Livestock raising contributes about one-third of agricultural income. Livestock fares poorly on the overgrazed pasture, and periods of drought reduce growth on an estimated 20.9 million hectares (51.6 million acres) of permanent pastureland as well as the output of fodder crops. In 2001, estimated livestock population was 17.1 million sheep, 5.2 million goats, and 2.6 million head of cattle. There were an estimated 1,000,000 donkeys, 520,000 mules, 36,000 camels, 8,000 pigs, and 137 million chickens in 2001. In 2001, production of beef and mutton was estimated at 150,000 tons; and poultry, 255,000 tons. Output of cow's milk was about one million tons in 2001, along with 235,000 tons of eggs. Even though most of the import licensing system has been abolished, licenses are still required for imported livestock and animal genetic materials, in an effort to protect local production.