Egg Water Vapour Conductance Research Articles

Cuticle deposition improves the biosecurity of eggs through the laying cycle and can be measured on hatching eggs without compromising embryonic development

The cuticle is part of the egg's natural defense and it can be improved by genetic selection. Prior to adoption of this measurement in breeding programs, questions that need to be addressed are whether improved cuticle deposition will result in a reduced risk of eggs becoming contaminated and whether selection for this trait will have any unintended consequences on the incubation process. Bacterial penetration experiments were carried out using eggs from a pedigree line of broiler breeders (BB) and Rhode Island Red (RIR) layers. Within the natural variation in cuticle deposition in each line, a good cuticle was shown to reduce an egg's susceptibility to penetration by Escherichia coli (BB, P = 0.023) and Salmonella typhimurium (RIR, P < 0.001). Deglycosylation of cuticle proteins had little effect on their antimicrobial activity. The effect of bird age on cuticle deposition was also examined. Shell color decreased with age as anticipated; however, we found no evidence that cuticle deposition decreases with age, at least up to 50 wk. A thicker cuticle could affect the water vapor conductance (WPC) of hatching eggs. The WPC of eggs was, therefore, measured on eggs selected from the top and tail of the cuticle distribution, this time in a Lohmann Selected Leghorn (LSL) pedigree line. Broiler breeder eggs were also tested. No evidence of a relationship between cuticle deposition and WPC was found for LSL or BB eggs. Cuticle deposition measurements require eggs to be stained. Here, we show that this has no adverse effect on embryo development at d 12 of incubation. Thus, we conclude that cuticle deposition is important in preventing bacterial penetration of eggs in genetically divergent breeds of chicken and that the measurement can be practically incorporated into breeding programs. This will contribute to improving the biosecurity of eggs by reducing vertical and horizontal transmission of potentially zoonotic and pathogenic organisms from parent to offspring.

Development of the chick embryo: effects of egg mass

We asked to what extent, within a species, differences in egg mass, hence in eggshell surface area and O 2 conductance, could affect the development of the avian embryo. Large (L, about 70 g) and small (S, about 55 g) fertile chicken eggs were simultaneously incubated and the embryos studied at day 18, i.e. before the onset of lung ventilation. Embryo mass and O 2 consumption (V̇ O 2 ) (measured with a manometric technique) normalized per mass of the freshly laid egg were higher in S than in L, while no differences occurred after normalization by egg surface area (S.A.). Egg water vapour conductance, which is proportional to O 2 conductance, was also found to be directly proportional to egg S.A. Hence, the mass and V̇ O 2 of the embryo are more closely related to the O 2 conductance of the eggshell than to egg mass, giving support to the concept that the avian embryo's V̇ O 2 is not an invariable species characteristic, but a variable dependent on O 2 availability. Hatching and viability did not differ between L and S, and the specific mass of heart and lung and their cellular (DNA) concentration were also similar between the two groups of embryos. Therefore, differentiation of tissues and organogenesis do not seem to be affected by the differences in total O 2 availability determined by the differences in egg mass, while they are probably more important than total tissue mass in setting the time of hatching.

Nest Microclimate, Water-Vapor Conductance, and Water Loss in Heron and Tern Eggs

Abstract Rates of water loss (ṀH2O) were measured in eggs of seven species of tree-nesting Ciconiiformes and three species of ground-nesting Charadriiformes during natural incubation. Measurements of egg temperature, conductance of the egg shell to water vapor, and nest and ambient humidity allow one to calculate the difference in water-vapor pressure (ΔP) between egg and nest and between nest and ambient air. ΔP between egg and nest was significantly lower in ground-nesting species (23 torr) than in tree-nesting species (31 torr). We suggest that low ΔP in ground-nesting species was due to relatively high humidity (ca. 27 torr) in nests built on the ground compared to the humidity in loose stick nests of tree-nesting species (ca. 14 torr). Water-vapor conductance of eggs from more humid nests is relatively higher than that of eggs from less humid nests (107% and 78% of predicted values, respectively), resulting in similar fractional losses in mass for the whole incubation period in both groups of birds. (ṀH2O) was not always constant throughout incubation. We suggest that changes in (ṀH2O) may be due to changes in ambient humidity and/or egg temperature.

Water-Vapor Conductance of Black-Billed Magpie (Pica pica) Eggs Collected along an Altitudinal Gradient

Water-vapor conductance was determined for 78 eggs of Black-billed Magpies (Pica pica) collected along an altitudinal gradient in north-central Colorado and south-eastern Wyoming (range 1,486-2,896 m). Conductance of magpie eggs to water vapor is a function of the number of eggs in nests at the time of collection, indicating that conductance may be related to the order in which an egg is laid. A statistical relationship between altitude and conductance of eggs in our samples probably is spurious, and we conclude that water-vapor conductance of eggs does not vary altitudinally within the geographic area encompassed by our study. The altitudinal decline in water-vapor conductance that has been reported for eggs of several other species of birds seems not to characterize eggs of magpies.