38.9 ºC (102ºF).
  • High temperature affects the thyroidIGF1-GH hormonal axis, which controls growth and chondrocyte differentiation; it lowers the expression of type X collagen and the transformer growth factor beta, two major proteins involved in  ossification.
  • In addition, high temperature accelerates embryonic developement, thereby demanding a greater consumption of oxygen, which can passively enter through the shell pores; the embryo exchanges energy from the yolk lipid metabolism, which demands oxygen due to the glycogen stored in the embryonic muscles. This process can result in an accumulation of lactic acid and muscle fatigue.
  • Lack of absorption of the yolk influences the utilization of critical nutrients for the early development and shaping of bones.
  • Poorly closed navels are generally due to a low incubation temperature. The “navel strings” are due to high humidity in the hatchery, which prevents the blood vessel to naturally dry out and come apart.
  • Omphallitis should be distinguished from the previously mentioned navel issues. Omphallitis-Photograph 9- is an inflammatory process, resulting from an infection.

The scheme below summarizes how temperature affects bone and tendon formation and causes the yolk sac not to be used correctly, because due to its greater volume, it is unable to completely retract into the abdominal cavity, which causes a portion of it to remain on the outside, becoming what is known as “black button”.




In this case, a reduced hatchability, pipped eggs, chicks with shells on their feathers, and excess fluff on hatcher doors were observed.


  • Significant drop in the hatchabillty due to a significant increase of pipped eggs – Photographs 10 and 11
  • Chicks with shells attached to feathers – Photograph 12
  • Copious amount of down attached to the hatchery gate – Photograph 13

Photograph 10. Pecked egg


Photograph 11. Pecked egg


Photograph 12  Chick with shell attached to feathers


Photograph 13. Down attached to hatchery gate

Possible causes

  1. Prolonged storage
  2. Unsuitable temperatures; low within the incubator and high in the hatcher
  3. Incorrect ventilation in hatcher
  4. No turning
  5. Upside down positioning
  6. Low humidity in incubator and/or hatcher
  7. Porous or fissured shells


In this case, several factors had an impact:

  • Eggs were kept in storage for 18 days.
  • The temperature within the incubator was low.
  • A rail for an additional row of eggs was used with a different eggshell conductance and for larger chicks.
  • The humidity inside the hatchery was too low.
  • Usually, when humidity is too high, we observe wet chicks covered with albumen, or fully developed chicks that don’t pip.
  • The  fowl to egg ratio shows a low weight loss.


In this instance we found a high mortality rate in the farm; the chicks had lost their apetite, they were lethargic due to yolk sac issues and chick motricity.


  • High mortality rate in the first 7 days in the farm.
  • Death resulted from small chicks with large yolk sacs.
  • Organs did not have lesions exhibiting bacterial contamination.
  • Chicks exhibited a lack of appetite and lethargy upon their arrival at the farm.

Photograph 14. High temperature during the last week in the incubator and hatchery

Possible causes

  1. High temperature over the last period in the incubator (above 38.3ºC/101.3ºF at the eggshell) and in the hatchery (chicks having rectal temperatures above 40.6 ºC/ 105.08ºF)
  2. Chicks subjected to low temperatures during the waiting period at the plant and/or during transportation (rectal temperatures lower than 39.4 ºC/ 102.9ºF)
  3. High carbon dioxide levels in the hatcher (over 7,000 ppm) and upon reception at the farm (over 2,500 ppm)

Photograph 15. Fowl with a 20% yolk sac ratio


Photograph 16. Fowl with an 8% yolk sac ratio


Photograph 17. Upside down chick


In this case, the temperature during the last week in the incubator and hatcher was too high – Photograph 14 -.

That high temperature affected the absorption of the yolk sac. Chicks with large yolk sacs do not have the need to search for food.

In addition, high temperatures affect the leg bone formation and hence, motricity.

Photograph 15 shows chicks with a yolk sac ratio of 20% in contrast with Photograph 16, which shows fowls with 8% yolk sacs.

The high levels of carbon dioxide and high temperature upon reception can generate “upside down chicks” Photograph 17

The blood samples from affected chicks show high levels of lactic acid and low glucose. Glucose is essential for the brain. Due to the low glucose level the stored glycogen is used, thus generating a great oxygen demand. When there is not enough oxygen available, lactic acid is produced, which is extremely irritant for the chicks’ nervous system.

This situation is more frequent in eggs from the first laying week, since the eggshell is thicker, which makes oxygen diffusion difficult.

The table below can be used as a guideline for assessing cracking in broiler chickens (Tullett 2009).






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