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Full-grown miniature pigs
A miniature pig (also mini pig, or micro pig, or teacup pig, or "designer pig", or "nano pig", or "apartment pig", or "pocket pig") is a breed of pig developed and used for medical research or as a pet. Miniature pigs weigh between 50–150+ pounds when fully grown. Mini pig has become an acceptable term that is used to distinguish the difference between farm pigs and smaller breeds such as potbellied pigs.
In the 1960s, Chinese pigs that grew to be 150–200 pounds (68–91 kg) were sent to zoos in Western nations and were used for medical research in the fields of toxicology, pharmacology, pulmonology, cardiology, aging, and as a source of organs for organ transplantation. These comparatively smaller pigs were easier to work with than the larger farm pigs, which typically reach weights of 300-500 pounds. Pot-bellied pigs also became a fixture in many zoological parks where their small stature, sway backs, and potbellies attracted the attention of visitors. The purchase of a few potbellied pigs by wealthy pet owners helped start a new trend in pet pigs.
The popularity of miniature pigs grew in the 1980s, with pet potbellied pigs appearing everywhere from New York apartment complexes to small hobby farms. However, the trend was short-lived, mostly due to city ordinances forbidding raising farm animals within the city limits. Furthermore, many owners came to realize that even a 165-pound pig was difficult to handle in most housing situations.
The 1990s and 2000s saw a rising trend of marketing pet pigs that were supposed to be much smaller than even the potbellied pigs, and therefore suitable pets for house and apartment owners. While multiple animal protection groups and pig breeders question or deny the existence of true "miniature pigs", there are currently breeders selling piglets claimed to be miniature pigs in North America and in the United Kingdom. The misleading terms have grown to include other adjectives to represent breeds that do not exist.
In the mid-1980s, Keith Connell of the Bowmanville Zoo in Ontario imported breeding potbellied pigs to Canada, which became the foundation for the potbellied pig in North America. Because of customs laws, only their offspring could be sold in the United States. US zoos were the main target for the piglets, but private owners soon began purchasing them as pets. Up to five additional imports were made in the following 10 years. To track the pedigrees, the Potbellied Pig Registry Service, Inc (PPRSI) was created to preserve these bloodlines and establish a breed registry in the United States. This registry was dissolved in the late 1990s.
The Miniature Potbellied Pig Registry Service, Inc (MPPRSI) was established in 1993 to provide a registry for those pigs who were pedigreed in the PPRSI and met the breed standard, when fully grown not being more than 15 inches (38 cm) tall and weighing under 55 pounds (25 kg). All of the foundation pigs were dual registered in PPRSI and MPPRSI.
In May 2015, the China Academy of Agricultural Science announced that its research team had successfully produced F-25 (the 25th generation) of inbred Chinese Wuzhishan Mini Pig (WZSP), with an inbreeding coefficient of 0.99519.
Miniature pigs, also known as micro pigs, pocket pigs, and or teacup pigs, can be used as pets. They are very intelligent animals (4th smartest among mammals) and can be easily house-trained. They can also be taught how to go through a doggy door or ring a bell at a door to notify their owners if they need to go outside. They are hypoallergenic and often do well with people that have usual animal allergies as they have hair and not fur. They do, however, "blow their coat" meaning that they shed most of the longer hair once a year, usually in Spring or early summer to prepare for the warmer months ahead. Because pigs do not sweat (the often used term "I'm sweating like a pig" is a misnomer since pigs only sweat a small amount from their snouts), they shed to help keep cool in the warmer summer months. This can often be a hassle as they can shed a large amount of long, stiff hair that can pierce through the skin if stepped on or embedded in clothing. It is common for the pig to gain bald spots or be mostly bald through summer and fall, and most of the hair will grow back. Though the main assumption about pigs is that they are very dirty animals, in fact, they will usually only get muddy or dirty when provided with a much needed outside area to gain vitamin D from sun/rooting soil and grass for a diet, and use the mud as a sunscreen or cooling agent to keep their body temperature regulated. Wallowing, as it is referred to, is when a pig will root up a certain area of dirt and roll around in the mud to get a nice layer of mud on their skin to protect against the sun and as a bug repellent.
Breeders claim that micro pigs can potentially make great pets, but that there are considerably more risks involved when buying a micro pig over other common pets, such as cats or dogs. The biggest concern is that, since there is no established breed of "teacup pig", there is no guarantee that the pig sold as such will actually stay small. It may be possible to reduce the risk of ending up with a large pig by looking at the pig's parents and grandparents if possible. However, since pigs can breed years before they fully mature, unscrupulous or ignorant breeders may show off parent pigs which are not fully grown themselves, so have not reached their full adult size. Some breeders may falsely claim that a mini-pig is guaranteed to stay under a certain weight, and sometimes will recommend a diet regimen that starves the animal and unnaturally stunts its growth. Pigs need enrichment activities to keep their intelligent minds occupied, if pigs get bored, they often get destructive. 
Some towns and cities have ordinances disallowing farm animals within city limits; a pig is usually considered a farm animal regardless of their size. As well, many small animal vets will not treat pigs. Since these animals have a life span of 15 to 20 years, they require long term commitment. Due to their ability to bond, combined with their need for attention, people who have limited time for a pet may find a pig far more than they can handle. Additionally, if pet pigs are not properly trained when they are young, they can strive for dominance and become aggressive.
There are multiple animal rescue organizations set up to find new homes for pet pigs which have grown too large or otherwise unmanageable for their owners
Other notable references
There are no breeds called teacup or micro or even mini. These are all adjectives and not breeds of pigs.
- John Pukite (1999). A field guide to pigs. ISBN 1-56044-877-6.
- Sachs, DH; Galli, C (2009). "Genetic Manipulation in Pigs". Current Opinion in Organ Transplantation. 14 (2): 148–153. doi:10.1097/mot.0b013e3283292549. PMC . PMID 19469029.
- "Ag Facts: Swine". Oklahoma4h.okstate.edu. 1985-03-05. Retrieved 2016-04-04.
-  - Miniature Potbellied Pig Registry Service,
- The Truth about "Tea Cup" Pigs
- "Is there a "teacup" or "micro" pig?". Mini Pig Info. Retrieved 2016-10-21.
- "History". Miniature Potbellied Pig Registry Service, Inc. Retrieved 4 Feb 2013.
- About Miniature Potbellied Pigs - Miniature Potbellied Pig Registry Service, Inc.
- Mini Pig Care guide
- You must have been told a porky: 'Micro' pig grows to 25 stone and takes over its owners' home By Daily Mail Reporter PUBLISHED: 12:51 EST, 27 July 2012 | UPDATED: 15:00 EST, 27 July 2012
- Minimizing risk when buying a micro pig About Micro Pigs and their size - UK
- Teacup Pigs All the Rage, But Animal Welfare Group Urges People to do Homework Before Taking One Home October 28, 2009
- "Instead of providing breed-appropriate feed and portions, her breeder recommended tiny, toy breed puppy-appropriate food and water bowls." 
- Pot Bellied Pigs as Pets
- Meet Rosie a Yucatan miniature pig May 10, 2009 NECN.com
- Mini pigs are big success on farm 15 October 2007 BBC News
- "Mini Pig Info". Mini Pig Info. Retrieved 2016-10-21.