Through offal-based feed, through feces, and through blood- or endocrine-based IV medications. In humans, it is also passed through blood transfusions.
This is the part which I was inquiring. If God only wants us to eat animals which chew cud, and He does not want us to boil a calf in its mother's milk, then it is most logical to assume that He does not want us to feed ground up cow flesh to cows (making them cani-bulls :)). Again, had we followed God's rules, we wouldn't be in this mess to begin with, no?