This graph shows the rise and fall of pig farming in New Zealand. Until the mid-20th pig farming was closing associated with dairy farming, since the pigs were fed on the skim milk and whey left over from making butter and cheese. As dairying expanded in the first part of the 20th century, pig numbers rose fast to reach a peak in the mid-1930s. However, as milk processing moved to large dairy factories, fewer pigs were kept on dairy farms. There was a revival the 1950s and early 1960s as pig farming moved to the grain areas of the South Island, as pigs generally were fed grain, but since then tough international competition and the increased use of land for irrigated dairy farms has led to a steady decline in the number of pig farms.