Pourazad P, Khiaosa-Ard R, Metzler-Zebeli B U, Klevenhusen F, Zebeli Q
1Department for Farm Animals and Veterinary Public Health,Institute of Animal Nutrition and Functional Plant Compounds,University of Veterinary Medicine Vienna,1210 Vienna,Austria.
2Department for Farm Animals and Veterinary Public Health,University Clinic for Swine,University of Veterinary Medicine Vienna,1210 Vienna,Austria.
Animal. 2017 Dec;11(12):2193-2202. doi: 10.1017/S1751731117001112. Epub 2017 May 22.
In this study, we used two different grain-rich feeding models (continuous or transient) to determine their effects on in situ fiber degradation and abundances of important rumen fibrolytic microbes in the rumen. The role of the magnitude of ruminal pH drop during grain feeding in the fiber degradation was also determined. The study was performed in eight rumen-fistulated dry cows. They were fed forage-only diet (baseline), and then challenged with a 60% concentrate diet for 4 weeks, either continuously (n=4 cows) or transiently (n=4 cows). The cows of transient feeding had 1 week off concentrate in between. Ruminal degradation of grass silage and fiber-rich hay was determined by the in situ technique, and microbial abundances attached to incubated samples were analyzed by quantitative PCR. The in situ trials were performed at the baseline and in the 1st and the last week of concentrate feeding in the continuous model. The in situ trials were done in cows of the transient model at the baseline and in the 1st week of the re-challenge with concentrate. In situ degradation of NDF and ADF of the forage samples, and microbial abundances were determined at 0, 4, 8, 24 and 48 h of the incubation. Ruminal pH and temperature during the incubation were recorded using indwelling pH sensors. Compared with the respective baseline, both grain-rich feeding models lowered ruminal pH and increased the duration of pH below 5.5 and 5.8. Results of the grass silage incubation showed that in the continuous model the extent of NDF and ADF degradation was lower in the 1st, but not in the last week compared with the baseline. For the transient model, degradation of NDF of the silage was lower during the re-challenge compared with the baseline. Degradation of NDF and ADF of the hay was suppressed by both feeding models compared with the respective baseline. Changes in fiber degradation of either grass silage or hay were not related to the magnitude of ruminal pH depression during grain-rich feeding. In both feeding models total fungal numbers and relative abundance of Butyrivibrio fibrisolvens attached to the incubated forages were decreased by the challenge. Overall, Fibrobacter succinogenes was more sensitive to the grain challenge compared with Ruminococcus albus and Ruminococcus flavefaciens. The study provided evidence for a restored ruminal fiber degradation after prolonged time of grain-rich feeding, however depending on physical and chemical characteristics of forages.
在本研究中，我们使用了两种不同的富含谷物的饲养模式（持续或短暂）来确定它们对瘤胃原位纤维降解以及瘤胃中重要瘤胃纤维分解微生物丰度的影响。还确定了谷物饲养期间瘤胃液pH值下降幅度在纤维降解中的作用。该研究在八头装有瘤胃瘘管的干奶牛身上进行。它们先仅饲喂草料日粮（基线），然后连续4周（n = 4头奶牛）或短暂地（n = 4头奶牛）用60%精料日粮进行挑战。短暂饲养的奶牛在中间有1周不喂精料。通过原位技术测定青贮草和富含纤维的干草的瘤胃降解情况，并通过定量PCR分析附着在培养样品上的微生物丰度。原位试验在连续模式的基线期以及精料饲喂的第1周和最后1周进行。原位试验在短暂模式的奶牛的基线期以及再次用精料挑战的第1周进行。在培养的0、4、8、24和48小时测定饲草样品中中性洗涤纤维（NDF）和酸性洗涤纤维（ADF）的原位降解情况以及微生物丰度。使用植入式pH传感器记录培养期间的瘤胃液pH值和温度。与各自的基线相比，两种富含谷物的饲养模式均降低了瘤胃液pH值，并增加了pH值低于5.5和5.8的持续时间。青贮草培养结果表明，在连续模式中，与基线相比，第1周NDF和ADF的降解程度较低，但最后一周并非如此。对于短暂模式，与基线相比，再次挑战期间青贮料NDF的降解较低。与各自的基线相比，两种饲养模式均抑制了干草中NDF和ADF的降解。青贮草或干草纤维降解的变化与富含谷物饲养期间瘤胃液pH值下降幅度无关。在两种饲养模式中，挑战均使附着在培养饲草上的真菌总数和溶纤维丁酸弧菌的相对丰度降低。总体而言，与白色瘤胃球菌和黄色瘤胃球菌相比，产琥珀酸丝状杆菌对谷物挑战更敏感。该研究为长期富含谷物饲养后瘤胃纤维降解的恢复提供了证据，不过这取决于饲草的物理和化学特性。
