The immunization effect is one of the key links which affect on pig feeding.
猪场免疫效果好坏是关系到养猪成败的关键环节之一。
The three key links are technical links, management links and theoretical link.
三个关键环节是：技术环节、管理环节和理论环节。
This next section of code adds all of the foreign key links seen in the previous diagram.
下面的代码将添加上图中的所有外键链接。
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