I have a collection of bones from my recent cowpool, and the one I just roasted appear to be spine. Is it okay to make broth from spine bones? Specifically, I fear mad cow =(
If I was going to bet on it, I'd say there is BSE in the US. Certainly not a high incidence, but non-zero. In all likelihood, the animal you procured was a relatively young animal (less likely to have BSE). It was, likely, a healthy animal (farmers who are willing to produce a quality product are more likely to have stringent health practices/statuses.) Know your source.
All in all, the risk is non-zero, but pretty low. It's probably more likely that your meat is contaminated with some pathogen that will kill you before it's infected with BSE that will result in a vCJD infection.
I just had some were sold as neck bones. Not very good broth, but I figure it's my nose-to-tail obligation to consume them. I didn't think about mad cow, but no sign of symptoms yet. I'll get back to ya after this giant rabbit stops screaming at me and these leprechauns stop messing with my shoelaces.