There is, if you believe the literature, a lot of reasons for having what is commonly referred to as Dead in Shell. This is where the chick starts to develop, but at some point during the incubation cycle the chick dies. If the egg never develops this is NOT an instance of Dead in Shell but probably a clear/unfertilised egg. Dead in Shell does not include chicks that die after separation from the shell.

Some of the “so called” reasons for Dead in Shell are:
  • Too much humidity.
  • Too little humidity.
  • Bacterial infection.
  • Fungal infection.
  • Viral infection.
  • The Hen leaves the nest and allows the eggs to cool.
  • Thunderstorms causing the chick to die.
  • Poor nutrition of the Hen.
  • Too much calcium in the Hens diet which makes the shell too hard for the chick to crack.
With a list like that it’s a wonder we ever have live chicks. Well the reality is that most of the time and without taking any precautionary measures, Dead in Shell will occur in very few nests.
To look further, the shell is a porous membrane that is full of small holes that allows moisture, the exchange of gases and also bacteria etc. to pass through the shell, and if you do have ill birds or a very dry season, bacteria or humidity could play a part in the problem.

If your experiencing a lot of Dead in Shell (more than 1 in 12 fail to hatch), then it may be worth having an egg tested by a Vet or attempt to determine when the chicks development stopped. You can, by using a light source, periodically check the eggs to see that they are developing at the correct rate. By holding the egg up to a strong light you can see the development of the chick as follows:

3 – 4 days - blood vessels are just visible.
5 – 8 days - egg darkens and takes up most of the space, this gradually increases each day.
9 –13 days - the egg should be completely dark except for the air sac, which should remain unchanged in size. If the air sac increases or shell becomes dull, grey it suggests a dead embryo.

“When you have a Dead in Shell, carefully open the egg on the end that has the air cell. A small membrane separates the embryo from the air cell. If this membrane has not been broken, the death is most likely caused by the egg being chilled early in the incubation process. The first trimester is the most critical period. An egg chilled during this time will often continue to develop, but will fail to break into the air cell and will die without hatching (late death). Chilling in the third trimester often does not affect hatch.”(1)

When examining the dead chick, if it appears to be stuck to the inside of the shell, the problem is too little humidity. The chick will be stuck to the shell of the egg and will be unable to rotate or move to break the shell and subsequently dies.
Most bacterial, viral and fungal deaths will occur in the first 7 days and will be observed as the embryo only partially developed.

If you get a high number of Dead in Shell then review the cleanliness of your cages and eliminate any obvious causes of disease and/or something that may be disturbing the hens, like a Cat or Mice. If you think that it is a lack of humidity get a bottle sprayer for water and on about the 11th day give the eggs and the hen a light spray.

1 “Diagnosing Dead in Shell” by Carol Heesen & John Wilson (1999)
2 “Incubation Problems” University of Illinois (2004)
3 (2000)

Author: Peter Ailwood - Published 2/11/04