Evaluation of the nutritive value and in vitro digestibility of forage sorghum

The aim of this study was to investigate the changes in nutritional value of four sorghum varieties of Hainiu, Big kahuna, Dajiang 3180, and Dajiang 1180 at different stages of development, in the Hexi saline-alkali area of Gansu Province. The main nutrient components, in vitro digestibility, and in vitro fermentation gas production of the four varieties during branching period, jointing stage, and heading stage were determined by proximate analysis and in vitro gas production techniques. The results showed that the height and fresh weight of the four varieties were significantly different. Furthermore, a significant increase in the height and fresh weight of the four varieties was observed (P>0.05). The results also revealed that the fresh weight and ratio of stems to leaves of Hainiu was the highest, while those of Dajiang 1180 were the lowest with prolonged harvest. Further, the crude protein content in different parts of the same species was also different, in the order stem<whole plant<leaves. The NDF and ADF decreased significantly (P<0.05). The NDF and ADF of Hainiu and Big kahuna were significantly lower at the jointing and heading stages than those of the other two cultivars. The higher NDF and ADF positively affected the relative feeding value. At the same time, the stalks, leaves, and whole plants of Hainiu and Big kahuna also contained high sugar contents. The gas production, VFA concentration, and dry matter disappearance rate of Hainiu and Big kahuna was higher than those of the other two cultivars at 72 h. There were no significant differences in the yield of methane among the four varieties. The results suggest that Hainiu and Big kahuna are the best forage varieties with high nutritional and feeding values. Thus the varieties can be recommended for large-scale planting on dry saline lands of Hexi, Gansu.