Effects of Pennisetum purpureum and Pennisetum sinese proportions on in vitro rumen fermentation characteristics of goats

The effects of different proportions of Pennisetum purpureum (PP) and Pennisetum sinese (PS) on rumen fermentation characteristics in Leizhou goats were studied using an in vitro gas production technique. Results of this study will provide references for the production of formula feed in South China. According to the dry substance ratio, PP and PS were mixed in ratios of 100∶0, 75∶25, 50∶50, 25∶75, 0∶100 and separated into groups T₁, T₂, T₃, T₄, and T₅, respectively. Samples in groups T₁, T₂, T₃, T₄, and T₅ were cultured for 4, 8, 12, 24, and 48 hours, respectively. Triplicates were used for each group and three blank controls were used for each time point. Microbial fermentation stopped at the end of the culturing period. We determined organic matter degradability (OMD) and crude fibre degradability (CFD) in fermentation residue. We also measured acetic acid, propionic acid, butyric acid concentrations and acetic acid and propionic acid ratios in fermentation liquor. The single factor associative effects index (SFAEI) and multiply factors associative effects index (MFAEI) were calculated. Results showed that OMD increased gradually as PS increased in every group, with markedly higher increases observed for T₃, T₄ and T₅ groups relative to the T₁ group (P < 0.05). No significant differences were observed for in vitro fermentation after 48 hours for T₃ and T₄ groups (P > 0.05). CFD showed no significant differences between T₃ and T₄ groups and T₁ and T₅ groups at 48 hours of fermentation (P > 0.05). OMD and CFD significantly increased from 12 to 48 h of in vitro fermentation in each group (P < 0.05). After 48 hours, the proportion of acetic acid in T₄ was significantly lower than in other groups (P < 0.05). The proportion of propionic acid was significantly higher than in T₂ after 48 hours (P < 0.05), while no significant difference was observed for T₃ (P > 0.05). The proportion of butyric acid in T₄ was significantly higher than that of other groups (P < 0.05). Additionally, the ratios of acetic acid and propionic acid in T₃ and T₄ ranged from 2.71 to 3.50 after 8 to 48 h of fermentation are normal levels. The highest observed MFAEI was 1.68, which occurred when proportion of PP and PS was 25∶75. In conclusion, the optimal ratio of PP and PS was determined to be 25∶75.