| Summary: | 博士 === 臺灣大學 === 動物科學技術學研究所 === 98 === The pigmentation of avian eggshell is a complex process controling by two types of pigments, biliverdin and protoporphyrines. Biliverdin, a green pigment, is a byproduct of hemoglobin breakdown and will eventually display a blue and/or green color on the eggshell. In contrast to biliverdin, protoporphyrines is an immediate precursor of the heme molecule, and will give eggshells a reddish and/or brown color. The native Brown Tsaiya duck (Anas platyrhynchos) is a major laying duck breed in Taiwan and their eggshell color can vary from white to dark blue. It is possible that the shell gland of blue-shelled ducks (BSD) can accumulate higher concentration of biliverdin than white-shelled ducks (WSD) do. However there is no strong evidence to prove this assumption.
In the present study, attempts were made to identify whether the higher bioactivity of heme oxygenase found in the BSD shell gland was responsible for the higher concentration of biliverdin observed. The processes of pigment deposition of eggshell in ducks were also investigated.
Ultraviolet spectrophotometery and HPLC were applied to determine the concentrations of biliverdin within tissues of shell glands, uterine fluid as well as eggshells from both of BSD and WSD, at 6, 12, 18, 20 and 23.5 h post oviposition, respectively. Significant differences in biliverdin concentrations were found in the eggshell and uterine fluid of BSD and WSD, but not in the shell gland. Comparatively, the activity of heme oxygenase in the shell gland remained constant throughout the ovulatory cycle in both breed. HO1 immunoreactivity was observed in all the shell glands studied and present in the cytoplasma of stratified cuboid epithelial cells in the crypts of shell glands. The mRNA levels of aminolevulenic acid synthase one, heme oxygenase one, and heme oxygenase two in the shell gland were not significantly different between WSD and BSD. The exogenous injection of biliverdin into the shell gland antrum in the WSD resulted in increase of biliverdin deposition in the eggshell. Using the layer-by-layer dissolution assay, it was found that biliverdin concentration in the first to sixth layers of the eggshell in the BSD was significantly higher than that in the white-shelled counterpart. However, the BSD eggshells did not accumulate a large quantity of biliverdin in the most external layer, the deposition tended to increase layer by layer.
Taken together, the data indicated that the color differences between egg shell of BSD and WSD were influenced by the amount of biliverdin in the uterine fluid rather than by the amount of biliverdin in the shell gland. The results imply that a mechanism controlling the biliverdin transportation from the shell gland into the uterine fluid may play a key role in regulating the duck eggshell colors.
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