Mad Cow Disease

In a rural program for farmers, there was a female reporter seeking the main cause of mad cow disease, she arranged an interview with a farmer who may have some theories on the matter. This was what went down:

LADY REPORTER: I am here to gather as much information I can get on the possible sources of mad cow disease.

The Farmer stared at the reporter and said "Do you know that a bull mounts a cow once in a year?"

REPORTER [embarrassed]: Well sir, that's new information, but what relationship exists between this and the mad cow saga?
FARMER: And do you know that we milk a cow twice a day?
REPORTER: This is a valuable information sir, but what about getting to the point?
FARMER: I am getting to the point, just imagine that I was playing with your tits twice a day, and screwing you once a year, wouldn't you get mad?