Abstract：
To investigate the effects of acetate, propionate, and pH on thermodynamics of volatile fatty acids (VFA) in the rumen, a dual-flow continuous culture study was conducted to quantify production of major VFA, interconversions among the VFA, and H2 and CH4 emissions in a 4 × 4 Latin square design. The 4 treatments were (1) control: pH buffered to an average of 6.75; (2) control plus 20 mmol/d of infused acetate (InfAc); (3) control plus 7 mmol/d of infused propionate (InfPr); and (4) a 0.5-unit decline in pH elicited by adjustment of the buffer (LowpH). All fermentors were fed 40 g of a pelleted diet containing whole alfalfa pellets and concentrate mix pellets (50:50) once daily. After 7 d of treatment, sequential, continuous infusions of [2-13C] sodium acetate (3.5 mmol/d), [U-13C] sodium propionate (2.9 mmol/d), and [1-13C] sodium butyrate (0.22 mmol/d) were carried out from 12 h before feeding for 36 h. Filtered liquid effluent (4 mL) was sampled at 0, 2, 4, 6, 8, 12, 16, and 22 h after feeding, and assessed for VFA concentrations, with another filtered sample (20 mL) used to quantify aqueous concentrations of CH4 and H2. Headspace CH4 and H2 gases were monitored continuously. Ruminal microbes were isolated from the mixed effluent samples, and the microbial community structure was analyzed using the 16S rRNA amplicon sequencing technique. The digestibility of neutral detergent fiber, acid detergent fiber, and starch and microbial C sequestrated from VFA were not affected by treatments. The LowpH treatment increased net propionate production and decreased H2 and CH4 headspace emissions, primarily due to shifts in metabolic pathways of VFA formation, likely due to the observed changes in bacterial community structure. Significant interconversions occurred between acetate and butyrate, whereas interconversions of other VFA with propionate were relatively small. The InfAc and InfPr treatments increased net acetate and propionate production, respectively; however, interconversions among VFA were not affected by pH, acetate, or propionate treatments, suggesting that thermodynamics might not be a primary influencer of metabolic pathways used for VFA formation.
摘要：
为了研究乙酸盐的作用，丙酸盐,和pH对瘤胃中挥发性脂肪酸（VFA）热力学的影响，进行了双流连续培养研究，以量化主要VFA的产量，VFA之间的相互转换，以及4×4拉丁方设计中的H2和CH4排放。4种处理是(1)对照:pH缓冲至平均6.75;(2)对照加20mmol/d输注的乙酸盐(InfAc);(3)对照加7mmol/d输注的丙酸盐(InfPr);和(4)通过调节缓冲液(LowpH)引起的0.5个单位的pH下降。所有发酵罐每天一次饲喂40g含有整个苜蓿颗粒和浓缩混合颗粒(50:50)的颗粒状饮食。治疗7d后，顺序，连续输注[2-13C]乙酸钠（3.5mmol/d），[U-13C]丙酸钠(2.9mmol/d),和[1-13C]丁酸钠(0.22mmol/d)从进料前12小时开始进行36小时。在进料后0、2、4、6、8、12、16和22小时对过滤后的液体流出物(4mL)取样，并评估VFA浓度，另一个过滤样品(20mL)用于定量CH4和H2的水溶液浓度。连续监测顶部空间CH4和H2气体。从混合废水样品中分离出瘤胃微生物，并使用16SrRNA扩增子测序技术分析了微生物群落结构。中性洗涤纤维的消化率，酸性洗涤剂纤维，从VFA中分离的淀粉和微生物C不受处理的影响。低pH处理增加了丙酸盐的净产量，并减少了H2和CH4的顶部空间排放，主要是由于VFA形成的代谢途径的变化，可能是由于观察到的细菌群落结构的变化。乙酸和丁酸之间发生显著的相互转化，而其他VFA与丙酸的相互转换相对较小。InfAc和InfPr处理增加了乙酸盐和丙酸盐的净产量，分别；然而，VFA之间的相互转化不受pH的影响，醋酸盐,或者丙酸治疗，这表明热力学可能不是VFA形成代谢途径的主要影响因素。
