Because of the crowding, movement by one hen necessitates a major
disturbance to all in a cage. Since the hens cannot exercise, there is
a high prevalence of broken bones due to osteoporosis and a condition
known as cage-layer fatigue. The constant contact with bare wire
results in damage to the chickens' feet, which is also painful. The
crowding and lack of stimulation in these cages results in destructive
pecking, so the birds are debeaked. There is a high mortality rate in
the battery cage system which may be as much as one per cent per week.
Hens normally go through periodic molts during which they replace their
feathers. During molt, the hens do not produce eggs. If they were
allowed to molt naturally, it would be a problem for the producer
because it would be erratic. So after about a year of production, the
hens are forced to molt. This is done by keeping the shed in total darkness,
withholding water for up to three days and food for up to ten days. The
severe shock of this procedure results in rapid and simultaneous loss
of feathers.
Generally, after a second period of laying, the birds are
pulled from their cages and taken to slaughter. There are no laws
governing how birds are handled or transported nor how they are
slaughtered. In their weakened condition, many suffer broken bones from
rough handling. They are stuffed in crates, exposed to adverse weather
and finally slaughtered, often while conscious to some degree.
Many of these problems occur in cage-free egg production as well, but battery cages represent the worst possible treatment for hens. Hens have very strong behavioral traits which are denied expression
under these conditions. Wing flapping and stretching, flying,
scratching, dust bathing, perching, meaningful socialization, preening
and the use of a nest for laying are impossible in small cages.
More information on battery cages:
Wikipedia
HSUS No Battery Egg Campaign, including Cage Free vs. Battery Cages
COK and HSUS Expert Statements


