Moose was born on Christmas Eve, 1990 in Florida, the youngest littermate. He was the largest puppy in the litter. Like Pal, the original Lassie, the obstreperous puppy was too much for his original owner. According to an article by Lori Golden:
In fact, chasing cats was one of the activities that led to this troubled terrier becoming one of TV’s most precious pooches. Originally owned by a Florida family, Sam and Connie Thise, Moose was too hard to handle. He couldn’t be house trained; he chewed everything; he dug and barked a lot; and he was constantly escaping and climbing trees. Eventually given to the Florida manager of Birds and Animals Unlimited, a company that trains animals for TV and motion pictures, Moose was put on a plane at 2½ years old and sent to Mathilde DeCagny, an LA trainer working for the show-biz animal company.