The first I learned about bovine serum was when researching vaccines for our child. It's in several of them, along with products from many other animals. I already knew we didn't want to inject it in our bodies, but had no idea that it was sourced in such a nasty way. i can't bare to look at the pics on the Viva! gallery, the description is graphic enough.
Just wanted to mention that point, as I find even most vegans don't think about vaccines as a source of animal products.
http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/appendices/B/excipient-table-2.pdf