working dog, classification used by breeders and kennel clubs to designate dogs raised by humans to herd cattle and sheep, as draft animals, as message dispatchers in wartime, in police and rescue work, as guardians of persons and property, or as guides (see guide dog) for the blind. The following breeds are designated working dogs by the American Kennel Club: Alaskan malamute, Belgian Malinois, Belgian sheepdog, Belgian Tervuren, Bernese mountain dog, Bouvier des Flandres, boxer, Briard, bull mastiff, Cardigan Welsh corgi, collie, Doberman pinscher, German shepherd, Great Dane, Great Pyrenees, komondor, kuvasz, mastiff, Newfoundland, old English sheepdog, Pembroke Welsh corgi, puli, Rottweiler, Samoyed, schnauzer (giant and standard), Shetland sheepdog, Siberian husky, and St. Bernard. See dog.

toy dog, classification used by breeders and kennel clubs to designate very small breeds of dogs kept as pets. Some are selectively bred diminutive forms of larger breeds and others are naturally small. The following breeds are designated as toy dogs by the American Kennel Club: affenpinscher, Brussels griffon, Chihuahua, English toy spaniel, Italian greyhound, Japanese spaniel, Maltese, miniature pinscher, papillon, Pekingese, Pomeranian, pug, Shih Tzu, silky terrier, toy poodle, toy Manchester terrier, and Yorkshire terrier. See dog.

sporting dog, classification used by breeders and kennel clubs to designate dogs bred for pointing, flushing, and retrieving game. These dogs hunt by air scent—as opposed to most hounds, which are ground scenters—and their quarry is primarily game birds. Included are the pointers, setters, retrievers, and spaniels. Pointers stand with nose and body rigidly still in front of their quarry, thus directing the hunter to its location. The setters were originally trained to set, or crouch, in front of game, the hunter then making the capture with a net. As bird shooting became popular, setters were trained to point. Retrievers find and return killed game to the hunter. Land spaniels spring, or flush, game, i.e., they startle a bird from its cover into flight. Water spaniels and many retrievers are especially equipped, as with a water-repellent coat and webbed feet, for retrieving downed waterfowl. The following breeds are designated sporting dogs by the American Kennel Club: American water spaniel, Brittany spaniel, Chesapeake Bay retriever, clumber spaniel, cocker spaniel, curly-coated retriever, English cocker spaniel, English setter, English springer spaniel, field spaniel, flat-coated retriever, German shorthaired pointer, German wirehaired pointer, golden retriever, Gordon setter, Irish setter, Irish water spaniel, Labrador retriever, pointer, Sussex spaniel, Vizsla, Weimaraner, Welsh springer spaniel, and wirehaired pointing griffon. See dog.

seeing-eye dog: see guide dog.

prairie dog, short-tailed, ground-living rodent, genus Cynomys, of the squirrel family, closely related to the ground squirrels, chipmunks, and marmots. There are several species, found in the W United States and N Mexico. Prairie dogs, named for their barking cries, are 12 to 15 in. (30 to 36 cm) long, including the 1- to 4-in. (2.5 to 10 cm) tail, and have short, coarse, buff-colored fur. The black-tailed prairie dog, Cynomys ludovicianus, is found on the Great Plains. Members of this species live in connecting burrows, forming colonies, or "towns," which may extend many miles and include thousands of individuals. The entrances of the burrows are surrounded by cone-shaped mounds, which serve to keep out rainwater; the entrance shafts drop straight down for several feet. Prairie dogs spend much time maintaining the mounds by tamping down damp earth. They often sit upright on their haunches in rows, one animal on each mound; this behavior has given them the name "picket pins" in some regions. At any sign of danger the animals give a warning cry and duck down into the burrows. Rattlesnakes and burrowing owls sometimes live in the burrows and prey on young prairie dogs. Three species of white-tailed prairie dogs inhabit open or brushy valleys of the Rocky Mts; their burrows are usually less extensive than those of the black-tailed species. Prairie dogs feed mainly on grasses, but also eat insects; they hibernate in winter. Prairie dog towns were formerly much more common and extensive than now; some towns on the plains encompassed millions of individuals. Ranchers regard the animals as competitors for grazing lands and have destroyed them in large numbers. Prairie dogs are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Rodentia, family Sciuridae.

police dog: see German shepherd.

nonsporting dog, classification used by breeders and kennel clubs to designate dogs that may formerly have been bred to hunt or work but that are now raised chiefly as house pets and companions. The following breeds are classified as nonsporting dogs by the American Kennel Club: Boston terrier, bulldog, chow chow, Dalmatian, French bulldog, Keeshond, Lhasa apso, poodle, and schipperke.

