I'm not sure if Bob covered this in the TSE/prions lecture, but some meat industries use "downer" cows, or cows that have unknown disabilities that prevent them from moving as effectively as other cows. There are obvious and terrifying implications of this- a faulty gate is one of the first signs of "Mad Cow" or BSE infection, which we know can cause "human" BSE, or vCJD. This is a really scary loophole that the industry has been using for decades.
Well, the USDA just changed that! As an effort to boost public confidence in US meats, the USDA has closed this loophole and banned the use of these "downer" cows in meat processing. Since the discovery of "Mad Cow," the USDA banned the use of downers, but allowed for the use of cattle that became disabled after their preslaughter inspection. Again, as we all know, the "incubation period" of BSE and all the prion diseases is 5-10 years, so even a cow that is just showing signs of this has likely been infected for a long time- a useless and very harmful loophole. Regardless, the use of downers came to the spotlight in January when the Humane Society released undercover tapes of a slaughterhouse in Chino, CA using all sorts of mechanisms to move disabled cows. This resulted in a public outcry and the largest US meat recall in history: over 143 million pounds of beef.
Full story at http://www.cidrap.umn.edu/cidrap/content/other/bse/news/may2108downers.html.