Experimental manipulation of egg quality in chickens: influence of albumen and yolk on the size and body composition of near-term embryos in a precocial bird.

The importance of avian egg components in the determination of hatchling size and quality has yet to be fully evaluated. In the first experiment, 20% of the albumen and/or the yolk was removed from chicken eggs to determine the impact of each egg component on metabolism and various size measures in near-term embryos. Results show that metabolic rate, dry body mass, and internal organ mass are largely independent of egg composition. Removal of albumen resulted in a decrease in wet body mass corresponding to decreases in water content in the body and the yolk sac, and decreased tibiotarsus length. Removal of yolk resulted in no change in body mass, but decreases in both wet and dry yolk sac mass. In a second experiment, removal of 15% of either egg component led to reductions in hatchling mass similar to those observed in whole near-term embryos. Albumen, as the primary source of water in the egg, is the primary determinant of hatchling size and may influence hatchling success through size-related limiting factors. Differences in yolk content may influence neonatal quality as a nutritional supplement, but seem not to result in greater tissue formation during embryonic development.

Regional differences in diffusive conductance/perfusion ratio in the shell of the hen's egg.

Are both gas exchange and gas tensions uniform in different regions of the developing hen's egg? To answer this question we measured the O2 uptake and CO2 production of the whole egg, and at the same time the O2 and CO2 tensions of the air cell. The gas exchange ratio (R) of the whole egg differed from R calculated from air cell PO2 and PCO2 values, in agreement with the findings of Visschedijk [Br. Poultry Sci. 9:173-184 (1968)], who measured gas exchange separately over both the air cell region and the remainder of the egg. We constructed a diffusive shell conductance/perfusion (G/Q) line on the O2-CO2 diagram from a blood nomogram for the chick embryo in late development [Olszowka et al., Fed. Proc. 46:512 (1987)], and used this to analyze our results. The G/Q ratio for the area of shell over the air cell differs from that for the remainder of the egg. Our analysis permits us to calculate, for each area, the regional shell conductance, blood flow, and O2 and CO2 tensions in the gas spaces between the shell and the chorioallantoic capillaries.

Avian eggs: barriers to the exchange of heat and mass.

Measured boundary-layer conductance to heat exchange for bird eggs varies with egg mass to the 0.53 power. Calculations based on the Nusselt-Reynolds relationship for a sphere and the thermal properties of air indicate that the conductance of the boundary layer to heat and to mass at any wind speed other than still air should scale with mass to the 0.53 power. Although the boundary layer contributes little to the total barrier to mass flux between bird eggs and their environment, we show that it is the major barrier to the exchange of heat. From these observations we infer that birds incubating eggs in natural nests can alter only the gradient affecting mass flux between their eggs and the environment while having the capability to change both the gradient and conductance affecting heat flux.

The reliability of respiratory quotient measurements.

A graphical analysis is presented which allows the assessment of confidence in the measurement of the respiratory quotient in an open-circuit metabolic chamber as a function of an organism's metabolic rate, the chamber ventilation, the magnitude of the respiratory quotient and the sensitivity of the gas analyzers.