To the untrained eye, the American boxer and the German boxer look pretty much alike. Differences between the two are subtle, not drastic, but they do exist. They aren't different breeds, but differing types, with some differences in bone structure, amount of white permitted and snout size. It's not uncommon for well-bred dogs to have mixed bloodlines.
The boxer was developed in Germany during the 19th century. Related to many bulldog type canines, the boxer's closest canine ancestor was the bullenbeisser, a word translated as "bull-biter." His ancestry includes terriers, Great Danes and English bulldogs, along with ancient Tibetan fighting dogs and Spanish boar-hunting canines. German hunters developed the boxer to seize game and hold it until hunters arrived. They bred dogs for strong, wide, powerful mouths. The American Kennel Club's first boxer registration occurred in 1904, although it wasn't until the World War II era that the dog became popular in the United States.
The AKC standard calls for male boxers to stand between 23 to 25 inches tall at the shoulder at maturity, with females slightly smaller at 21.5 to 23.5 inches. The AKC standard permits either cropped or natural ears. If cropped, the ears are tapered and long, rising when something alerts the dog. Tail docking is required if showing in conformation classes. The American boxer's nose is larger and its muzzle is wider than his German cousin. Boxer colors include fawn and brindle, the latter a black striping effect on a lighter background. American boxers can have white markings as long as the white areas don't exceed 33 percent of the coat.
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The German Boxer Klub, through the Verband fur das Deutsche Hundewesens -- the German version of the Kennel Club -- sets the German boxer standard, in partnership with the Fédération Cynologique Internationale. The German boxer sports somewhat larger bones than the American variety. The German breed specifies a height for adult males of between roughly 22.5 and 25 inches. Females stand between approximately 21 inches to 23.5 inches tall. While the AKC boxer standard doesn't specify weight, the German standard states that male dogs should weigh approximately 66 pounds and females about 55 pounds. The German standard also permits natural or cropped ears, but not tail docking. The colors for the German boxer are the same as the American. While white markings aren't "completely rejected," they aren't encouraged, either.
Although there may be slight size differences between the American and German boxer, the temperament is similar. Certain individual bloodlines might produce more aggressive or better hunting tendencies, but that isn't a reflection of either variety of dog overall. The ideal boxer, American or German, is loyal, smart, easily trained, energetic, outgoing, protective and fun-loving. Boxers should never be shy. In the registries of both countries, boxers are considered members of the working group, canines bred for guarding and rescue.