Abstract
Tsaiya ducks and Leghorn hens are the two major laying birds raised in Taiwan. They are all excellent egg layers. Tsaiya ducks are small in body size (1.3 kg) with bigger egg weight (65 g) and stronger eggshell breaking strength than eggs from hens. The eggshell consists mainly of calcium carbonate, hence calcium plays an important role in the eggshell formation. Magnesium is also present in eggshell in small amounts, which may have effect on maintaining eggshell quality. In comparison studies, it was shown that the duck eggshells contained higher calcium and lower magnesium content than chicken eggshells. The eggshell magnesium content was not affected by the dietary magnesium levels (690-2380 ppm) in ducks, but in hens, it increased linearly with dietary magnesium levels. The palisade layer (5000×) of the eggshell was found to have a compact form for ducks while there are many hallow vesicles in chicken eggshells. The eggshell magnesium deposition model is different for ducks and hens with ducks having a one-peak and hens having a two-peak model. The calcium deposition model is similar for both birds. Both the carbonic anhydrase specific activity and total activity in the shell gland mucosa of ducks are higher than those in hens. Ducks retain higher magnesium and lower calcium in the shell gland mucosa and secret less magnesium and more calcium into the shell gland lumen for eggshell deposition. The ATPase specific activity is maintained fairly constant during the eggshell forming stage, indicating continuous calcium transport into the shell gland lumen for eggshell formation. The magnesium content in duck eggshells is much lower than that in hens indicating that the magnesium content in the eggshell may have an effect on eggshell quality. (Asian-Aust. J. Anim. Sci. 2003. Vol. 16, No. 2 : 290-296)
Highlights
Leghorn hens and Tsaiya ducks are the two major egg laying fowls raised in Taiwan
Tsaiya ducks and Leghorn hens (Chen and Shen, 1989), we found that the magnesium content (0.13%) in the eggshell was lower in duck eggs than in chicken eggs (0.41%)
The results showed that as the calcium intake was sufficient for both ducks and hens to maintain normal egg production, the dietary calcium content had no effect on the carbonic anhydrase activity in the shell gland mucosa
Summary
Leghorn hens and Tsaiya ducks are the two major egg laying fowls raised in Taiwan. They play an important role in Taiwan’s poultry industry. Statistics Yearbook (2000), the numbers of Leghorn hen and Tsaiya duck raised in Taiwan are 35,375,000 and 2,921,000, respectively, with an annual egg production of 7,270 million eggs for hens and 478 million eggs for ducks. The laying ducks raised in Taiwan are called Tsaiya ducks or domestic ducks Tsaiya ducks are good egg producers with a small body size (1.2-1.4 kg) and lay eggs (16 wk) earlier than white. Duck eggs are normally larger with a thicker eggshell and higher egg breaking strength than chicken eggs
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