The Chihuahua Listeni/tʃɪˈwɑːwɑː/ (Spanish: chihuahueño) is the smallest breed of dog and is named for the state of Chihuahua in Mexico. Chihuahuas come in a wide variety of sizes, head shapes, colors, and coat lengths.
The Chihuahua’s history is puzzling and there are many theories surrounding the origin of the breed. Both folklore and archaeological finds show that the breed originated in Mexico. The most common and most likely theory is that Chihuahuas are descended from the Techichi, a companion dog favored by the Toltec civilization in Mexico. No records of the Techichi are available prior to the 9th century, although dog pots from Colima, Mexico, buried as part of the western Mexico shaft tomb tradition which date back to 300 BC are thought to depict Techichis. It is probable that earlier ancestors were present prior to the Mayans as dogs approximating the Chihuahua are found in materials from the Great Pyramid of Cholula, predating 1530 and in the ruins of Chichen Itza on the Yucatán Peninsula.
In fact, wheeled dog toys representing both the "deer head" and "apple head" varieties of Chihuahua have been unearthed across Mesoamerica from Mexico to El Salvador. The earliest of these were found at Tres Zapotes in Veracruz, Mexico, which date to 100 AD. Dog effigy pots dating to around 1325 AD discovered in Georgia and Tennessee also appear to represent the Chihuahua It has been argued that these pots arrived with survivors from the Casas Grandes site in Chihuahua, Mexico, after it was attacked and destroyed around 1340 AD. Pots unearthed at Casas Grandes include representations of the "deer head" variety of Chihuahua. Hernan Cortés wrote, in a 1520 letter, that the Aztecs raised and sold the little dogs as food. Colonial records refer to small, nearly hairless dogs at the beginning of the 19th century, one of which claims 16th-century Conquistadores found them plentiful in the region later known as Chihuahua.
A progenitor of the breed was reputedly found in 1850 in old ruins near Casas Grandes in the Mexican state of Chihuahua from which the breed gets its name, although most artifacts relating to its existence are found around Mexico City. A pot featuring the "deer head" variety of Chihuahua has been unearthed at Casas Grandes which dates from 1100–1300 AD showing the long history of the breed at this site. A wheeled dog toy which has been dated to 100 AD from Tres Zapotes in Veracruz, Mexico, depicts a dog identical in appearance and size to the modern Chihuahua, indirect evidence that the breed was in Mexico over 1400 years before the first Europeans arrived. The Chihuahua has remained consistently popular as a breed, particularly in America when the breed was first recognized by the American Kennel Club in 1904.
This breed requires expert veterinary attention in areas such as birthing and dental care. Chihuahuas are also prone to some genetic anomalies, often neurological ones, such as epilepsy and seizure disorders.
Chihuahuas, and other toy breeds, are prone to the sometimes painful disease hydrocephalus. It is often diagnosed by the puppy having an abnormally large head during the first several months of life, but other symptoms are more noticeable since "a large head" is such a broad description. Chihuahua puppies exhibiting hydrocephalus usually have patchy skull plates rather than a solid bone and are typically lethargic and do not grow at the same pace as their siblings. A true case of hydrocephalus can be diagnosed by a veterinarian, though the prognosis is grim.
Overfeeding a Chihuahua can be a great danger to the dog's health, shortening its life and leading to diabetes. Many Chihuahuas have molleras, or a soft spot in their skulls, and they are the only breed of dog to be born with an incomplete skull. This is not a defect; it is a normal adaptation facilitating the passage through the birth canal and growth and development of the domed type of forehead. The molera is predominant in the rounder heads often and is present in nearly all Chihuahua puppies. The molera fills in with age, but great care needs to be taken during the first six months until the skull is fully formed. Some moleras do not close completely and if particularly large will require extra care to prevent injury. Many veterinarians are not familiar with Chihuahuas as a breed and mistakenly confuse a molera with hydrocephalus.
Chihuahuas can also be at risk for hypoglycemia, or low blood sugar, which is especially dangerous for puppies. Left unattended, hypoglycemia can lead to coma and death but can be avoided with frequent feedings, especially for chihuahuas who are younger, smaller or leaner. Chihuahua guardians should have a simple sugar supplement on hand to use in emergencies, such as Nutri-Cal, Karo syrup and honey. These supplements can be rubbed on the gums and roof of the mouth to rapidly raise the blood sugar level. Signs of hypoglycemia include lethargy, sleepiness, low energy, uncoordinated walking, unfocused eyes and spasms of the neck muscles or head pulling back or to the side, fainting and seizures.
As in other breeds with large protruding eyes, Chihuahuas are prone to eye infections or eye injury. The eyes may water frequently in response to dry air, dust or air-borne allergens. Daily wiping will keep the eyes clean and minimize tear staining.
Collapsed trachea is a health concern that is characteristic of the chihuahua breed.
Chihuahuas have a tendency to tremble or shiver when stressed, excited or cold. Chihuahuas, especially the short-coat variety, are less tolerant of cold than larger breeds, and may require a sweater or boots in cold weather. They will seek warmth in sunshine, under blankets, or on furniture, human laps or the back of a larger dog.
Although figures often vary, as with any breed, the average lifespan range for a healthy Chihuahua is between 12 and 20 years.
Chihuahuas are sometimes picky eaters and care must be taken to provide them with adequate nutrition. Sometimes wet or fresh food can have the most appealing smell to these constant eaters. Chihuahuas are prone to hypoglycemia and could be at a critical state if allowed to go too long without a meal. At the same time, care must be exercised not to overfeed them.
Chihuahuas have a notorious problem with dental issues. Dental care is a must for these little creatures. Over-feeding and insufficient exercise can result in an overweight Chihuahua. Overweight Chihuahuas are susceptible to increased rates of joint injuries, tracheal collapse, chronic bronchitis, and shortened life span.
Chihuahuas are also known for a genetic condition called 'luxating patella', a genetic condition that can occur in all dogs. In some dogs, the ridges forming the patellar groove are not shaped correctly and a shallow groove is created. In a dog with shallow grooves, the patella will luxate or slip out of place, sideways. It causes the leg to 'lock up' and will force the chihuahua to hold its foot off the ground. When the patella luxates from the groove of the femur, it usually cannot return to its normal position until the quadriceps muscle relaxes and increases in length, explaining why the affected dog may be forced to hold his leg up for a few minutes or so after the initial displacement. While the muscles are contracted and the patella is luxated from its correct position, the joint is held in the flexed or bent position. The knee cap sliding across the femur can cause some pain due to the bony ridges of the femur. Once out of position, the animal feels no discomfort and continues with activity.
Chihuahuas are also prone to some heart-related disorders, such as heart murmurs and pulmonic stenosis, a condition in which the blood outflow from the heart's right ventricle is obstructed at the pulmonic valve.
Chihuahuas, along with other miniature dogs such as Chinese Cresteds, are prone to physical deformities, especially in old age; several chihuahuas and cross-bred chihuahua/Chinese crested mixes have rated highly in the World's Ugliest Dog Contest, including a purebred chihuahua named Princess Abby (winner of the 2010 contest) and a crossbreed named Yoda (the 2011 winner).