The Yorkshire Terrier is one of the smallest dog breed of terrier type, and of any dog breed. The breed developed during the 19th century in Yorkshire, England. Ideally its maximum size is 7 pounds (3.2 kg). A popular companion dog, the Yorkshire Terrier has also been part of the development of other breeds, such as the Silky Terrier. Yorkshire Terriers do tend to bark a lot. Factors such as stress, fatigue, a cold environment, poor nutrition, and a change in diet or feeding schedule may bring on hypoglycaemia. Low blood sugar can also be the result of a bacterial infection, parasite or portosystemic liver shunt.