The Hereford is a British breed of beef cattle that originated in the county of Herefordshire, in the West Midlands of England. It has been exported to many countries, and there are more than five million purebred Hereford cattle in over fifty nations worldwide. The Hereford cattle export trade began from United Kingdom in 1817, starting in Kentucky, United States, spreading across the United States and Canada through Mexico to the great beef-raising countries of South America. Today, Hereford cattle dominate the world scene from Australasia to the Russian steppes. They can be found in Israel, Japan and throughout continental Europe and Scandinavia, in the temperate parts of Australia, Canada, the United States, Kazakhstan and Russia, in the centre and east of Argentina, in Uruguay, in Chile and New Zealand, where they make up the largest proportion of registered cattle. They are found all around Brazil and they are also found in some Southern African countries (mainly in South Africa, Zambia and Zimbabwe). They originally found great popularity among ranchers of the American Southwest, testament to the hardiness of the breed; while originating in cool, moist Britain, they have proven to thrive in much harsher climates on nearly every continent. The World Hereford Council is based in the United Kingdom. There are currently 17 member countries with 20 Hereford societies and 10 nonmember countries, with a total of eight societies. In the United States, the official Hereford organization, and breed registry, is the American Hereford Association. It is the second-largest society of its kind in the country. Until the 18th century, the cattle of the Herefordshire area were similar to other cattle of southern England, being wholly red with a white switch, similar to the modern North Devon and Sussex breeds. During the 18th and early 19th centuries, other cattle (mainly Shorthorns) were used to create a new type of draught and beef cattle which at first varied in colour, different herds ranging from yellow to grey and light brown, and with varying amounts of white. However, by the end of the 18th century the white face characteristic of the modern breed was well established, and the modern colour was established during the 19th century. The Hereford is still seen in the Herefordshire countryside today and featured prominently at agricultural shows. The first imports of Herefords to the United States were around 1817 by the politician Henry Clay, with larger importation of the breed beginning in the 1840s. The Polled Hereford is a hornless variant of the Hereford with the polled gene, a natural genetic mutation that was selected into a separate breed beginning in 1889. Iowa cattle rancher Warren Gammon capitalised on the idea of breeding Polled Herefords and started the Polled Hereford registry with 11 naturally polled cattle. The American Polled Hereford Association (APHA) was formed in 1910. The American Polled Hereford and American Hereford breeds have been combined since 1995, under the same American Hereford Association name. Many strains of Hereford have used other cattle breeds to import desired characteristics, and this has led to changes in the breed as a whole. However, some strains have been kept separate, and these have retained characteristics of the earlier breed, such as hardiness and thriftiness. The Traditional Hereford is now treated as a minority breed of value for genetic conservation. Eye cancer (ocular squamous cell carcinoma) occurs in Herefords in particular in countries with continued bright sunlight and those that prefer traits of low levels of red pigmentation around the eye. Studies have been made into eye cancer in Hereford cattle in the US and Canada, and lid and corneoscleral pigment were found to be heritable and likely to decrease the risk of cancer. Vaginal prolapse is considered a heritable problem in Hereford cattle, but it may also be influenced by nutrition. Another problem is exposed skin on the udder being of light pigmentation and therefore vulnerable to sun burn.