>What is a "downer" in this context?

An animal that has been injured while in transit. Sometimes they break a leg or some other problem (which could be a disease like BSE-mad cow). These were immediately sent to slaughter. No more with the new laws since last week.

I believe that over 140,000 cows per year are considered downers in the US alone. I understand, and agree that they should not enter the food-chain without being checked as before. But this poses a huge problem now. What to do with 140,000 carcases, most of which do not have any disease, simply bad luck?