Saddlebottom by Dick King-Smith

Saddlebottom tells the story of a Wessex Saddleback pig who is born with unusual markings. Instead of the usual white mark over the back and shoulders, typical of the breed, this pig only has one white spot located on his rump. Because of this he gets the nickname Saddlebottom and is ostracised by the other animals on the farm. Saddlebottom is befriended only by a kindly rat who tells him that humans eat pigs. This fear, combined with being an outcast in his own home, leads Saddlebottom to run away from home; adventures and the chance of finding a new home await him.