Causes of infertile chicken eggs

Even though it’s not much
fun, I autopsy all of the eggs that don’t
hatch after 23 or 24 days.  At first, I found lots of partially or
fully formed chicks during my post-hatch autopsies, but as I got better
at incubating, more and more of the eggs that didn’t hatch were simply
full of liquid and no chicks.  Of the 24 eggs we stuck in the
incubator at the end of July, 14 hatched, 2 were nearly fully formed
but died in the shell, and 8 showed no sign of chicks at all.



Chickless eggs can have
several causes.  First, it’s quite possible that the eggs were
never fertilized, especially since my later hatches occurred long after
the peak egg fertility period.  The chart below, which I mocked up
using data from The
Dollar Hen, shows
that hatch rate (and, presumably, egg fertility) follows the seasons,
with lows in July and August and again throughout the winter.  To
get the most  bang for your buck, you might choose to order eggs
during the peak fertility period in middle to late spring.



Another cause for chickless
eggs is embryos that died within the first few days of
incubation.  If you’re very astute, you might see spots of blood
in these eggs, signaling that the egg was fertilized and that a
miniscule chick started to grow.  You have to expect a certain
number of eggs like this when ordering
eggs through the mail
since longer storage, rough handling, and temperature extremes before
the egg goes into the incubator can all kill your chick before it
really begins to grow.  If you see lots of chickless eggs from
homegrown eggs, you should instead consider the viability of the
parents — are they healthy, on pasture, and young; do you have the
right number of hens per rooster; is the flock suitably outbred, etc.?



I ran across one final
tidbit while researching infertile (or seemingly infertile) eggs —
your hatch rate will probably correspond to the apparent fertility rate
of the eggs.  For example, since 67% of our eggs from the last
hatch had some signs of chick development, we should have hatched only
67% of the fertile eggs (11 chicks.)  Many of the factors that
cause embryos to die very young also make the surviving chicks weaker
and unable to survive all the way to hatching.  So I guess we got
lucky hatching out 88% of our fertile eggs into perky chicks.