De lo que he leído abajo, se trata de un problema de desarrollo. Espero que ayude.

http://www.ardeola.org/pubs/37(1)/37-52?lang=es

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Note added at 25 mins (2009-01-31 22:56:18 GMT)
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Perdona que no funcione el link, puedes copiar/pegarlo. Parece que hay algún problema en el campo de los enlaces.

translated as this in ref below

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Note added at 33 mins (2009-01-31 23:04:24 GMT)
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http://www.ardeola.org/pubs/37(1)/37-52?lang=en
http://www.ardeola.org/pubs/37(1)/37-52?lang=es

Underfed, emaciated, growth-stunted chickens
golpeados - bruised chickens

http://vegforlife.org/VFLguide_June07.pdf
• Egg-laying hens are among the most
abused of all farm animals.
• On factory farms, four or more hens are
forced to live inside tiny wire enclosures
called battery cages. In these confines,
the hens are unable to stretch their wings
or legs, fulfill social needs or engage in
natural behaviors.
• Constantly rubbing against the wire of
battery cages, hens suffer severe feather
loss and are covered with bruises and
abrasions.
• To prevent injuries caused by excessive
pecking, a result of unnatural, overcrowded
conditions, chickens’ beaks are
seared off with a hot blade.
• In order to shock their bodies into another
egg-laying cycle when production
declines, the hens are denied food, water
and light for up to two weeks. This cruel
process is known as forced molting.
• Considered “spent” after egg production
declines, laying hens are typically
slaughtered after only one year in
production.

http://www.cabi.org/pdf/books/9781845932152/9781845932152.pd...
see page 19 where it speaks to constraining the growth of chickens.

HTH these help in someway.