There are over 800 dog breeds currently recognized by various
kennel clubs worldwide. As all dog breeds have been derived from mixed-breed dog populations, the term "purebred"
has meaning only with respect to a certain number of generations. Moreover, many dogs, especially outside the
United States and Western Europe, belong to no recognized breed.
A few basic breed types have evolved gradually during the
domesticated dog's relationship with man over the last 10,000 or more years, but most modern breeds are of
relatively recent derivation. Many of these are the product of a deliberate process of artificial selection.
Because of this, some breeds are highly specialized, and there is extraordinary morphological diversity across
different breeds. Despite these differences, dogs are able to distinguish dogs from other kinds of
The definition of a dog breed is a matter of some controversy. Some
groups use a definition that ultimately requires extreme in-breeding to qualify. Dogs that are bred in this manner
often end up with severe health problems. Other reorganizations define a breed more loosely, such that an
individual may be considered of one breed as long as, say, three of its grandparents were of that breed. These
considerations come into play among breeders who enter their dogs in dog shows.
Purebred dogs frequently suffer from serious inherited health
and/or behavioral problems. This is by no means true of the majority of purebred dogs, and the same problems can
occur in populations of mixed breed dogs. Even prize-winning purebred dogs are sometimes possessed of crippling
genetic defects due to inbreeding.
The behavior and appearance of a dog of a particular breed can be
predicted fairly accurately, while mixed-breed dogs show a broader range of innovative appearance and
Mixed-breed dogs are dogs that do not belong to specific breeds, being mixtures of two
or more. Mixed breeds, or dogs with no purebred ancestry, are not inherently "better" or "worse" than
purebred dogs as companions, pets, working dogs, or competitors in dog sports. Sometimes mixed-breed dogs are
deliberately bred, for example, the Cockapoo, a mixture of Cocker Spaniel and Miniature
Such deliberate crosses may display hybrid vigor and other
desirable traits, but can also lack one or more of the desired traits of their parents, such as temperament or a
particular color or coat. However, without genetic testing of the parents, the crosses can sometimes end up
inheriting genetic defects that occur in both parental breeds. Deliberately crossing two or more breeds is also a
manner of establishing new breeds.
Unlike undomesticated canine species, where the females typically
come into estrus (also called in season or in heat) once a year, usually in late winter, and bear one litter of young, the female of the domestic
dog can come into season at any time of the year and usually twice a year. Most bitches come into season for the
first time between 6 and 12 months, although some larger breeds delay until as late as 2 years. Like most mammals,
the age that a bitch first comes into season is mostly a function of her current body weight as a proportion of her
body weight when fully mature rather than age, with the different maturation rates of the various sizes of dogs
accounting for this variation in age of first season. The amount of time between cycles varies greatly among
different dogs, but a given dog's cycle tends to be consistent through her life.
Dogs bear their litters roughly 9 weeks after
Catahoula Leopard Dog nursing litter of puppies
An average litter consists of about six
puppies, especially for breeds that
have not strayed too far from their wild ancestors. However, litters of many more or only one or two puppies
are also common. Some breeds have a tendency to produce very large litters. Since a mother can provide milk
for only a few of those puppies, humans must assist in the care and feeding when the litter exceeds eight or
Some breeds have been developed to emphasize certain physical
traits beyond the point at which they can safely bear litters on their own. For example, the Bulldog often requires
artificial insemination and almost always requires cesarean section for giving birth.
Puppies often have characteristics that do not last beyond early
puppyhood. For example, eyes are often blue when they first open but change to other colors as the puppy matures.
As another example, Kerry Blue Terrier puppies have black coats when they are born and their distinctive "blue"
color appears gradually as the puppy nears maturity. The ears of erect-eared breeds such as the German Shepherd Dog
are softly folded at birth but straighten as the puppy grows.
Dog experts advise that dogs not intended for further breeding
should be spayed or neutered so that they do not have undesired puppies, which are often abandoned or are
euthanized due to lack of space and resources in shelters. Abandoned dogs often go feral and form predatory packs
that attack livestock and occasionally also prove dangerous to humans. Spaying and neutering can also help prevent
diseases such as breast cancer and prostate cancer that occur as the unneutered animal ages (due to hormonal
changes). Also, it is not required for a female dog to either experience a heat cycle or have puppies before
spaying; likewise, a male dog does not need the experience of mating before neutering. These myths account for
numerous health problems and unwanted puppies.
here to view our Dog Breed
For more info on aspects of dog breeding and all
dog breeds, please see our Topical