The Gran Mastín de Borinquen, also known as the Puerto Rican Mastiff, Mastín Borincano, Becerillo de Borinquen and Perro Barsino de Hacienda, is the only breed native to the island of Puerto Rico.
This rare breed was developed by blending together island dogs, various molosser lines, and Spanish Mastiffs up until the early 1900s.
The breed has historical relevance during the time of the Spanish conquest of the Americas. Due to the rarity of the breed and its lack of existence beyond Puerto Rico, the breed lacks a formal standard but informally, based on appearance, resembles that of smaller mastiff types, often with brindle coloration.
Currently, the greatest threat to the breed's continued existence is the current embargo placed on Cuba and the impoverished state of much of Purto Rico's population.