反馈抑制器；

Feedback Suppressor;

乳汁里有一种称为“哺乳反馈抑制素”（FIL）的乳清蛋白，如果有一段时间乳汁未被排出，它就会开始产生并聚集。

There is a certain whey protein in the milk, called Feedback Inhibitor of Lactation (FIL), that begins to build up and concentrate when milk is not removed for a while.