guide dog, a dog trained to lead a blind person. The first school for training such dogs was established by the German government after World War I for the benefit of blinded veterans. Schools now exist in several European countries and the United States, where the pioneer Seeing Eye, Inc., founded by Dorothy Harrison Eustis in 1929 and established near Morristown, N.J., in 1932, is the best known. The master spends about a month at the school training with the already trained dog and is usually charged a nominal fee. Although the German shepherd is by far the most widely used breed for guide-dog work, several other breeds, e.g., the golden retriever, the Labrador retriever, and the Doberman pinscher, have been trained successfully for this work. Approximately 10% of the blind population can use seeing-eye dogs successfully, that fraction including scores of persons who have achieved new independence through their assistance. Applicants may be rejected on the basis of sufficient useful vision, advanced age, poor health, or unsuitable temperament.

dog racing, trials of speed between dogs. Now contested on oval tracks, the sport developed from the ancient practice of coursing, in which specially trained dogs chase game animals in the open field. Whippets chased live rabbits until the protests of humane groups had the practice outlawed. Artificial hares, first tried in 1876 in England, eventually became standard and greyhounds, accustomed to hunting by sight and sound rather than by smell, replaced whippets. The sport became popular in the United States in the 1930s when some states permitted wagering. Dog tracks are popular in Florida, Massachusetts, and some western states as well as in England, Ireland, Australia, Spain, and Indonesia.

dog days, name for the most sultry period of summer, from about July 3 to Aug. 11. Named in early times by observers in countries bordering the Mediterranean, the period was reckoned as extending from 20 days before to 20 days after the conjunction of Sirius (the dog star) and the sun. In the latitude of the Mediterranean region this period coincided with hot days that were plagued with disease and discomfort. The time of conjunction varies with difference in latitude, and because of the precession of the equinoxes it changes gradually over long periods in all latitudes.

dog, carnivorous, domesticated wolf (Canis lupus familiaris) of the family Canidae, to which the jackal and fox also belong. The family Canidae is sometimes referred to as the dog family, and its characteristics, e.g., long muzzle, large canine teeth, and long tail, as canine traits. However, the unmodified term dog usually refers only to the domestic subspecies Canis lupus familiaris.

Two characteristics distinguish the dog from other canids and, indeed, from all other animal species. The first is its worldwide distribution in close association with humans, encompassing both hemispheres from the tropics to the Arctic. The second is the enormous amount of variability found within the subspecies. For example, the Irish wolfhound may stand as high as 39 in. (99.1 cm) at the shoulder, while the Chihuahua's shoulder is usually no more than 6 in. (15.2 cm) from the ground; the silky coat of the Yorkshire terrier may be 2 ft (61 cm) long, while a few breeds of dog (such as the Mexican hairless) are entirely without hair. The evolution of such widely differing breeds has been heavily influenced by conscious human selection, in addition to natural evolution.

Dogs have been selectively bred through the centuries for special purposes, notably to pursue and retrieve game, as draft animals, as guides (e.g., for the blind), and as companions. Although dogs possess hearing abilities far superior to humans', their acute sense of smell is probably the sense most utilized. In addition to traditional hunting and tracking, the dog's sense of smell has been put to such diverse uses as the location of exotic foods and the detection of drugs and explosives, e.g., in luggage and packages.

Dogs can be protected against serious diseases for which vaccines are available; these include distemper, canine hepatitis, leptospirosis, and rabies.

Early Dogs

The dog is descended from the wolf. True wolves appeared in Europe about one million years ago and in the Americas some 700,000 years later. Dog remains estimated to be about 14,000 years old have been found in Germany, and younger remains have been found in Israel (about 13,500 years old) and Idaho (about 10,500 years old). It is probable that the dog was the first animal to be domesticated, most likely around 15,000 years ago. Domestication may have occurred independently in a number of different areas of the world, but genetic tests show that all dogs are descended from an Eurasian stock, even the now extinct pre-Columbian dogs of the Americas.

It is thought that the earliest domesticated dogs resembled the present-day dingo, the wild dog of Australia. The dingo is believed to have come to Australia as a domestic dog with the aborigines from Southeast Asia. Although more historical information exists on the forerunners of European dogs (such as the British hounds, terriers, and shepherd dogs) than on those of other areas, there is evidence that dogs have existed in most areas of the world throughout the period of recorded history. One of the oldest known breeds is the basenji, which originated in central Africa and is still used as a hunter by certain tribes in that region. Several distinct breeds were known in ancient Egypt and a mastifflike breed (resembling the Kurdish dog in present-day Iraq) is found in Babylonian illustrations of c.2200 B.C.

