Noftsger S M, St-Pierre N R, Karnati S K R, Firkins J L
Department of Animal Sciences, Ohio State University, Columbus 43210, USA.
J Dairy Sci. 2003 Aug;86(8):2629-36. doi: 10.3168/jds.S0022-0302(03)73858-2.
2-Hydroxy-4-(methylthio) butanoic acid (HMB) positively affects milk composition and yield, potentially through ruminal actions. Four continuous culture fermenters were used to determine the optimal concentration of HMB for digestibility of organic matter (OM), neutral detergent fiber (NDF), acid detergent fiber (ADF), and hemicellulose and synthesis of microbial N. A highly degradable mix of hay and grain was used as a basal diet to simulate a typical lactation diet. Three concentrations of HMB (0, 0.055, and 0.110%) and one concentration of dl-Met (0.097%) were infused into the fermenters according to a 4 x 4 Latin square design. Digesta samples were collected during the last 3 d of each of the four 10-d experimental periods. Digestibility of OM, hemicellulose, and NDF was largely insensitive to treatment. Digestibility of ADF showed a quadratic effect to supplementation of HMB, with 0.055% having lower digestibility than 0 or 0.110%. Total production of VFA was not influenced by HMB supplementation, but differences in concentration and production of individual VFA were seen. Isobutyrate increased linearly with increasing HMB supplementation. Propionate concentration decreased linearly with increased HMB supplementation, but propionate production showed a quadratic trend (P = 0.13). A higher concentration of acetate was detected for dl-Met compared with the highest HMB concentration. There were trends (P < 0.15) for dl-Met to decrease the production of isobutyrate and to lower the concentration of butyrate when compared with HMB. Microbial efficiency was not different among treatments. The proportion of bacterial N produced from NH3-N decreased linearly with increasing HMB, and bacteria receiving dl-Met synthesized more N from NH3-N than those receiving HMB. These data suggest that supplementation of HMB may have a sparing effect on branched chain volatile fatty acids because the fatty acids are not needed to provide carbon for synthesis of valine, isoleucine and leucine with ammonia. Comparisons of bacterial community structure in the fermenter effluent samples using PCR amplicons containing the ribosomal intergenic spacer region and its flanking partial 16S ribosomal RNA gene showed no distinct banding patterns, though treatments tended to group together. Both Met and HMB affect the rumen microbial population, but Met supplied as dl-Met does not act identically to that supplied as HMB.
2-羟基-4-（甲硫基）丁酸（HMB）可能通过瘤胃作用对牛奶成分和产量产生积极影响。使用四个连续培养发酵罐来确定HMB对有机物（OM）、中性洗涤纤维（NDF）、酸性洗涤纤维（ADF）和半纤维素消化率以及微生物氮合成的最佳浓度。使用一种高降解性的干草和谷物混合物作为基础日粮来模拟典型的泌乳日粮。根据4×4拉丁方设计，将三种浓度的HMB（0、0.055和0.110%）和一种浓度的dl-蛋氨酸（0.097%）注入发酵罐。在四个10天实验期的每个实验期的最后3天收集消化物样本。OM、半纤维素和NDF的消化率在很大程度上对处理不敏感。ADF的消化率对HMB添加量呈二次效应，0.055%的消化率低于0或0.110%。添加HMB对挥发性脂肪酸（VFA）的总产量没有影响，但单个VFA的浓度和产量存在差异。异丁酸随HMB添加量的增加呈线性增加。丙酸浓度随HMB添加量的增加呈线性下降，但丙酸产量呈二次趋势（P = 0.13）。与最高HMB浓度相比，dl-蛋氨酸组检测到更高浓度的乙酸盐。与HMB相比，dl-蛋氨酸有降低异丁酸产量和降低丁酸盐浓度的趋势（P < 0.15）。各处理间微生物效率无差异。由氨态氮产生的细菌氮比例随HMB增加呈线性下降，接受dl-蛋氨酸的细菌从氨态氮合成的氮比接受HMB的细菌更多。这些数据表明，添加HMB可能对支链挥发性脂肪酸有节约作用，因为这些脂肪酸不需要为用氨合成缬氨酸、异亮氨酸和亮氨酸提供碳源。使用包含核糖体基因间隔区及其侧翼部分16S核糖体RNA基因的PCR扩增子对发酵罐流出物样本中的细菌群落结构进行比较，尽管处理组倾向于聚集在一起，但未显示出明显的条带模式。蛋氨酸和HMB均影响瘤胃微生物种群，但以dl-蛋氨酸形式供应的蛋氨酸与以HMB形式供应的蛋氨酸作用不同。
