In the last few days, food safety bloggers Bill Marler and Amy Derby have suggested that meat from the 143 million pound Hallmark/Westland "downer cow" recall should be tested. In my opinion, the only ones who would benefit from that idea would be the testing labs.
Marler suggests that the meat could be tested for mad cow, Salmonella and E. coli. Screening for mad cow prions is most effective when carried out on brain or nerve tissue, where the prions are most heavily concentrated. It would be far easier to find a needle in a haystack than to find a random few mad cow prions in 143 million pounds of meat. And a "negative" result for Salmonella or E. coli O157:H7 would be equally meaningless.
As Marler pointed out, there is an ethical dilemma here. Is it appropriate to discard meat that is likely safe to eat because some unknown fraction of it came from "downer" cows? I don't know the answer to that question. But I am certain of one thing. The answer won't come from testing.