In 2001, Dominican livestock included 187,000 goats and 106,000 sheep. There were also about 2.1 million head of cattle, 60% for beef and 40% for dairy. The hog population was decimated by African swine fever, decreasing from 400,000 in 1978 to 20,000 in 1979; by 2001, however, it was 565,000. Poultry is the main meat source because it is cheaper than beef or pork. Poultry production relies on imports of feed grain from the United States. In 2001, 203,000 tons of poultry meat were produced, along with 71,000 tons of beef and 420,000 tons of milk.
Question: By how many heads did the hog population decrease from African swine fever from 1978 to 1979?
Answer: 180000