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

由于传统饲料中锌的利用率低，动物粪便中的锌污染问题日益严重。在第一个试验中，我们研究了锌在猪消化系统中的分布，这些猪分别饲喂锌含量较高的传统日粮（豆粕为主）和脱脂乳为主的日粮。豆粕组锌在小肠食糜中的溶解度低于脱脂乳组。脱脂乳组消化液中存在较多的高分子量锌配合物，豆粕组消化液中没有。这些结果表明，常规日粮中的植酸盐通过抑制锌在消化道中的溶解度来降低锌的利用度，而消化道中脱脂牛奶的水解产物与锌形成复合物，从而增加锌的利用度。在第二个试验中，我们开发了新的锌源作为饲料添加剂，并评价了它们的可利用性。体外消化研究表明，这些新产品在人工食糜中的溶解度并不比硫酸锌高。然而，饲粮中氨基酸螯合锌的利用率高于硫酸锌。有机锌的优点被认为是由于它在食糜中的高溶解度。在第三个实验中，我们研究了对锌可用性不利的植酸盐的去除。曲霉发酵可降解豆粕中的植酸盐。这种处理提高了大鼠和猪的锌利用率。饲粮中添加植酸曲霉酶可提高锌的利用率。虽然添加酵母植酸酶也能降解猪体内的植酸，但酵母植酸酶的效果不如曲霉植酸酶。

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.