Effects of wheat bran supplementation on the quality of mixed silage from feed rape and corn straw

The carbon source is an important factor that affects the fermentation quality of silage. The present study was conducted to investigate the effects of wheat bran addition as a carbon source on the quality of mixed feed rape and corn straw silage. Fresh feed rape and corn straw were evenly mixed at a proportion of 2∶1. Wheat bran, with a humidity 60%, was then added as the carbon source at 0, 2%, 4%, 6%, 8%, and 10%. The pH value of the mixed silage was measured on the 3^rd, 7^th, 15^th, 23^rd, 30^th, 45^th, and 60^th days. The evaluations of the sensory characteristics, main nutrient contents, and fermentation index were performed on the 60^th day. The results demonstrated that the fermentation quality of feed rape and corn straw silage with wheat bran improved remarkably after 60 days, and the sensory scores were all higher than 13 points. The pH values of each group decreased significantly (P < 0.05), with the fastest reduction before 7 days. The pH value of each group decreased to below 4.25 by the end of the experiment. Nutrient analysis found that the CP, EE, and ash contents in the group with 10% wheat bran addition was significantly higher than those in the other groups (P < 0.05). Meanwhile, the NDF and ADF contents in the group with 10% wheat bran were significantly lower than those in the other groups (P < 0.05). The analysis of the fermentation parameters showed that the ammonia nitrogen content and proportion of ammonia nitrogen in the total nitrogen in the 10% wheat bran group were significantly lower than those in the other groups (P < 0.05). The ammonia nitrogen in the total nitrogen reached the highest ratio of 6.09% in the 0 wheat bran group. Meanwhile, there were also significant intergroup differences concerning the lactic acid content (P < 0.05), with the maximum lactic acid content of 89.83 g·kg⁻¹ being reached in the 10% group. The analysis of the volatile fatty acid composition demonstrated that acetic acid was the most abundant in each group, while no butyric acid was detected. There were significant intergroup differences for both acetic and propionic acids (P < 0.05). The acetic acid content in the 0 addition group reached 19.02 g·kg⁻¹. The propionic acid content in the 10% addition group reached 0.87 g·kg⁻¹. In summary, the addition level of wheat bran significantly influences the quality of mixed rape and corn straw silage. High quality silage can be obtained with the addition of wheat bran at 10%.