The first peak of embryo mortality (fourth day) occurs when the
majority of structures are being formed (Fig. 6-7). There may also be
abnormalities at this time due to an irregular number of chromosomes.
This first peak is usually followed by a long period of low mortality.
Deficiency of certain nutritional ingredients can cause a mid-
peak of mortality (twelfth day) comparable to that of the first peak.
The third peak (twenty-second day) is associated with hatching prob-
lems. On the twenty-first day, the embryo has its head between its
thighs and there still is an external yolk sac and a little remaining
albumen.
During the last three days, the embryo gets its head under its
right wing and picks into the air cell then pips in a counter clockwise
direction. With pipping, pulmonary respiration begins. The allantois
regresses at this time and the yolk is brought in through the yolk sac's
umbilicus. When the chick pips, all the albumen should have been
utilized as it can stick against the nostrils and cause asphyxiation.
Asphyxiation can also result from excessive humidity if moisture en-
ters the chick's nostrils as it pips.