African wild dog

The Xoloitzcuintli, or Xolo for short, is a hairless breed of dog, found in toy, miniature, and standard sizes. The Xolo also comes in a coated variety and all three sizes can be born to a single litter. It is also known as Mexican hairless dog in English-speaking countries, and is one of several breeds of hairless dog.

In Nahuatl, from which its English name originates, its name is xoloitzcuintli (singular) and xoloitzcuintin (plural). The name xoloitzcuintli comes from the god Xolotl and itzcuintli , meaning dog in Nahuatl.

A genetic study was recently conducted in order to determine the origin of the Xoloitzcuintli breed. The study did not find a close genetic relationship between Xoloitzcuintli and the Chinese Crested Dog, another hairless breed that is cited by the American Kennel Club as an ancestor to the Xoloitzcuintli. However, the study showed that this breed did not result from a separate domestication of dogs in the New World. Xoloitzcuintli appear to have been a result of a mixture of several Old World dog breeds. The breed ranges in size from about 10 to 50 lb (4 to 20 kg). Similar in appearance to a Pharaoh Hound, with a sleek body, almond-shaped eyes, large bat-like ears, and a long neck, the Xolo is notable for its dominant trait of hairlessness. The dominant hairless trait originated in this breed as a spontaneous mutation thousands of years ago. The recessive expression of the trait will produce a coated variety, which is genetically inseparable from the hairless, as the homozygous appearance of the hairless mutation is fatal to the unborn pup. Most litters contain both hairless and coated puppies. The coated variety, covered with a short, flat dense coat represents the original form of the dog, prior to the occurrence of the spontaneous hairless mutation. The hairless variety is completely hairless on the body, with many dogs exhibiting a few short hairs on the top of the head, the toes, and the tip of the tail. Most hairless dogs are black or bluish-gray in color. The allele responsible for the Xolo's hairlessness also affects the dog's dentition: Hairless Xolos typically have an incomplete set of teeth while the dogs of the coated variety have complete dentition.

The Xolo is moderate in all aspects of its appearance, conveying an impression of strength, agility, and elegance. Xolo body proportions are rectangular, slightly longer in total body length than the height measured at the highest point of the withers (top of the shoulders). The breed occurs naturally in two varieties, hairless and coated. Hairless Xolos are the dominant expression of the heterozygous Hh hairless trait. Coated Xolos (hh) are the recessive expression, and breeding hairless to coated or hairless to hairless may produce pups of either or both varieties. Breeding coated to coated will only produce coated pups because they are recessive to the hairless trait and do not carry the dominant H gene.
Both varieties occur in all hair or skin colors, and often marked, splashed, or spotted. The most common colors are various shades termed black, blue, and red. The breed occurs in a range of sizes, which breeders have standardized into three designations. The Xoloitzcuintli's 'primitive' temperament (very high intelligence, sensitivity, high energy, inquisitiveness, strong hunting, and social instincts) is apparent because the breed's temperament was not modified overall by selective breeding in their native history in Mexico. This has also ensured a sturdy physical nature and vigorous health generally innate in both coated and uncoated Xolos. Adult Xolos are frequently noted for their calm demeanor, although puppies can be extremely energetic, noisy, and very oral until they reach maturity (after 2 years old), after which they tend to settle down and become more calm. Inadequately supervised or exercised Xolos can become escape artists, climbing and jumping fences to chase. Many individuals of this breed can possess guard dog ability and will not back down from a fight. At the same time, adult dogs, when they are raised properly, can become steady, well-behaved, and affectionate companions.

Though physically grown at one year, many dog breeds including Xolos, are not 'emotionally mature' until around two years. Like active breeds such as terriers, Xolos need calm, consistent, and loving obedience training and regular socialization during their growing years. Well-raised Xolos bond strongly with their owners, becoming highly devoted to their families while frequently choosing one specific family member as favorite.

Anyone considering acquiring a Xolo should expect to spend time educating themselves in positive dog training techniques, and, ideally, should have prior experience with active and intelligent dog breeds. A spacious, well-fenced, and safe physical environment is desirable for this breed. Daily walks are ideal for exercising most toy-sized Xolos, however more stimulating physical and mental exercise is advised for larger and more active individuals. Behavior problems in Xolos are typically a result of a dog receiving inadequate or inconsistent supervision, as well as inadequate exercise and mental stimulation. The Xoloitzcuintli is a social dog that should not, in most cases, be an "only dog". It does not do well when kept as an outside-only dog. This is a breed that is at its best when it is made part of the family, receiving regular interaction and socialization with its humans (and other dogs, whether present in the home or as regular playmates). In domestic dogs, sexual maturity begins to happen around age six to twelve months for both males and females, although this can be delayed until up to two years old for some large breeds. This is the time at which female dogs will have their first estrous cycle. They will experience subsequent estrous cycles semiannually, during which the body prepares for pregnancy. At the peak of the cycle, females will come into estrus, being mentally and physically receptive to copulation. Because the ova survive and are capable of being fertilized for a week after ovulation, it is possible for a female to mate with more than one male. 2-5 days after conception fertilization occurs, 14-16 days later the embryo attaches to the uterus and after 22-23 days the heart beat is detectable.

Dogs bear their litters roughly 58 to 68 days after fertilization, with an average of 63 days, although the length of gestation can vary. An average litter consists of about six puppies, 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.

Some dog breeds have acquired traits through selective breeding that interfere with reproduction. Male French Bulldogs, for instance, are incapable of mounting the female. For many dogs of this breed, the female must be artificially inseminated in order to reproduce. Despite their descent from wolves and classification as Carnivora, dogs are variously described in scholarly and other writings as carnivores or omnivores. Unlike obligate carnivores, dogs can adapt to a wide-ranging diet, and are not dependent on meat-specific protein nor a very high level of protein in order to fulfill their basic dietary requirements. Dogs will healthily digest a variety of foods, including vegetables and grains, and can consume a large proportion of these in their diet, however all-meat diets are not recommended for dogs due to their lack of calcium and iron. Comparing dogs and wolves, dogs have adaptations in genes involved in starch digestion that contribute to an increased ability to thrive on a starch-rich diet.