Xoloitzcuintle

A 1999 genetic study using mitochondrial DNA found that the DNA sequences of the Xoloitzcuintle were identical to those of dogs from the Old World.[8] In 2018, an analysis of DNA from the entire genome indicated that domesticated dogs entered North America from Siberia for 4,500 years and were isolated for the next 9,000 years. After contact with Europeans, these dogs were replaced by Eurasian dogs and their local descendants. The pre-contact dogs exhibited a unique genetic signature that is now almost gone[9] due to their assimilation into the Eurasian dog gene pool. In 2020, the sequencing of ancient dog genome indicates that in two Mexican breeds the Chihuahua and Xoloitzcuintli derive 4% and 3% of their ancestry from pre-colonial dogs,[10] almost entirely being descended from Eurasian dogs.

Their phenotype is a consequence of canine ectodermal dysplasia caused by a mutation on the Foxl3 autosomal gene.[11]

The breed did not receive any official notice in its homeland until the 1950s. The FCI, founded in 1940, was not prepared to declare the Xolo an official purebred at that time. According to breed historian Norman Pelham Wright, author of The Enigma of the Xoloitzcuintli, Xolos began to turn up at Mexican dog shows in the late 1940s. Although they were recognized as indigenous specimens of a native breed, interest in them was minimal at that time, because information was scarce and no standard existed by which to judge them. Within a decade, the FCI realized that the breed would become extinct if drastic action were not taken to save it. This led to the widely publicized Xolo Expedition of 1954. With the official sanction of the FCI, Wright and a team of Mexican and British dog authorities set off to discover if any purebred Xolos still existed in remote areas of Mexico. Eventually 10 structurally strong Xolos were found and these dogs formed the foundation of Mexico's program to revive the breed. A committee headed by Wright authored the first official standard for the breed; on May 1, 1956, the Xolo was finally recognized in its native land and, as Mexico is a member of the FCI, worldwide.

Xolos were among the first breeds recorded by the American Kennel Club (AKC). A Mexican dog named "Mee Too" made breed history as the first AKC-registered Xolo in 1887. "Chinito Junior", bred and owned by Valetska Radtke of New York City, became the breed's only AKC champion to date. He earned his title on October 19, 1940.[12]

In 1959, the Xolo was dropped from the AKC stud book due to the breed's scarcity and perceived extinction. The Xoloitzcuintli Club of America (XCA), the official parent club for the breed, was founded on October 26, 1986, to regain AKC recognition for the breed. On May 13, 2008, AKC voted to readmit the breed to its Miscellaneous Class starting January 1, 2009. The founding members voted unanimously to recognize all three sizes (toy, miniature and standard) and both varieties (hairless and coated) at their initial meeting. Since then, the XCA has compiled a stud book modeled on requirements for eventual AKC acceptance, held an annual independent specialty show, published a quarterly newsletter, The Xolo News, and maintained an active national rescue network, National Xolo Rescue (known before 2009 as The Xolo Rescue League[13]). Since January 1, 2007, FSS registered Xolos have been eligible to compete in AKC performance events. The breed was moved into the AKC Studbook in December 2010 and has been eligible to be shown in the AKC Non-Sporting group since January 1, 2011.[14]

The breed ranges in size from about 10 to 55 lb (5 to 23 kg). The height is 9 to 26 inches (23–67 cm). 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.[15] 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.[16] 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.[17] 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.[18] 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 the skin is often marked, splashed, or spotted. The most common colors are various shades termed black, grey, bronze, yellowish-blonde, blue and red. The breed occurs in a range of sizes, which breeders have standardized into three designations: Standard, Miniature and Toy.

The Xoloitzcuintle has a calm and attentive temperament.[19]

The Xolo has been developed by natural selection for thousands of years, and is therefore generally not prone to health and structure problems as other dog breeds more modified by human selection efforts. Xolos came from tropical climates and are not suited for outdoor life in colder temperate and northern climates; they should be considered an indoor dog breed. They need bathing, light grooming and skin care as with other dogs of similar physical type, or acne can result. Most skin problems arise from poor breeding, neglect, or over-bathing and over-lotioning, stripping natural protections and clogging pores.[20][21]