Wikisimpsons - The Simpsons Wiki
After applying to buy his own Krusty Burger franchise, Homer must watch a training video. According to the video, the grassy pampas of Patagonia are where the "Krustyburgers of the future graze". Krusty then appears and says that he comes down "South America way" to buy only the best beef, although he notes that best is not a recognized USDA grade.
He then goes on to say that a cows a cow, and that it's all the same once the ketchup goes on. However, the cow he points at is drooling and looks somewhat sick. Krusty then steps in something and exclaims "Oh, my Go--." At that point Homer interrupts the video, claiming it to be boring.
 Behind the Laughter
The cow that Krusty points to would appear to have Mad Cow Disease.