Abstract
1. It has been reported that the increasing CO2 tension triggers the embryo to pip the air cell and emerge from the egg. However, the mechanism by which higher CO2 concentrations during the last few days of incubation affect chick physiology and the hatching process is unclear. This study investigated the effect of CO2 concentrations up to 1% during pipping, on the onset and length of the hatch window (HW) and chick quality.2. Four batches of Ross 308 broiler eggs (600 eggs per batch) were incubated in two small-scale custom-built incubators (Petersime NV). During the final 3 d of incubation, control eggs were exposed to a lower CO2 concentration (0.3%), while the test eggs experienced a higher CO2 concentration programme (peak of 1%).3. There were no significant differences in blood values, organ weight and body weight. There was also no difference in hatchability between control and test groups. However, a small increase in the chick weight and the percentage of first class chicks was found in the test groups. Furthermore, plasma corticosterone profiles during hatching were altered in embryos exposed to higher CO2; however, they dropped to normal levels at d 21 of incubation. Importantly, the hatching process was delayed and synchronised in the test group, resulting in a narrowed HW which was 2.7 h shorter and 5.3 h later than the control group.4. These results showed that exposing chicks to 1% CO2 concentration during pipping did not have negative impacts on physiological status of newly hatched chicks. In addition, it may have a significant impact on the physiological mechanisms controlling hatching and have benefits for the health and welfare of chickens by reducing the waiting time after hatching.
Highlights
There is a large variation in eggshell conductance within a batch of chicken eggs, resulting in a large variation in gas exchange, and this creates differences in hatching time which can be further increased by differences in storage time, egg size, breeder flock age, and incubation conditions
That air cell and blood gas pressures are altered by exposing embryos to high CO2 during the first and second weeks of incubation
Environmental hypercapnia results in an increased blood pCO2, blood pH and HCO3- concentration in avian embryos (Bruggeman et al, 2007; Everaert et al, 2008; Everaert et al, 2011).the significant increase of pCO2 by higher environmental CO2 concentrations were not found in this study
Summary
There is a large variation in eggshell conductance within a batch of chicken eggs, resulting in a large variation in gas exchange, and this creates differences in hatching time which can be further increased by differences in storage time, egg size, breeder flock age, and incubation conditions. A number of events are known to be required to initiate the hatching process in chickens One of these is a change in the levels of O2 and CO2.With increasing metabolism and limited conductance of the eggshell (Hamidu et al, 2007), in a natural nest the CO2 level increases from 0.05 to 0.90% (Boutilier et al, 1977; Buys et al, 1998),while the O2 concentration declines from 20.9 to 20.3% (Walsberg, 1980). The alteration of CO2 levels during late incubation has not been well investigated in relation to hatching. It is questionable how it affects hatchability and chick quality.
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