I’m thinking about feeding
our chickens more homegrown seeds this year, so I decided I’d better
look into the one safety issue — phytic acid (aka phytates). 
The Weston
Price Foundation
sums up the issue in a nutshell:

So, feeding your
chickens (or yourselves) lots of raw beans, seeds, nuts, and grains can
make them malnourished since they won’t be able to get the phosphorus,
calcium, zinc, and magnesium they need.  Luckily, there are
several possible solutions.

• Soak
  the seeds.  Especially with legumes, soaking the seeds at
  warm temperatures (140 degrees Fahrenheit is most effective) for up to
  36 hours can reduce the phytic acid content enough to double the
  nutrition you get from the seeds.  Just soaking for 18 hours at
  room temperature removed half to two thirds of the phytic acid from
  three kinds of beans.  This is much more effective than sprouting
  the seeds or cooking them.  See this
  blog for more information.
• Remove the seed coat. 
  Most of
  the phytic acid is found in the seed coat, so white flours and similar
  products are much safer in this respect.  Unfortunately, most of
  the
  nutrition in seeds is also found in the seed coat, so you should use
  this technique with caution.
  
• Grind seeds and soak the mash. 
  Traditionally, farmers used to grind grains and legumes into a mash
  which they soaked before feeding it to pigs and chickens. 
  (Ruminants don’t have as much trouble with phytic acid, so this wasn’t
  necessary when feeding cows, etc.)  This technique activates a
  protein called phytase, which is already found in the seeds (especially
  in rye) and which breaks down the troublesome phytic acid.  This
  is also part of the theory behind making sourdough bread.
• Choose seeds lower in phytic acid. 
  Unfortunately,
  the best sources of protein also seem to be the worst phytic acid
  offenders.  Soybeans, peanuts, almonds, and sunflower seeds have
  up to
  three times as much phytic acid as cowpeas (which seem to be one of the
  safer seeds.)  Grains tend to fall somewhere in the  middle.
• Grow our own seeds. 
  Phytic
  acid content within the same type of seed varies drastically depending
  on how the seeds were grown.  Some studies suggest that raising
  your
  seeds with compost instead of chemical fertilizer (especially high
  phosphate fertilizer) will reduce the phytic acid content. 
  Fresher seeds will also help since these seeds have more phytase to
  counteract the phytic acid.
• Increase vitamin C in the diet. 
  Ascorbic acid in the diet has been shown to counteract the effects of
  phytic acid, at least with regard to iron absorption.  So, if you
  feed
  your chickens a lot of fresh fruits and vegetables at all times rather
  than making seeds the entirety of their diets, the phytic acid won’t be
  as much of a problem.  In general, the more well-rounded your
  chickens’ diet is, the less difference a bit of phytic acid will make
  in their lives.

Does that sound
complicated enough to send you scurrying away from trying to make your
own chicken feed?  I hope not — after all, I suspect the big
feed companies don’t pay that much attention to phytic acid when they
mix their feeds.  Some scientists suggest that the high phosphorus
levels in chicken manure are the direct result of feeding chickens food
high in phytic acid which they can’t digest.  Surely we can do
better.