The raising of livestock, traditionally a supplementary occupation among ROK farmers, expanded rapidly during the 1970s and 1980s. In 2001, 1.9 million head of cattle were raised; pigs totaled 8,719,000, and chickens, 102 million. Production in 2001 included (in thousands of tons): beef, 226; pork, 928; chicken, 433; eggs, 522; milk, 2,338; butter, 5.7. The silkworm industry has declined radically since the mid-1970s. Although the dairy industry has been protected by import restrictions, an incremental lifting of such trade constraints is underway, which will eventually include livestock imports.