The National Thanksgiving Turkey Presentation probably started as an informal tradition by Harry Truman. Every year, the President of the United States is presented with one or more turkeys that would otherwise be slaughtered and they pardon them, aka they won't be eaten during thanksgiving.
However, what you may not know is that these turkeys are raised to be pardoned. Their caretakers know that they're not for eating as soon as they're born. They're trained to handle loud noises, flash photos and large crowds. However, they're still raised as if they would be slaughtered for eating.
That causes a problem for them. These turkeys are fattened so much that they become obese and experience health problems due to their large size. Heart disease, respiratory failure and joint damage are some of the problems they have. Due to them, most of the pardoned turkeys actually have a very short life after the ceremony and they die within a year of being pardoned.