RESUMO
Two experiments were carried out to determine the optimal proportion of mixed silage made with wheat straw and tall fescue, and further to evaluate the effects of molasses on fermentation quality. In Experiment 1, wheat straw and tall fescue were mixed at proportions of 10:0 (Control), 8:2 (WT20), 6:4 (WT40) and 4:6 (WT60) on fresh weight (FW) basis. Inclusion of tall fescue significantly (p < 0.05) increased lactic acid, water-soluble carbohydrate contents and ratio of lactic to acetic acid, and significantly (p < 0.05) decreased pH and contents of dry matter, NH3 -N and volatile fatty acids. WT60 had the highest (p < 0.05) lactic acid content, and the lowest (p < 0.05) pH and butyric acid content. In Experiment 2, the mixture of wheat straw and tall fescue (4/6) were treated with 0%, 3%, 4% and 5% molasses on FW basis (defined as control, WTM3, WTM4 and WTM5 respectively). Molasses addition significantly (p < 0.05) increased lactic acid and water-soluble carbohydrate contents, and significantly (p < 0.05) decreased pH and ammonia-nitrogen content as compared with control. Acetic acid content slightly (p > 0.05) decreased during ensiling, while trace amounts of propionic and butyric acids were observed. WTM5 had the lowest pH and the highest (p < 0.05) lactic acid, water-soluble carbohydrate contents and ratio of lactic to acetic acid at end of ensiling. In conclusion, the fermentation quality was maximally improved when the addition rate of molasses was 5% in 40% wheat straw ensiled with 60% tall fescue.