Egg position did not affect BW, yolk weight, or
YFBM. The Pasgar score was highest in chicks hatched
from ACU eggs, and lowest in chicks hatched from ACD
eggs. The incidence of poor navel quality was highest
in chicks from ACD eggs, followed by chicks from HOR
eggs. In the current experiment, after emergence from
the eggs, chicks had to crawl away from the egg and fall
down through openings in the setter trays onto the litter.
Chicks that hatched from ACD eggs emerged from
the egg at the region of the air cell, facing the floor of
the hatching cabinet. Possibly, remnants of the chorioallantoic
arteries were torn as the chick fell down directly
after it fractured the eggshell, thereby increasing
the risk for unhealed navels and leaving a small scab of
blood, which is the most common type of unhealed navel
(Fasenko and O’Dea, 2008). High incidences of red
hocks and red beaks in chicks from ACD eggs also point
at a demanding hatching process. The length of chicks
from ACD eggs was 1 to 2 mm shorter in comparison
to chicks from the other egg positions. It must be noted
that although differences in Pasgar score and chick
length were statistically significant, they are small and
relevance of these differences for later life is not clear.
Interestingly, despite equal initial egg weights, both
body and yolk weights of chicks in trial 1 were 0.5 and
1.0 g lower, respectively, than in trial 2, whereas the
YFBM was 0.6 g higher. These data point in the same
direction as the earlier hatching time in trial 2, and suggest
a higher incubation temperature from E0 to E16
for eggs in trial 2, as higher temperatures lead to lower
YFBM and higher yolk weights at hatch (Molenaar et
al., 2010). The Pasgar score was lower in trial 2 due to
an increase in red hock incidence in chicks from each of
the egg positions. Red hocks were associated with prolonged
pushing of the hocks against the eggshell during
the hatching process (Wilson, 2004). However, both the
IP-EP interval and the EP-hatch interval were about
1 h shorter in trial 2 than in trial 1; thus, it seems unlikely
that prolonged pushing of the hocks against the
eggshell was the cause of the increased red hock incidence
in trial 2. If the temperature from E0 to E16 was
higher in trial 2, as suggested by the earlier hatching
time and lower YFBM, then possibly the metabolism
was increased in these embryos, and thereby the CO2
pressure in the air cell at the end of incubation, stimulating
the time of pipping (Visschedijk, 1968). Thus,
these embryos may have been struggling more for quick
access to the air cell and penetration of the eggshell,
thereby pushing the hocks against the eggshell.
It is concluded that egg position in the last 4 d of
incubation does not affect hatchability, but seems to
affect the duration of the hatching process and chick
quality.