西藏不同饲草全混合日粮发酵品质和有氧稳定性的研究

摘要

The objective of this study was to identify opportunities to improve the utilization of crop straw and forage resources in Tibet.The experiment was based on the total mixed ration (TMR)typically used in local dairy systems,comprising whole-crop corn and barley straw (TMR-1 ),comparing substitutes for whole-crop corn;alfalfa (TMR-2),whole-crop oat (TMR-3)or wheat straw (TMR-4)at different ratios.After 45 d fer-mentation,pH values of TMR-2,TMR-3 and TMR-4 treatments were significantly (P <0.05 )higher than that of TMR-1,while corresponding lactic acid contents were lower.Propionic acid and butyric acid were very low in all treatments except TMR-1 and ammonia nitrogen/total nitrogen was <100 g/kg TN,indicating that fermentation was good in all treatments.Water-soluble carbohydrate content in all treatments was significantly lower (P <0.05)after 45 d of fermentation.The dry matter content of all treatments except TMR-1 remained constant,while crude protein,neutral detergent fiber,acid detergent fiber and ether extract increased in all treatments.The crude protein content of TMR-2 and TMR-3 were above 15%,sufficient for dairy production. During aerobic exposure,lactic acid,acetic acid and water-soluble carbohydrate content of all treatments de-clined.Propionate and butyrate content initially increased after three days of aerobic exposure and then gradual-ly decreased in all treatments.After 9 d of aerobic exposure,the pH increased but the increase was minimal in TMR-3,indicating good aerobic stability.It was concluded that TMR-3 group could be used to produce TMR in Tibet.%为了充分利用西藏的农作物秸秆和饲草资源，本试验在当地奶牛场采用的以全株玉米和青稞秸秆为主要粗饲料的 TMR 配方基础上，用苜蓿、全株燕麦和小麦秸秆按不同比例替代全株玉米。青贮发酵45 d 后评定各组发酵品质、营养特性和有氧稳定性。结果表明，发酵45 d 后，TMR-2、TMR-3和 TMR-4组 pH 值显著高于 TMR-1（P ＜0．05），乳酸含量均低于 TMR-1，但各替代组仅检测到微量丙酸和丁酸含量，且氨态氮／总氮较低，表明各组发酵品质均良好。发酵后各组水溶性碳水化合物含量均有大幅度下降，除 TMR-1组外，其他3组干物质含量基本不变，粗蛋白、中性洗涤纤维、酸性洗涤纤维和粗脂肪等营养物质含量不同程度增加，其中 TMR-2和 TMR-3组粗蛋白含量高于15％，能够满足改良奶牛的营养需要。在有氧暴露过程中，各组乳酸、乙酸和水溶性碳水化合物含量均出现不同程度的下降，丙酸和丁酸含量在有氧暴露第3天均有升高，之后逐渐下降。在有氧暴露9 d 中，pH 值均呈上升趋势，其中 TMR-3组 pH 值上升幅度最小，其有氧稳定性最好。综上所述，虽然 TMR-3发酵品质略低于TMR-1组，但其有氧稳定性有所提高，因此，TMR-3组可应用于生产实际中。