In China, there is not enough land to grow grass for ruminant animals. However, the crop residues, which are low in degradability and energy content, are abundant. Corn is one of the important economic crops. There are million tons of corn stover (the residue after harvesting corn grains) generated annually. Improving the degradability of corn stover may help to increase its utilization as feed for dairy cows. The first objective of the thesis is identifying the least degradable part of corn stover, which will be treated by fungi as the second objective. Lastly, an optimization model was built to investigate the optimal ratio of plants used as corn stover silage and whole plant corn silage based on the milk production level and the consequences related with methane intensity, nitrogen efficiency and corn saved from using corn stover.