Departamento de Producción Animal, Universidad de León, 24007 León, Spain.
J Dairy Sci. 2010 Aug;93(8):3684-98. doi: 10.3168/jds.2009-2933.
Four ruminally and duodenally cannulated sheep and 8 Rusitec fermenters were used to determine the effects of forage to concentrate (F:C) ratio and type of forage in the diet on ruminal fermentation and microbial protein synthesis. The purpose of the study was to assess how closely fermenters can mimic the dietary differences found in vivo. The 4 experimental diets contained F:C ratios of 70:30 or 30:70 with either alfalfa hay or grass hay as the forage. Microbial growth was determined in both systems using (15)N as a microbial marker. Rusitec fermenters detected differences between diets similar to those observed in sheep by changing F:C ratio on pH; neutral detergent fiber digestibility; total volatile fatty acid concentrations; molar proportions of acetate, propionate, butyrate, isovalerate, and caproate; and amylase activity. In contrast, Rusitec fermenters did not reproduce the dietary differences found in sheep for NH(3)-N and lactate concentrations, dry matter (DM) digestibility, proportions of isobutyrate and valerate, carboxymethylcellulase and xylanase activities, and microbial growth and its efficiency. Regarding the effect of the type of forage in the diet, Rusitec fermenters detected differences between diets similar to those found in sheep for most determined parameters, with the exception of pH, DM digestibility, butyrate proportion, and carboxymethylcellulase activity. Minimum pH and maximal volatile fatty acid concentrations were reached at 2h and at 6 to 8h postfeeding in sheep and fermenters, respectively, indicating that feed fermentation was slower in fermenters compared with that in sheep. There were differences between systems in the magnitude of most determined parameters. In general, fermenters showed lower lactate concentrations, neutral detergent fiber digestibility, acetate:propionate ratios, and enzymatic activities. On the contrary, fermenters showed greater NH(3)-N concentrations, DM digestibility, and proportions of propionate, butyrate, isovalerate, valerate, and caproate. Values of efficiency of microbial growth were greater in fermenters compared with sheep for 70:30 diets, but they were lower for 30:70 diets. Differences between fermentation in sheep and fermenters can be mainly attributed to the lack of absorption in fermenters, differences in solid retention time, and compartmentalization in the Rusitec system. In general, the Rusitec system simulated more closely the in vivo fermentation of high-forage diets compared with high-concentrate diets.
本试验旨在评估发酵罐在多大程度上可以模拟体内发现的饮食差异，使用 4 头安装有瘤胃和十二指肠瘘管的绵羊和 8 个鲁塞尔（Rusitec）发酵罐，研究饲粮中粗饲料与精饲料的比例和粗饲料种类对瘤胃发酵和微生物蛋白合成的影响。这 4 种试验饲粮的粗饲料与精饲料的比例分别为 70:30 或 30:70，粗饲料分别为紫花苜蓿干草或羊草。采用（15）N 作为微生物标记物，在这两种系统中测定微生物的生长情况。与绵羊相比，改变 pH 值、中性洗涤纤维消化率、总挥发性脂肪酸浓度、乙酸、丙酸、丁酸、异丁酸和己酸的摩尔比例以及淀粉酶活性，鲁塞尔发酵罐可以检测到不同饲粮之间的差异。相反，鲁塞尔发酵罐无法复制绵羊饲粮中发现的氨态氮（NH3-N）和乳酸浓度、干物质（DM）消化率、异丁酸和戊酸比例、羧甲基纤维素酶和木聚糖酶活性以及微生物生长及其效率的差异。关于饲粮中粗饲料种类的影响，除了 pH 值、DM 消化率、丁酸比例和羧甲基纤维素酶活性外，鲁塞尔发酵罐检测到的饲粮间差异与绵羊的相似。绵羊和发酵罐的最小 pH 值和最大挥发性脂肪酸浓度分别在饲喂后 2h 和 6-8h 达到，这表明与绵羊相比，发酵罐中的饲料发酵较慢。在大多数测定参数方面，系统之间存在差异。一般来说，发酵罐中的乳酸浓度、中性洗涤纤维消化率、乙酸：丙酸比例和酶活性较低。相反，发酵罐中的 NH3-N 浓度、DM 消化率以及丙酸、丁酸、异丁酸、戊酸和己酸的比例较高。与绵羊相比，70:30 饲粮的发酵罐微生物生长效率较高，但 30:70 饲粮的发酵罐微生物生长效率较低。绵羊和发酵罐发酵之间的差异主要归因于发酵罐缺乏吸收、固体保留时间的差异以及鲁塞尔系统的分隔化。一般来说，与高精料饲粮相比，鲁塞尔系统更能模拟高粗料饲粮的体内发酵。
