I buy my beef from the Muslim guy. After seeing this....

www.theblaze.com/[...]

More on garbage fed cows here:

www.chinahush.com/[...]

I'm not a biologist and surely, eating healthily fed cows is the better option. But also consider the fact that both the cows and we have a digestive system that is very good at getting rid of toxic stuff (liver and kidneys). Therefore, the meat may not be so bad for you at all. Perhaps even healthier than the hormone-grown cows in the West. Secondly, any animal has a general idea of what is edible and what is not. So it won't go for a patch of quicksilver if it can have some rotten cabbage instead.

Personally I think that eating healthy means switching kinds and sources of food often, and in such way reducing the exposure to a single sort of poison which may build up in your body.

Not a Yunnan problem in my opinion.
I see hundreds of cattle grazing feilds all around yunnan.