Cocker Spaniel

Cocker Spaniels are dogs belonging to two breeds of the spaniel dog type: the American Cocker Spaniel and the English Cocker Spaniel, both of which are commonly called simply Cocker Spaniel in their countries of origin. In the early 20th century, Cocker Spaniels also included small hunting Spaniels.

Cocker Spaniels were originally bred as hunting dogs in the United Kingdom, with the term cocker deriving from their use to hunt the Eurasian woodcock. When the breed was brought to the United States, it was bred to a different standard, which enabled it to specialize in hunting the American woodcock. Further physical changes were bred into the cocker in the United States during the early part of the 20th century.

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Spaniels were first mentioned in the 14th century by Gaston III of Foix-Béarn in his work the Livre de Chasse. The "cocking" or "cocker spaniel" was a type of field or land spaniel in the 19th century. Prior to 1901, Cocker Spaniels were only separated from Field Spaniels and Springer Spaniels by weight. Two dogs are considered to be the foundation sires of both modern breeds, the English variety are descended from Ch. Obo, while the American breed descends from Obo's son, Ch. Obo II. In the United States, the English Cocker was recognized as separate from the native breed in 1946; in the UK, the American type was recognized as a separate breed in 1970. In addition, there is a second strain of English Cocker Spaniel, a working strain which is not bred to a standard but to working ability. Both breeds share similar coat colors and health issues with a few exceptions.

Sources:
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Information from wikipedia - https://en.wikipedia.org/wiki/Cocker_Spaniel