Dog Breeds

The Purebred Dog

A breed of dog is produced by selecting and mating dogs with certain desired characteristics. The offspring of such matings are then inbred, i.e., mated with litter mates or close relatives. After about eight generations, the line usually breeds true, i.e., most offspring resemble each other. Then standard traits can be established for the new breed. A purebred dog is one that conforms to the standards of a certain breed and whose lineage, or pedigree, has been recorded for a certain period of time.

One of the principal functions of a kennel club is to maintain the records of lineage of individual purebred dogs in order to preserve breed standards. The stud books of the AKC contain entries for all purebred dogs whose owners have elected to register their dog's pedigree. Other stud books, such as those of the United Kennel Club, often record dogs of breeds not recognized by the AKC but which have a considerable following in the United States. Dogs of mixed origin or whose parentage is unknown are called mongrels.

Classification of Breeds

Attempts to classify dogs probably date from the time when humans discovered that certain canine traits were more useful than others. The earliest known system of classification, that of the Romans, included categories for house dogs, shepherd dogs, sporting dogs, war dogs, dogs that ran by scent, and dogs that ran by sight. Today there are systems of classification and breeding in most countries of Western Europe and in North America, many using a variation of the standard British system.

In the United States, the classification system most frequently encountered is that employed by the American Kennel Club (AKC), which recognizes more than 150 of the more than 200 known breeds. The breeds are grouped into six classes. In the sporting dog group are pointers, retrievers, setters, and spaniels. These dogs hunt by air scent as opposed to those of the hound group, e.g., beagles, foxhounds, and bloodhounds, which track their prey by ground scent. Also classified as hounds are those dogs of the greyhound type, e.g., whippets, borzois, and Salukis, which hunt mainly by sight. The many breeds of terrier go to earth after their burrowing prey. Among the working dog group, used as guards, guides, and herders, are the collie, the German shepherd, and the St. Bernard. Such diminutive pet dogs as the Pekingese, the Pomeranian, and the pug belong to the toy dog class. The nonsporting dog group is a class of dogs bred principally as pets and companions and includes the Boston terrier, the bulldog, the chow chow, the Dalmatian, and the poodle. In addition to the breeds in the above classes, the AKC currently places additional breeds in a miscellaneous group; breeds recently recognized by the club are placed in this class until they become established. Included are the Akita of Japan, the Australian cattle dog, the Australian kelpie, the Bichon Frise (a French descendant of the water spaniel), the border collie (an English shepherd dog), the cavalier King Charles spaniel, the Ibizan hound (of Spanish origin), the miniature bull terrier, the soft-coated wheaten terrier (from Ireland), the Spinone Italiano, and the Tibetan terrier.

Dogs registered by the AKC and other registry associations compete regularly in dog shows and field trials. In dog shows, the various breeds are judged solely on appearance, while in field trials they are rated according to their hunting skills.

See articles on individual dog breeds.

Reproduction

Female dogs, or bitches, will mate only when in heat, or estrus, which occurs about every six months and lasts from 18 to 22 days. Whelping (giving birth) occurs after a gestation period of about nine weeks. The size of the litter varies to some extent with the size of the dog: toy dogs rarely bear more than 2 puppies, while the largest breeds average closer to 10.

coach dog: see Dalmatian.

Dog Star: see Sirius.

Bernese mountain dog, breed of sturdy working dog first brought to Switzerland by the invading Roman armies over two millennia ago. It stands from 23 to 27 in. (58-69 cm) high at the shoulder and weighs from 50 to 70 lb (23-32 kg). Its long, silky, slightly wavy coat is jet black with a white blaze up the face, white on the chest, feet, and tip of tail, and russet-brown or tan markings on all four legs and above the eyes. For hundreds of years in its native canton of Bern, the Bernese mountain dog was used as a draft animal by the local merchants to haul cartloads of goods to market. Today it is raised principally for show competition and as a pet. See dog.

Australian cattle dog, breed of medium-sized herding dog developed in Australia. It stands from 18 to 20 in. (45.7-50.8 cm) high at the shoulder and weighs about 33 lb (15 kg). Its double coat consists of a soft, dense underlayer and a moderately short, straight topcoat that forms a fringe of slightly longer hair on the back of the forelegs and thighs. The coat may be blue, blue mottle, or red speckled in color. Believed to be the product of crosses among the Australian kelpie, the dingo, and the smooth collie, the Australian cattle dog ranks among the world's best herding dogs. It is sometimes called the Australian heeler, a name derived from the dog's habit of nipping at the heels of stray cattle to direct them back to the herd. The breed is exhibited in the miscellaneous class at dog shows sanctioned by the American Kennel Club. See dog.

