It’s a native pork breed exclusive to the Iberian Peninsula unlike white or common pigs which are raised all over the world. This is why there is such a low number of these animals.  The Peninsular Dehesa oak woodlands is the ideal ecosystem for their grazing as part of a unique breeding and feeding system. 
Extremadura has a cold, dry climate which provides the best atmosphere for excellent natural curing of what is considered to be the best ham in the world. It has been covered by the Designation of Origin Dehesa de Extremadura since 1990.
Thus, Iberian pigs have been a part of its landscape since remote times and making ham is a practice that dates back to the Roman era in Extremaduran regions. 
A proclamation by Emperor Diocletian proves that Hispania was already exporting ham to Rome in the Roman Imperial period 2000 years ago. 
Back then, salting was already being used as a method to preserve meat from the primitive Iberian breed. This know-how has been passed done through many generations making it possible for these animals to graze in addition to conserving and improving the Iberian breed.
Nowadays, the historic villa of Trujillo, which was the starting point for Spanish conquerors leaving for the Americas, is the place that combines this tradition and modernity.