The I is a traditional Vietnamese breed. It is thought to have originated in the
province of
Nam Định, in the
Red River Delta. It was the dominant local pig breed in most provinces of the delta, and was widely distributed in Nam Định province and the neighbouring provinces of
Hà Nam,
Ninh Bình and
Thái Bình, as well as in the province of
Thanh Hóa immediately to the south, in the
North Central Coast region. Until the 1970s the I was probably the most numerous pig breed in northern Vietnam, with numbers running into millions. From that time, the more productive
Móng Cái began to supplant it. The
National Institute of Animal Husbandry of Vietnam started a conservation programme, with subsidies for farmers who reared
purebred stock, but this had little benefit – there was some increase in numbers, but at the cost of increased
inbreeding. In 1991, the total population of the I was estimated at , and by 2010 the estimated number was 120; no population data was reported in the following fifteen years. In 2003 the National Institute of Animal Husbandry listed its
conservation status as "critical" and in 2007 the
Food and Agriculture Organization of the United Nations listed it as "endangered"; in 2025 its
conservation status was unknown. Small numbers of I pigs were exported in the 1960s to Canada and Sweden, to be kept in zoos or to be used for laboratory experiments. Within a decade, the I had spread to animal parks in other countries in Europe; a few were reared on
smallholdings. The I entered the United States from Canada in the mid-1980s, and by the end of the decade the "pot-bellied pig" was being marketed as a pet. Not all of these were purebred, and some grew to considerable size; the fad was short-lived. In 2013 it was declared an
invasive species in
Spain. == Characteristics ==