The experiment consisted of 2 identical trials, conducted
1 wk after each other, with hatching eggs from
the same commercial Cobb 500 broiler breeder flock.
The breeder flock was aged 33 and 34 wk when eggs
were obtained for trial 1 and 2, respectively. Eggs were
stored for 6 d in trial 1 and 5 d in trial 2, and then incubated
for 17 d in a multi-stage incubator (Petersime
NV, Zulte, Belgium) at a constant machine temperature
of 37.6°C and relative humidity of 53%. Eggs were
placed in a vertical egg position with the air cell up,
and turned hourly at an angle of 90°. After candling at
embryo day (E) 17 (after 416 h of incubation), fertile
eggs were collected from 1 setter trolley, weighed, and
only eggs in the range of 51 to 56 g were transferred to
a Plexiglas hatching cabinet (1.2 × 2.3 m), which provided
room for 3 setter trays. Per trial, 300 eggs were
randomly distributed over 3 setter trays (100 eggs per
tray). Per tray, all eggs were placed in the same position,
which was (1) vertical with the air cell up (ACU);
(2) vertical with the air cell down (ACD); or (3) horizontal
(HOR). The setter trays were placed next to
each other in the hatching cabinet, about 30 cm above
the floor of the cabinet, which was covered by wood
shavings. The position of the egg trays in relation to
one another was changed between the trials.
From E17 to E21.5, eggs were not turned, the set
point of the air temperature remained constant at
35.0°C, and air speed was lower than 0.2 m/s, which is
considered still air (Simmons et al., 2003). These conditions
were based on set points commonly applied in the
Patio system, and were shown to result in the highest
hatchability in our preliminary (unpublished) trials.