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Zinc is an important mineral that is required for normal bone development. However, the direct effects of zinc on the mineralization of bone cells of human origin are not clear. The objective of this study was to determine the effects of zinc on the differentiation of SaOS-2 human osteoblastlike cells and the formation of mineralized bone nodules. Cells were cultured for 8 d and then transferred to zinc-free medium and treated with varying concentrations (0-50 microM) of zinc. Alkaline phosphatase (ALP) activity was used as a measure of osteoblast differentiation, and bone nodules were detected by von Kossa staining. After 4, 6, and 8 d of treatment, zinc increased ALP activity at 1 and 10 microM, but decreased activity at 50 microM. After 9 d of treatment, zinc increased both the number and area of mineralized bone nodules at low concentrations (1 and 10 microM), but decreased both at higher concentrations (25 and 50 microM). These findings demonstrate that zinc has biphasic effects on the differentiation and mineralization of human osteoblast-like cells.

A 16-week experiment was conducted to compare effects of various levels of sodium selenite (SS) and Se-enriched yeast (SY), on the whole-egg Se content and hen's productivity. One hundred Shaver 579 hens, 27 weeks old, were placed on one of five experimental treatments. Each treatment was replicated four times with five hens per cage. Treatments consisted of feeding a low Se diet without supplementation (basal diet) or basal diet with one of two levels of supplemented Se (0.4 or 0.8 mg/kg) supplied by SS or SY. All supplemented treatments had significantly higher whole-egg Se concentration from basal diet (P < 0.05). On the same supplemented level, hens fed on SY had higher egg Se content from hens feed on SS (P < 0.001). No effects of dietary treatments on egg weight, percentages of dirty and cracked egg, and feed intake and conversion of feed were observed throughout the trial (P < 0.05). In the first 8 weeks, there was no significant difference (P < 0.05) in hen-day egg production among treatments. From the ninth week on to the end of the trial, supplementation of SY to hen's diet resulted in a higher egg production than SS (P < 0.01).

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