An internet search has proven me correct, but has also confirmed what others have said. There was indeed only one cow, originally named Minnie Moo. Some websites have altered the name, probably due to gender confusion - an obviously female bovine wearing a male icon - I can understand the confusion. Mickey Moo, Minnie Moo - I suppose the cow didn't really care, but as far as Colson39's claim to more than one - I challenge you to a duel!
By the way, after M Moo's demise, there was some most excellent roast served at TE.
And I shall win that duel!!! I'm sorry FtWildernessGuy, but there actually WERE two different cows, one named Minnie Moo and one named Mickey Moo. They were around at different times for the most part. And just in case there is any question, I present you with the below (you can clearly notice the difference in the markings):
Here is Mickey Moo:


And Minnie Moo:



Mickey Moo was in Disneyland, Minnie Moo was in Disney World. That might be why you think there is only one

Do not challenge the master!!!

I think I deserve a free Kungaloosh for this...