A teacup pig is one of the breeds developed and used for medical research or developed for use as a pet. These smaller pigs were first used for medical research in Europe before being introduced to the United States as pets in the 1980s. Since then, the animals have been used in studies by scientists around the world, including for study as a source of organs for organ transplantation. Some miniature pigs are also kept as pets in European countries.
Vietnamese pot-bellied pigs that grow to be 150–200 pounds (68–91 kg) were sent to zoos in Western nations in the 1960s. In the mid-1980s, Keith Connell of the Bowmanville, Ontario zoo imported twenty breeders to Canada. Two of the pigs died in quarantine. The remaining 18 unrelated pigs were the foundation for the Potbellied Pig in North America. Because of the customs laws, only the offspring could be sold to 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 help 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. These pigs average 150–200 lbs. 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 also met the breed standard of less than 15 inches tall. All of the foundation pigs were dually registered in PPRSI and MPPRSI.
In the UK, British micro pigs have been bred by Rob Rose in Cumbria since 1996.These pigs are a cross between KuneKune pigs (a New Zealand pig that weighs around 200 pounds (91 kg)), Gloucester Old Spots (800 lbs), and Tamworths (800 pounds (360 kg)). After several generations of crossing, the pigs have been marketed as truly tiny pigs that work well as pets. They have not been bred long enough to be considered a true breed and are not a consistent size or shape. After the initial press releases, breeders began popping up all over Britain trying to push pocket-piglets which later became genuine hogs unfit for suburban dwelling. British micro pigs are not only found in zoos, animal parks and open farms, but are also kept as pets.
There are breeders who are selling “miniature” pigs that are simply immature. Newborn piglets can be as small as 4 ounces (110 g) and easily fit in a teacup, but will not stay tiny. Because potbellied pigs don’t reach their mature size until they are three years old but can breed as early as three months, some unscrupulous breeders are selling newborn piglets born to immature parents and claiming the babies will stay small. It is important for any potential owner to check out the parents and adult siblings and only choose reputable breeders who have years of experience.