Cull cows

I hauled 3 'cull' cows to the sale barn today. What an expensive lesson. One cow was a "Freemartin", which means that she is sterile.  Apparently when a cow has twins of each sex, then the bull twin will be fertile, but the female twin will be sterile. WHO KNEW? How does one go about acquiring such knowledge, other than by making mistakes? I bought this cow as a breeding heifer & have now put two and 1/2 years of feed, vaccines, etc. (expenses) into her only to find out that she is a freemartin & thus sterile.  Therefore, I had to sell her as a slaughter cow as opposed to a breeding cow - slaughter price being much lower. What a bummer!