Anyone see Google results for "milch cow"? 15,300 results. Surprising to me, as I hadn't seen the term before.
There's a war boat with the name, and a book with that title, and also lots of references to the animal using that term.
I'm not familiar enough with it to know if there's any commercial value in the term or domain, so I'll abstain from valuating it. Interesting domain at least.
It is a cow but producing more milk than usual...
Its is similiar to the term "cashcow" which dates only from about 1970, "milch cow" was used in exactly the same way from 1601 (answers.com)