(Brief background for the non-American readers: tomorrow is a national holiday called Thanksgiving. A turkey feast is the traditional offering.)
Slate has a wonderful article on how they manage to have so many turkeys ready at one time (The Turkey-Industrial Complex). The most popular turkey is the White Broad Breasted Turkey which has been bred for large size. So large, in fact, they are unable to reproduce; the species is kept around by artificial insemination (WARNING: some of you may not enjoy this video very much)
As a bonus, here’s MSNBC mocking Palin during some turkey pardoning event. She’s doing an interview while turkeys are being terminated in full view in the background.
Enjoy your turkey, people.