USDA-ARS, US Dairy Forage Research Center, Madison, WI 53706, USA.
J Dairy Sci. 2010 Jan;93(1):265-78. doi: 10.3168/jds.2009-2206.
Eighteen ruminally cannulated dairy cattle were fed a series of diets (in 28-d periods) designed to elicit different degrees of milk fat depression (MFD) for the purpose of relating MFD to ruminal bacterial populations. Cows were fed a TMR containing 25% starch (DM basis) supplied as corn silage, a slowly fermented starch (SFS treatment, period 1), then switched to a TMR containing 27% starch, much of it supplied as ground high-moisture corn, a rapidly fermented starch (RFS treatment, period 2). In period 3, the RFS diet was amended with 13.6 mg of monensin/kg of DM (RFS/Mon treatment), and in period 4, the cows were returned to the RFS diet without monensin (RFS/Post treatment). Effect of both starch source and monensin on milk fat percentage varied by cow, and cluster analysis identified 4 pairs of cows having distinct milk fat patterns. Archived ruminal liquors and solids from the 4 pairs were processed to isolate bacterial DNA, which was subjected to automated ribosomal intergenic spacer analysis followed by correspondence analysis to visualize bacterial community composition (BCC). One pair of cows (S-responsive) showed MFD on RFS feeding, but displayed no additional MFD upon monensin feeding and a fat rebound upon monensin withdrawal. The second pair of cows (M-responsive) showed no MFD upon switch from the SFS diet to the RFS diet, but displayed strong MFD upon monensin feeding and no recovery after monensin withdrawal. Both groups displayed major shifts in BCC upon dietary shifts, including dietary shifts that both did and did not change milk fat production. The third pair of cows (SM-responsive) displayed reduction of milk fat on both RFS and RFS/Mon diets, and fat returned to the levels on the RFS diet upon monensin withdrawal; these cows showed a more gradual shift in BCC in response to both starch source and monensin. The fourth pair of cows (nonresponsive) did not display changes in milk fat percentage with dietary treatment and showed only minor shifts in BCC with dietary treatment. Regardless of milk fat response, BCC did not reassemble its original state upon monensin withdrawal, though the difference was strongest in M-responsive cows. One amplicon length (representing a single bacterial species) was elevated in most, but not all, MFD-susceptible (S-, M-, or SM-responsive) cows relative to milk fat-nonresponsive cows, whereas 2 amplicon lengths displayed reduced abundance under MFD conditions. Overall, this study demonstrates an association between MFD and wholesale shifts of microbial communities in the rumen.
十八头瘤胃内置有套管的奶牛被喂食一系列的饲料（28 天为一个周期），这些饲料旨在引起不同程度的乳脂下降（MFD），以便将 MFD 与瘤胃细菌种群联系起来。奶牛被喂食含有 25%淀粉（DM 基础）的 TMR，这些淀粉来自玉米青贮饲料，是一种缓慢发酵的淀粉（SFS 处理，第 1 期），然后切换到含有 27%淀粉的 TMR，其中大部分来自磨碎的高水分玉米，这是一种快速发酵的淀粉（RFS 处理，第 2 期）。在第 3 期，RFS 日粮中添加了 13.6 毫克莫能菌素/千克 DM（RFS/Mon 处理），在第 4 期，奶牛被喂回不含莫能菌素的 RFS 日粮（RFS/Post 处理）。淀粉来源和莫能菌素对乳脂百分率的影响因牛而异，聚类分析确定了 4 对具有明显乳脂模式的奶牛。从这 4 对牛的存档瘤胃液和固体中提取细菌 DNA，对其进行自动化核糖体基因间 spacer 分析，然后进行对应分析，以可视化细菌群落组成（BCC）。有一对奶牛（S 反应型）在喂 RFS 时表现出 MFD，但在喂莫能菌素时没有表现出额外的 MFD，并且在莫能菌素停药后出现了乳脂反弹。第二对奶牛（M 反应型）在从 SFS 日粮切换到 RFS 日粮时没有表现出 MFD，但在喂莫能菌素时表现出强烈的 MFD，并且在莫能菌素停药后没有恢复。两组奶牛在饮食变化时都出现了 BCC 的主要变化，包括既改变又不改变乳脂生产的饮食变化。第三对奶牛（SM 反应型）在 RFS 和 RFS/Mon 日粮中都表现出乳脂减少，并且在莫能菌素停药后乳脂恢复到 RFS 日粮的水平；这些奶牛对淀粉来源和莫能菌素的反应都表现出 BCC 的更缓慢变化。第四对奶牛（无反应型）在饮食处理时没有表现出乳脂百分率的变化，并且在饮食处理时 BCC 只发生了微小的变化。无论乳脂反应如何，在莫能菌素停药后，BCC 都不会恢复到原来的状态，尽管在 M 反应型奶牛中这种差异最强。在大多数（但不是所有）MFD 易感（S-、M-或 SM-反应型）奶牛中，与乳脂非反应型奶牛相比，有一个扩增片段（代表单个细菌物种）的长度升高，而在 MFD 条件下，有两个扩增片段的丰度降低。总的来说，这项研究表明 MFD 与瘤胃微生物群落的整体变化有关。
