"母牛流产了“ － "The cow cast her calf"? HSK Anki flash cards
流产 means "to have a miscarriage, to have an abortion". The former in case it happened as a natural process, the latter in case it was enforced.

So you can translate 母牛流产了 means "the cow had a miscarriage". 

To cast means "To give birth prematurely" in this context, so the translation is incorrect.

This definitely is not something you need to know for HSK 1 (even for the old exam).