Effects of molasses on the fermentation characteristics of mixed silage prepared with rice straw, local vegetable by-products and alfalfa in Southeast China

This experiment was conducted to study the effect of molasses on the fermentation characteristics of mixed silage ensiled rice straw and vegetable by-products with alfalfa. Mixture (202 g kg−1 dry matter (DM)) consisting of rice straw, broccoli residue and alfalfa at the ratio of 5:4:1 was ensiled with three experimental treatments: (1) no additives (control); (2) molasses at 2.5% (M1); (3) molasses at 5% (M2) on a fresh matter basis of mixture, respectively. All treatments were packed into laboratory-scale silos, and three silos per treatment were sampled on days 1, 3, 5, 14 and 30. The result showed that the pH value of all mixed silages decreased gradually with the time of ensiling except for the control silage, in which a significant increase (P <0.05) on day 30 occurred. The lactic acid content increased gradually with the time of ensiling and reached the highest value on day 14, and a marked decrease (P <0.05) was found in the control silage on day 30. The changes of acetic acid content showed similar pattern with lactic acid content. A trace amount of propionic and butyric acid contents were found in the three mixed silages during the fermentation period. Comparing to the control, M1 and M2 treatments improved the fermentation quality of mixed silages as indicated by higher (P <0.05) lactic acid contents and lower (P <0.05) pH and ammonia-N contents. The Flieg points also showed that M1 and M2 silages were well preserved, whereas the control silage had a bad quality. Overall, the findings of this study suggested that adding molasses could improve fermentation quality of mixed silage, and M1 was more suitable for practical application.