Role of various zones of eggshell in gas exchange of
chicken embryo
O.I.STANISHEVSKAYA*
All-Russian Research Institute of Farm Animal Genetics and Breeding, St.Petersburg-Pushkin,
189620, Russia, *[email protected]
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Abstract
Gas exchange through various zones of eggshell was studied on chicken embryos (n=60).
During 9-19 days of incubation chambers (volume 1.6 cm3, S=1.5 cm2) were fixed with special
mastic on the equatorial zone, the zone of air cell and the zone of small end. Simultaneously the
general gas exchange was measured.
•
The intensity of gas exchange through various zones of eggshell changes depending on
the embryo’s age, and development of allantois. Since day 12th of embryogenesis the most
intensive gas exchange takes place in equatorial zone and zone between equator and small end.
•
Gas exchange in separate zones of eggshell surface as well as gas composition in air cell,
measured by puncture, do not reflect a reliable information of general gas exchange.
•
The CO2/O2 ratio in air cell zone and small end zone significantly differs during 13-19
days of incubation due to more intensive oxygen consumption through eggshell in small end
compared to opposite part of the egg and more intensive CO2 emission in air cell zone compared
to small end zone.
•
By traditional way of eggs loading into incubation trays the most important part of
eggshell surface becomes located in the most unfavorable conditions. This can play important
role for incubation efficiency of modern meat type crosses and breeds with high performance
and increased oxygen consumption.
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Keywords: egg shell; incubation; gas exchange; meat chicken
Introduction
Optimal conditions for gas exchange in chicken embryos are crucial for high levels of hatchability
and postnatal livability of chicks (Deeming et al., 1998). This is particularly important for embryos of
modern broiler strains and crosses, which are bred for outstanding breast meat output and need
sufficient oxygen supply during incubation (Boerjan, 2004). The conditions of gas exchange during
embryogenesis can influence on susceptibility of meat chicks to ascytes (Decuypere et al., 1995).
Though investigation of the gas exchange of chicken embryos has a long prehistory (the first data of
embryos breathing activity had been published by Boil in 1632), some aspects have not been clarified
until now. Namely- the role of different zones of eggshell surface in embryo gas exchange is
investigated not sufficiently. It is well known, that the pores on eggshell surface are located not
equally, on the small end zone their concentration is minimal and on the air cell zone- maximal. That
is why the air cell zone is considered as a most important part of eggshell surface, because the gas
penetration is here mostly active.
Our research work aimed to find out the role of various zones of eggshell surface in embryo gas
exchange depending on the age of embryos and general level of their gas exchange.
Materials and methods
The investigations have been carried out on the White Plymouth Rock embryos (n=60) during 9-19
days of their incubation before internal pecking. On the small end, equator and air cell zones of each
egg were glued down special chambers (V=1,6 cm3, S=1,5 cm2) for daily measurements of local gas
exchange. Simultaneously we measured total gas exchange with use of our original method. The
incubation eggs were placed into a hermetically closable vessel (V=250 cm3) for period from 1hour to
20 min. depending on the embryo’s age at the temperature of 37,6 0C. After that the changes of the 02
and CO2 concentrations in the chamber’s internal atmosphere were measured with use of mass
spectrometer MX 64-03 and received data were respectively re-calculated as ml/hour/embryo. The
changes in gas concentrations in the small chambers were measured with use of the same
spectrometer through small holes, hermetically sealable. Gas contents of egg air cells were measured
on day 19th of incubation by eggshell drilling.
2
5
Figure 1. Gas exchange of chicken embryos through various zones of eggshell surface on 13-14-15-18-19 days of
incubation (changes of O2 and CO2 concentrations during 1 hour inside attached chamber V=1,6 ml)
Results and discussion
We have found out, that gas exchange intensity on different sites of eggshell changes depending
upon embryos’ age and allantois development. During the investigated incubation period the most
active site of eggshell surface was middle equatorial part. This can be explained by the fact, that here
the allantois is developed best of all and is located close to eggshell. In embryos of younger age (910,5 days) the second active site is air cell site. The weakest gas exchange was registered in a small
end. “Breathing activity” of egg’s small end increases depending on embryo’s age due to closing of
its allantois. . At day 15th gas exchange here is even more active, than in the air cell site (Figure 1).We
did not found any stable correlations between local gas exchange on separate eggshell sites and total
gas exchange activity. Assuming that as the reason of such correlation’s lack could be a disturbance
of normal gas exchange inside small chambers, we have calculated some parameters of gas exchange
intensity on an eggshell surface unit without chamber and beneath chamber. The differences between
those parameters were not significant, i.e. applied method did not destroy a natural way of gas
exchange. It means, that a reliable evaluation of total breathing activity of an embryo by examination
of gas exchange through a separate part of eggshell surface is practically impossible. Gas content in
an air cell also does not reflect the total level of gas exchange. This confirms with conclusions of Ar
and Meir (1994).
There was established, that during all period between 13-19 days of incubation the CO2/O2 ratio
in air cell site was significantly higher, than in small end. This is due to the fact, that oxygen most
actively penetrates through small and equatorial parts of an eggshell, where allantois is located closer
to eggshell internal surface. More active excretion of CO2 through air cell site can be explained by
CO2 accumulation in air cell during incubation. There also was remarked, that if due to some reasons
gas exchange in equatorial site becomes complicated, the zone of active gas exchange can shift to the
neighbour site for compensation of breathing activity. Similar results were observed on 21 turkey
embryos. This allows to assume, that the biological pattern, revealed on Plymouth Rock embryos is
also applicable to other chicken breeds and strains and other poultry species.
On the base on gained results we can make some practical conclusions. By common way of eggs
setting in commercial incubators, the most gas exchange active sites of an eggshell (equatorial site and
small end) are located unfavourably for gas exchange. The opposite part of an eggshell is positioned
in better conditions, but this site starts to play an important role for gas exchange only after 19th day of
incubation, when internal pecking takes place. At this age the eggs usually are transferred to hatching
trays and are positioned in other way.
Evidently there is an actual task to develop a new design of incubators, taking into
consideration physiological demands of the embryos of modern poultry strains and crosses with high
level of productivity and, respectively, metabolic activity- oxygen consumption. New incubators
will provide more optimal conditions of embryos gas exchange and, thus, better background for
realization of genetic potential of adaptive and performance traits starting from the early stages of
embryogenesis.
References
AR, A., MEIR, M. (1993) Egg air cell gas pressures- what do they represent? Proceedings of the 31st
Annual convention of Israeli Branch of the WPSA, p.72.
BOERJAN, M. (2004) Maximising chick uniformity, performance and vitality. World Poultry, 20:1820
DECUYPERE, E., DEWIL, E., BUYS, N. et al. (1995) Genotype-environment interaction in ascites
sensitivity in broilers. Proceedings of the 11th International Symposium. , Krakow pp 249-252.
DEEMING D.C., BIOL C., BIOL M.I. (1998) Hatchery design into the 21st century: an embryologist’s
perspective. World Poultry, 14: 25-27