According to the Humane Society of the United States, 3–4 million dogs and cats are euthanized each year in the United States and many more are confined to cages in shelters because there are many more animals than there are homes. Spaying or castrating dogs helps keep overpopulation down.[75] Local humane societies, SPCAs, and other animal protection organizations urge people to neuter their pets and to adopt animals from shelters instead of purchasing them.

Although dogs are the most abundant and widely distributed terrestrial carnivores, the potential of feral and free-ranging dogs to compete with other large carnivores is limited by their strong association with humans.[7] For example, a review of the studies in the competitive effects of dogs on sympatric carnivores did not mention any research on competition between dogs and wolves.[108][109] Although wolves are known to kill dogs, they tend to live in pairs or in small packs in areas where they are highly persecuted, giving them a disadvantage facing large dog groups.[108][110]
Humans would also have derived enormous benefit from the dogs associated with their camps.[136] For instance, dogs would have improved sanitation by cleaning up food scraps.[136] Dogs may have provided warmth, as referred to in the Australian Aboriginal expression "three dog night" (an exceptionally cold night), and they would have alerted the camp to the presence of predators or strangers, using their acute hearing to provide an early warning.[136]
Don't overdo bathing. Once every 6 to 8 weeks is typically enough. Professional grooming services are recommended once every 4 to 6 weeks for long haired breeds. Bathing too often can dry out the skin by removing the natural oils. Waterless shampoo can be used between baths to clean feet and other areas. Spot spray directly and sponge off with a damp sponge. Use a hypoallergenic or mild oatmeal shampoo designed for dogs for general bathing. If your pet has a particular skin condition, try hypoallergenic scent free shampoo before the vet. If the condition persists, a medicated shampoo from your veterinarian may be in order. Consult your veterinarian if there are concerns about your pet’s skin.
Dogs bear their litters roughly 58 to 68 days after fertilization,[17][71] with an average of 63 days, although the length of gestation can vary. An average litter consists of about six puppies,[72] though this number may vary widely based on the breed of dog. In general, toy dogs produce from one to four puppies in each litter, while much larger breeds may average as many as twelve.
Their long association with humans has led dogs to be uniquely attuned to human behavior[18] and they are able to thrive on a starch-rich diet that would be inadequate for other canid species.[19] Dogs vary widely in shape, size and colors.[20] They perform many roles for humans, such as hunting, herding, pulling loads, protection, assisting police and military, companionship and, more recently, aiding disabled people and therapeutic roles. This influence on human society has given them the sobriquet of "man's best friend".

The scientific evidence is mixed as to whether companionship of a dog can enhance human physical health and psychological wellbeing.[191] Studies suggesting that there are benefits to physical health and psychological wellbeing[192] have been criticised for being poorly controlled,[193] and finding that "the health of elderly people is related to their health habits and social supports but not to their ownership of, or attachment to, a companion animal." Earlier studies have shown that people who keep pet dogs or cats exhibit better mental and physical health than those who do not, making fewer visits to the doctor and being less likely to be on medication than non-guardians.[194]
A common breeding practice for pet dogs is mating between close relatives (e.g. between half- and full siblings).[81] Inbreeding depression is considered to be due largely to the expression of homozygous deleterious recessive mutations.[82] Outcrossing between unrelated individuals, including dogs of different breeds, results in the beneficial masking of deleterious recessive mutations in progeny.[83]

Yes, though it is usually better to use dog clippers if you can get them. Dog clippers are designed to cut dog's hair, which usually has a coarser top coat and a softer undercoat, but not every dog has this type of coat. For instance, Yorkies and similar breeds only have one type of hair, more like humans, and so it actually makes perfect sense to use human clippers on this kind of dog.

In a study of seven breeds of dogs (Bernese mountain dog, basset hound, Cairn terrier, Epagneul Breton, German Shepherd dog, Leonberger, and West Highland white terrier) it was found that inbreeding decreases litter size and survival.[84] Another analysis of data on 42,855 dachshund litters found that as the inbreeding coefficient increased, litter size decreased and the percentage of stillborn puppies increased, thus indicating inbreeding depression.[85] In a study of boxer litters, 22% of puppies died before reaching 7 weeks of age.[86] Stillbirth was the most frequent cause of death, followed by infection. Mortality due to infection increased significantly with increases in inbreeding.[86]
Neutering reduces problems caused by hypersexuality, especially in male dogs.[76] Spayed female dogs are less likely to develop some forms of cancer, affecting mammary glands, ovaries, and other reproductive organs.[77] However, neutering increases the risk of urinary incontinence in female dogs,[78] and prostate cancer in males,[79] as well as osteosarcoma, hemangiosarcoma, cruciate ligament rupture, obesity, and diabetes mellitus in either sex.[80]

The origin of the domestic dog includes the dog's evolutionary divergence from the wolf, its domestication, and its development into dog types and dog breeds. The dog is a member of the genus Canis, which forms part of the wolf-like canids, and was the first species and the only large carnivore to have been domesticated.[14][26] The dog and the extant gray wolf are sister taxa, as modern wolves are not closely related to the population of wolves that was first domesticated.[14]

Neutering refers to the sterilization of animals, usually by removal of the male's testicles or the female's ovaries and uterus, in order to eliminate the ability to procreate and reduce sex drive. Because of the overpopulation of dogs in some countries, many animal control agencies, such as the American Society for the Prevention of Cruelty to Animals (ASPCA), advise that dogs not intended for further breeding should be neutered, so that they do not have undesired puppies that may later be euthanized.[74]

According to statistics published by the American Pet Products Manufacturers Association in the National Pet Owner Survey in 2009–2010, it is estimated there are 77.5 million people with pet dogs in the United States.[152] The same survey shows nearly 40% of American households own at least one dog, of which 67% own just one dog, 25% two dogs and nearly 9% more than two dogs. There does not seem to be any gender preference among dogs as pets, as the statistical data reveal an equal number of female and male dog pets. Yet, although several programs are ongoing to promote pet adoption, less than a fifth of the owned dogs come from a shelter.
Dogs have been described as carnivores[117][118] or omnivores.[17][119][120][121] Compared to wolves, dogs have genes involved in starch digestion that contribute to an increased ability to thrive on a starch-rich diet.[19] Based on metabolism and nutrition, many consider the dog to be an omnivore. However, the dog is not simply an omnivore. More like the cat and less like other omnivores, the dog can only produce bile acid with taurine, and it cannot produce vitamin D, which it obtains from animal flesh. Also more like the cat, the dog requires arginine to maintain its nitrogen balance. These nutritional requirements place the dog part-way between carnivores and omnivores.[122]
Various kinds of service dogs and assistance dogs, including guide dogs, hearing dogs, mobility assistance dogs, and psychiatric service dogs provide assistance to individuals with disabilities.[160][161] Some dogs owned by epileptics have been shown to alert their handler when the handler shows signs of an impending seizure, sometimes well in advance of onset, allowing the guardian to seek safety, medication, or medical care.[162]

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