3rd International Poultry Meat Congress

2) Effects of EST on later life performance
In case chicken quality at hatch will be affected by EST during incubation, it may be expected that
later life will be affected as well (Decuypere et al., 2001). Only a few studies have investigated
effects of incubation temperature during early incubation on later life performance. Joseph et
al. (2006) investigated effects of a low EST during the first 10 days of incubation (36.6 vs
37.8oC) and reared chickens till day 42 of age. Body weight at day 42 of rearing (3014 vs 3103
g) and percentage breast fillet (23.2 vs 23.7%) were lower in chickens incubated at the low EST
compared to the optimal EST.
More studies have been studying effects of high EST in late incubation on later life performance.
Hulet et al. (2007) were one of the first that demonstrated that a high EST (39.7oC from day 16
of incubation to hatch) resulted in a lower BW at day 44 of rearing than an EST of 38.6oC in
the given incubation period. Comparable results were found by Molenaar et al. (2011a). They
exposed eggs to an EST of 37.8oC or 38.9oC between day 7 of incubation and hatch and reared
chickens thereafter till 42 days of age. Chickens incubated at 38.9oC had a lower body weight at
day 42 (2854 vs 2895 g), had a non-significant higher FCR (1.93 vs 1.91) and a higher mortality
rate during rearing (12.5 vs 8.4%). When reasons for mortality were investigated, the difference
in mortality between both incubation temperatures could be attributed to ascites (6.6 vs 2.8%).
3) Proposed mechanism involved in effects of high incubation temperature on chicken
quality, growth performance and metabolic disorders
Based on the results indicated above, it can be concluded that particularly during late incubation
a slightly higher EST than optimal results in lower chicken quality at hatch and impaired rearing
results in later life. Although not all details are clear yet, the physiological mechanism involved
becomes more and more clear. The hypothesized mechanism will be discussed below, with the
focus on high incubation temperatures during late incubation.
Because the chicken embryo during late incubation acts as a poikilotherm, the body temperature
and the metabolic rate depends on the EST (Lourens et al., 2006b). A high EST results in a high
metabolic rate, meaning that more nutrients are required. Particularly, the glucose requirements
for metabolism are increased (Molenaar et al., 2013). Because glucose storage in fresh eggs is
very limited (