Studies on the reduction of heavy metal pollution from animal waste - The availability of trace mineral and its distribution in the digestive tract -

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Zinc pollution from animal waste becomes serious problem, which results from the low availability of zinc in the conventional feeds. In the first experiment, we studied the zinc distribution in the digesta of pigs given a conventional diet (soybean meal-based) or skim milk-based diet that showed high availability of zinc. Zinc solubility in the small-intestinal digesta was lower in the soybean meal group than in the skim milk group. There was much high-molecular-weight complex with zinc in the liquid phase of digesta of skim milk group but not in that of soybean meal group.These results suggest that phytate in a conventional diet reduces zinc availability through suppressing zinc solubility in the digest and that hydrolyzed products of skim milk in the digestive tract make complexes with zinc, which increase zinc availability. In the second experiment, we developed new zinc sources as feed additives and evaluated their availabilities. An in vitro digestion study indicated that these new products did not show higher solubility in the artificial digesta than zinc sulfate did. However, dietary zinc amino acid chelate showed higher availability in pigs than zinc sulfate. The advantage of the organic zinc is considered to result from its high solubility in the digesta. In the third experiment, we studied the removal of phytate that adversely affected zinc availability. The fermentation with Aspergillus degraded phytate in soybean meal. This treatment improved zinc availability in rats and pigs. The addition of Aspergillus phytase to swine diet improved zinc availability. Although the supplemental yeast phytase also degraded phytate in pigs, the efficacy was less in the yeast phytase than in the Aspergillus phytase.