Sport of racing sleds pulled by dogs over snow-covered cross-country courses. It developed from a traditional Eskimo method of transportation. Modern sleds are usually of wood (ash) construction, with leather lashings and steel- or aluminum-covered runners. Sled dogs are usually Eskimo dogs, Siberian huskies, Samoyeds, or Alaskan malamutes; teams typically consist of 4–10 dogs. The course is usually 12–30 mi (19–48 km) long, though some, including the Iditarod, are considerably longer.

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Any working dog used to pull a sled carrying people and supplies across snow and ice. The breeds most commonly used are the Alaskan malamute, Laika, Samoyed, and Siberian husky. All are powerful dogs with a thick coat and high endurance. Seealso Eskimo dog.

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or Seeing Eye dog

Dog professionally trained to guide and protect its blind master. They have also been used to assist persons with hearing impairments and restricted mobility. Systematic training of guide dogs originated in Germany during World War I to aid blinded veterans. At the age of approximately one year, the dog is trained for three or four months. Retrievers and German shepherds are the most widely used breeds.

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Any of five species (genus Cynomys) of short-legged, terrestrial squirrels, named for their barklike call. Once abundant throughout the plains of the western U.S., part of southern Canada, and northern Mexico, they are now found mostly in isolated or protected areas. They are 12–17 in. (30–43 cm) long, including a 1–5-in. (3–12-cm) tail. Their main diet is grass. Colonies consist of well-defined territories defended by a male, several females, and young. The burrows of the black-tailed prairie dog have carefully tended funnel-shaped entry mounds that prevent flooding and serve as lookout posts. The white-tailed prairie dog inhabits higher altitudes, hibernates, and is less colonial.

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Breed of long-haired toy dog developed in ancient China, where it was held sacred and was kept in Peking's Imperial Palace. Looting English forces introduced the breed to the West in 1860. Known as the “lion dog” for its full mane but perhaps also for its courage, it stands 6–9 in. (15–23 cm) and weighs up to 14 lbs (6.5 kg). It has hanging ears, a short, wrinkled muzzle, and a black mask across the face. The coat may be solid or variegated. Chinese royalty carried very small Pekingese, called “sleeve dogs,” in their sleeves.

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or dog salmon

Lightly speckled North Pacific fish (Oncorhynchus keta) of the salmon family. The chum salmon ranges from the Mackenzie and Lena rivers in the southern Arctic southward to Japan and the Rogue River. Its weight averages about 10–12 lbs (4.5–5.5 kg). During the autumn spawning season it swims more than 2,000 mi (3,200 km) up the Yukon River.

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Any member of the canine genus Canis, particularly the domestic species, Canis familiaris. Domestic dogs seem to have decended from the wolf or a wolflike ancestor. Dogs were apparently the first animals to be domesticated, and domestication seems to have begun in various parts of the world at roughly the same time. Selective breeding by humans has resulted in myriad domestic breeds that vary widely in size (from the tiny Chihuahua to the huge mastiff), physical form (e.g., the short-legged dachshund and the flat-faced bulldog), coat texture and length (e.g., the sleek Doberman pinscher and the long-haired Afghan hound), and behavioral patterns (e.g., sporting dogs, toy dogs, and working dogs). The American Kennel Club now recognizes almost 150 breeds; other clubs, such as the United Kennel Club, recognize many more.

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or Dog Star

Brightest star in the night sky (apparent magnitude −1.44), a binary star about 8.6 light-years from the Sun in the constellation Canis Major. The bright component of the binary is a blue-white star 23 times as luminous as the Sun, about twice the size, and considerably hotter; its companion was the first white dwarf star discovered. Its name probably comes from a Greek word meaning “sparkling” or “scorching.” The ancient Egyptians used its predawn rising to predict the annual flooding of the Nile. The ancient Romans associated the rising of the Dog Star at dawn with the hottest part of the year, called the “dog days.”

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Breed of Swiss working dog brought to Switzerland over 2,000 years ago by invading Romans. The hardy breed was widely used to pull carts and to drive cattle to and from their pastures. It has a broad chest, hanging V-shaped ears, and a long, silky, black coat. Markings include brown spots on the chest and forelegs and over the eyes, and sometimes white on the chest, nose, feet, and tail tip. The breed stands 21–28 in. (53–70 cm) high and weighs about 90 lbs (40 kg).

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