The value of corn stover for Chinese dairy farms

Corn stover is one of the most abundant crop residues in China. Utilization of corn stover as ruminant feed may not only decrease the environmental pollution, caused by burning, but also may improve the profit of dairy farmers, since the price of corn stover is always low. The general objective of the present research was to explore possibilities to improve utilization of corn stover in Chinese dairy farms, including evaluation of consequences of corn stover inclusion in dairy cattle rations for food - feed competition, methane emission, and milk nitrogen (N) efficiency. The least degradable part of corn stover (leaves and stems) was identified first. For most investigated cultivars, the degradation in rumen fluid, as determined by the cumulative gas production technique, showed that the gas production between 3 and 20 h of the leaves, representing cell wall degradability, and the half-time value of leaves, representing rate of cell wall degradation, was greater than that of the stems. Therefore, the cell wall degradation of different internodes from the stem and of internodes harvested during the growing season was studied to find the least degradable part of the stem and to evaluate which factor (lignin content or composition) is most decisive for the cell wall degradation of corn stems. The lignin content and the ratio between syringyl and guaiacyl compounds (S:G ratio) of lignin increased, and the cell wall degradability decreased, from the upper internodes to the lower internodes within the stem of two selected corn cultivars. For corn stems, the S:G ratio showed a better relationship with cell wall degradability in rumen fluid than the lignin content. A lower S:G ratio was accompanied by a higher degradability. Since the lower part of corn stems is less degradable than the upper part, the lower part was chosen to explore whether a fungal treatment or ensiling can enhance the cell wall degradation. Both ensiling and a fungal treatment with Lentinula edodes and Pleurotus eryngii did not improve the degradation of the lower part of the stem of the two corn cultivars. During the ensiling and the fungal treatment, the change in chemical composition was mainly derived from the utilization of water soluble carbohydrates by microorganisms and the degradation of hemicellulose by the fungi. An optimization model was built to determine the ratio of corn plants used as whole plant corn silage and corn stover silage (WPCS:CSS), to maximize the profit of dairy farmers and the consequences with methane emission and milk N efficiency. The optimal WPCS:CSS for dairy farms to maximize their profit increases with greater milk production levels. However, at a fixed total amount of milk being produced, more corn grain will be available for other purposes, including human consumption, with high producing cows fed a diet with an optimal WPCS:CSS. At the optimal WPCS:CSS for each milk production level, methane emission intensity was calculated to be smaller, and milk N efficiency to be greater, with high producing cows compared with low producing cows. Thus, optimizing the use of corn stover in dairy cattle diets improves financial profit of farmers, enables a greater amount of corn grain available for human consumption, and decreases emission of methane and excretion of N in manure of dairy cattle.