April pointed me toward some
great information about deep bedding (aka deep litter) on Robert
Plamondon’s website. 
I had thought the main benefit of the system was for the garden,
capturing all of those nutrients in chicken manure that might otherwise
leach away, and later decided that deep
bedding also has the benefit of keeping your chickens warm in the winter.  But poultry
scientists from the 1940s turned up another major benefit — increased
chicken health.



When done correctly (more on how
to do that in a later post), deep bedding is a bit like compost — you
build up a community of beneficial microorganisms that keeps the
ecosystem running.  As readers of Teaming
with Microbes know,
a healthy soil food web cuts down on plant pathogens since the good
microorganisms are able to outcompete the bad.  A similar effect
may be taking place in deep litter, but in this case the good
microorganisms outcompete the protozoa that cause coccidiosis.  Meanwhile, low levels
of coccidiosis protazoa in the deep litter may act like a vaccination,
inoculating your chicks with low levels of the disease that their
immune systems can fight off and then become resistant to. 
However the specifics work, the poultry scientists showed that chicks
raised on well aged deep litter had a lower mortality rate than chicks
raised on young deep litter or without deep litter.



The scientists also found that
deep litter helped counteract the effects of a poor diet.  They
put one set of chickens on a vegetarian diet that they knew lacked
essential ingredients for avian health and another set of chickens on a
complete diet.  Some chickens from each group were raised on deep
bedding of various ages, and others were given fresh bedding
regularly.  Once again, the deep litter birds did better, with
growth rates and survival rates of malnourished birds on deep litter
nearly matching those of well nourished birds.  Once again, the
causes of deep litter’s effects on chicken health is unclear, although
I’ve read (and can come up with) a variety of possibilities. 
Robert Plamondon suggests that vitamin B12 is produced in the deep
litter through bacterial fermentation, while I wonder whether
microorganisms (like worms) attracted to the deep litter aren’t
scratched up by the chickens to supplement their diets.  I
wouldn’t be surprised if the chickens even ate fungi growing in the
deep bedding, getting some nutrition that way.



The authors concluded:

So, if you have to keep
your chickens confined (or if they confine themselves during cold
winters), deep litter is a great way to keep your flock brimming with
life.  And don’t forget to throw in a homemade chicken
waterer to complete
the health cure!