Effects of Different Growth Stages of Amaranth Silage on the Rumen Degradation of Dairy Cows

The purpose of this study was to investigate the rumen degradation characteristic of amaranth silage (Amaranthus hypochondriacus) including four kinds of growing stages (budding stage (BS), 50 d after planting (DAP); early flowering stage (ES), 58 DAP; peak flowering stage (PS), 70 DAP; heading stage (HS), 90 DAP). Four Holstein dairy cows with permanent ruminal cannulas were used as experimental animals. Nylon-bag method was used to assess the ruminal degradability of dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF). The results showed that the concentration of DM in HS was significantly higher than other stages (p < 0.05), whereas the contents of CP, were lower than in other stages (p < 0.05). With the extension of the growing period, the DM effective degradability of amaranth silage decreased gradually, and the difference was significant (p < 0.05). The ruminal CP degradation of 72 h was more than 80%, and compared with ES and HS, the degradation rate of BS and PS was significantly increased (p < 0.05). Compared to BS, the effective degradability of CP was increased (p < 0.05) in ES and HS. For ruminal NDF degradability, the effective degradability of HS was minimum, and it had a noticeable difference with BS and ES (p < 0.05). Thus, the different quality of amaranth growth stage including chemical contents and rumen degradation should be taken into consideration when making amaranth silage. In the present study, the optimal growth stage of amaranth was from the peak flowering stage to heading stage for ensiling.