Which breed of dog is this?

The Great Pyrenees, known as the Pyrenean Mountain Dog outside of North America, is a large breed of dog used as a livestock guardian dog. It should not be confused with the Pyrenean Mastiff.

As late as 1874 the breed was not completely standardized in appearance, with two major subtypes recorded, the Western and the Eastern.

According to the Great Pyrenees Club of America, the Great Pyrenees can be naturally aggressive with any predators that may harm its flock. However, the breed can typically be trusted with small, young and helpless animals of any kind due to its natural guardian instinct.

Males grow to 110–130 pounds (50–59 kg) and 27–32 inches (69–81 cm), while females reach 90–115 pounds (41–52 kg) and 26–31 inches (66–79 cm). On average, their lifespan is 10 to 11 years.

In nature, the Great Pyrenees is confident, gentle and affectionate. While territorial and protective of its flock or family when necessary, its general demeanor is of composure and patience and loyalty.

It is a strong-willed, independent and reserved breed. It is also attentive, quite fearless and loyal to its duties. The Great Pyrenees' size makes it an imposing guardian. A dog of this breed will patrol its perimeter and may wander away if left off its leash in an unenclosed space.

The Great Pyrenees protects its flock by barking and, being nocturnal, tends to bark at night unless trained against such behavior.