Although not a cash crop like potatoes and beets, corn has become increasingly valuable in North Dakota. This is especially true in the southeastern part of the State, which is the hog-raising area of North Dakota. During the five-year period of 1927-31, the average annual corn production was 20,200,000 bushels. Only in rare instances does North Dakota corn reach the cash markets. It is not husked as in many of the Corn Belt States; instead, the hogs and sometimes the cattle are permitted to feed directly on the stocks in the field. This is known as the "hogging down" method of harvesting corn. About one-half the crop is cut annually for winter fodder. Other feed crops are also important on the North Dakota farm. Many hay and pasture crops, especially red clover and alfalfa, can be successfully grown in the Red River Valley. In the western sections, alfalfa is raised for seed. Timothy and brome grass are also valuable grass crops in the eastern area. In 1914 sweet clover was cultivated only on demonstration farms; but by 1929 an average of more than half a million acres was being seeded annually. Each year production of seed increased, reaching a high of 171,600 bushels in 1933. Sweet clover replaces nitrogen and other essential elements in soil which has been badly depleted by overproduction of wheat. One remarkable feature of this crop is its immunity to disease and insect pests. Sheep are found generally throughout the State, although the northern part of the Red River Valley and the southwestern corner of the Missouri Slope have proved the best sheep-raising land. The animals were brought into the State when ranching first began here, and in 1933 there were 706,000 head of sheep and lambs shipped out of the State and 15,000 slaughtered locally. In 1935 North Dakota ranked twenty-second in the number of sheep on farms and ranges. A true picture of cattle-raising in North Dakota can scarcely be gained from present conditions. The native grasses of the western part of the State were unable to withstand the heat and insects of recent dry years. As an emergency measure, thousands of cattle were shipped from western ranches to farms in the eastern and central part of the State, and even to other sections of the country where sufficient feed was available to carry them through the winter. The number of cattle and calves was reduced from 1,835,000 in 1934 to 1,157,000 in 1935. The decrease in milk cows, since they are raised in the less arid sections of the State, has been much less than that in beef cattle. In 1934 there were 620,000 milk cows, while in 1935 the number was 596,000--a drop of only 24,000. Thus, despite reverses, North Dakota was able to maintain a position as twenty-first in the Nation in the cattle census of 1935.