Effects of mixed silage containing corn straw and rape on the in vitro fermentation characteristics of rumen fluid from Tan sheep

The objective of this study was to evaluate the effects of dietary supplementation with rape on the in vitro fermentation of rumen fluid from Tan sheep. Rape, which has a high water content, was mixed with yellow corn straw in various ratios to produce silage containing 50%, 55%, 60%, 65%, and 70% moisture; unmixed yellow corn straw was used as the control group. Samples underwent 60 days of in vitro fermentation in sealed containers containing rumen fluid from Tan sheep, with three repeats in each group, after which they were analyzed. The results showed that the dry matter digestibility (DMD) increased with the proportion of rape (P < 0.05); the lowest DMD was 48.01% in the control group, and the highest DMD was 66.81% in the 70% moisture group. There was no significant difference in neutral detergent fiber digestibility between groups ( P > 0.05). Gas production was significantly higher in the experimental groups than in the control group ( P < 0.05), but there was no significant difference among the five experimental groups ( P > 0.05). There were no significant differences between groups in terms of pH value, ammonia–nitrogen (NH ₃-N) concentration, total volatile fatty acid concentration, or levels of acetic, propionic, butyric, isobutyric, or isovaleric acids (P > 0.05). In conclusion, the silage mix with 70% moisture content (79.45∶20.55 ratio of rape to corn straw) had the best effects on in vitro fermentation. However, the ideal proportion of rape to be included in mixed silage for Tan sheep needs to be determined using feeding experiments.