添加糖蜜和乙酸对西藏发酵全混合日粮青贮发酵品质及有氧稳定性影响

摘要

为研究乙酸和糖蜜对发酵全混合日粮（FTMR）品质及有氧稳定性的影响，试验以全混合日粮（TMR）为发酵原料，设对照组、乙酸（A）、糖蜜（M）、乙酸和糖蜜组合添加（AM）4个处理，发酵45 d 后分析 FTMR 的发酵品质，同时将所有 FTMR 暴露到空气中，分别在第6，9和12天取样评定其有氧稳定性。结果表明，与对照相比，A 和 AM组降低了乳酸含量（P ＞0．05），各组仅检测到微量的丙酸、少量的丁酸和较低的氨态氮／总氮，表明各组 FTMR 发酵品质均良好。有氧暴露6 d 后，各组乳酸、乙酸和水溶性碳水化合物含量均呈不同程度的下降，对照和 M 组 pH值在第12天显著（P ＜0．05）上升至5．70和6．50，具有较高的氨态氮／总氮和酵母菌数量。而 A 和 AM 组乳酸含量均呈先上升后下降的变化趋势，且好氧性微生物和酵母菌数量在整个有氧暴露的过程中始终维持在较低水平，有氧暴露12 d 后 pH 值仍维持在4．50左右，延长了有氧稳定时间。综合考虑，为了获得品质优良的 FTMR 饲料，可在 TMR 中添加0．3％乙酸，既不影响发酵品质，也可提高其有氧稳定性。%An experiment was undertaken to study the effects of acetic acid or/and molasses on the quality of fermented total mixed ration silage.Treatments:silage fermented without additive (control),with acetic acid (0.3% fresh matter basis),with molasses (3% fresh matter basis),or with acetic acid+molasses.There were 20 silos per treatment.All silos were opened 45 d after ensiling;five silos per treatment were analysed to deter-mine fermentation characteristics,the remaining silos were exposed to air for 12 d to evaluate aerobic stability. After 45 dall silages were of good quality having high lactic acid concentration,low ammonia/total nitrogen, low butyric acid and very little propionic acid.During aerobic exposure,lactic acid,acetic acid and water solu-ble carbohydrate tended to decrease in all silages.The pH of the control and molasses treated silages increased significantly to 5.70 and 6.50 respectively and ammonia/total nitrogen and yeast counts were higher than the acetic acid and acetic acid+molasses treatments after 12 days of exposure.However,adding acetic acid reduced ammonia/total nitrogen compared with the control.Lactic acid content in the acetic acid and acetic acid+mo-lasses silages increased during the early stages of aerobic exposure and then slowly decreased.Undesirable bac-teria and yeast counts in the acetic acid treatment remained at low levels during aerobic exposure and the pH re-mained at about 4.50.It is concluded that adding 0.3% acetic acid maintained fermentation quality and im-proved the aerobic stability of fermented total mixed ration silage.