Marden J P, Julien C, Monteils V, Auclair E, Moncoulon R, Bayourthe C
INRA, Université de Toulouse, INPT-ENSAT, UMR 1289 TANDEM, F-31326 Castanet-Tolosan, France.
J Dairy Sci. 2008 Sep;91(9):3528-35. doi: 10.3168/jds.2007-0889.
The objectives of this study were to evaluate the capacity of 2 dietary feed additives, sodium bicarbonate and live yeast Saccharomyces cerevisiae (strain Sc 47), in optimizing ruminal pH in dairy cows and to determine their modes of action. Three early lactating Holstein cows, fitted with ruminal cannulas, were allocated in a 3 x 3 Latin square design. They were given a total mixed ration as control diet (CD) at a daily feeding rate of 28.0 kg of dry matter (DM)/cow supplemented with 150 g/d of sodium bicarbonate (SBD) or 5 g/d of live yeast (YD) during a 21-d experimental period (14 d of diet adaptation, 4 consecutive days of measurement and sampling and 3 d of transition). The pH and redox potential (E(h)) were measured from 1 h before feeding to 8 h after feeding at 1-h intervals, and samples of ruminal fluid were taken at 0, 2, 4, 6, and 8 h after feeding for the determination of volatile fatty acids and lactate concentrations. Total tract apparent digestibility of the diet was also determined. Ruminal pH fluctuated between 6.53 at feeding and 5.57 at 5 h postfeeding. Mean pH was greater with SBD (6.21) and YD (6.14) compared with CD (5.94), showing that both additives had a pH stabilization effect. The E(h) varied from -88 mV at 1 h before feeding to -165 mV at 1 h after feeding. Mean E(h) and Clark's Exponent (rH) were lower with YD (-149 mV and 7.31, respectively) than with SBD (-137 mV and 7.85, respectively) and CD (-115 mV and 8.05, respectively), indicating that the yeast strengthened the reducing power of the milieu. Total volatile fatty acids were greater in SBD (95.3 mM) and YD (99.4 mM) compared with CD (85.3 mM). Acetate concentration was greater in SBD (60.8 mM) and YD (59.1 mM) compared with CD (53.2 mM). Propionate concentration was greater in YD (25.8 mM) than in SBD (20.0 mM) and CD (18.0 mM). Butyrate remained constant between diets. Mean total lactate concentrations were 16.5, 12.2, and 5.4 mM for CD, SBD, and YD, respectively, with a 67% decrease with YD. Total tract organic matter digestibility was greater for YD (66.6%) compared with SBD (61.7%) and CD (62.2%). The neutral detergent fiber digestibility was greater with YD (41.6%) compared with SBD (34.3%) and CD (29.6%), whereas acid detergent fiber digestibility was greatest in YD (32.3%), intermediate in SBD (24.4%), and lowest in CD (18.1%). By inducing a lower ruminal E(h) and rH, live yeast prevented accumulation of lactate and allowed better fiber digestion, whereas sodium bicarbonate seemed to act only as an exogenous buffer.
本研究的目的是评估两种日粮饲料添加剂（碳酸氢钠和活酵母酿酒酵母菌株Sc 47）优化奶牛瘤胃pH值的能力，并确定它们的作用方式。选用3头装有瘤胃瘘管的初产荷斯坦奶牛，采用3×3拉丁方设计。在21天的试验期内（14天日粮适应期、连续4天测量和采样以及3天过渡期），给奶牛饲喂全混合日粮作为对照日粮（CD），每日饲喂量为28.0千克干物质（DM）/头，并分别补充150克/天的碳酸氢钠（SBD）或5克/天的活酵母（YD）。在饲喂前1小时至饲喂后8小时，每隔1小时测量pH值和氧化还原电位（E(h)），并在饲喂后0、2、4、6和8小时采集瘤胃液样本，测定挥发性脂肪酸和乳酸浓度。同时还测定了日粮的全消化道表观消化率。瘤胃pH值在饲喂时为6.53，在饲喂后5小时为5.57之间波动。与对照日粮（5.94）相比，SBD组（6.21）和YD组（6.14）的平均pH值更高，表明两种添加剂都有稳定pH值的作用。E(h)值从饲喂前1小时的-88 mV变化到饲喂后1小时的-165 mV。与SBD组（分别为-137 mV和7.85）和对照日粮组（分别为-115 mV和8.05）相比，YD组的平均E(h)和克拉克指数（rH）更低（分别为-149 mV和7.31），表明酵母增强了环境的还原能力。与对照日粮组（85.3 mM）相比，SBD组（95.3 mM）和YD组（99.4 mM）的总挥发性脂肪酸含量更高。与对照日粮组（53.2 mM）相比，SBD组（60.8 mM）和YD组（59.1 mM）的乙酸盐浓度更高。YD组（25.8 mM）的丙酸盐浓度高于SBD组（20.0 mM）和对照日粮组（18.0 mM）。各日粮组之间丁酸盐含量保持恒定。对照日粮组、SBD组和YD组的平均总乳酸浓度分别为16.5、12.2和5.4 mM，YD组降低了67%。与SBD组（61.7%）和对照日粮组（62.2%）相比，YD组的全消化道有机物消化率更高（66.6%）。与SBD组（34.3%）和对照日粮组（29.6%）相比，YD组的中性洗涤纤维消化率更高（41.6%），而酸性洗涤纤维消化率在YD组最高（32.3%），在SBD组居中（24.4%），在对照日粮组最低（18.1%）。通过降低瘤胃E(h)和rH，活酵母可防止乳酸积累并使纤维消化更好，而碳酸氢钠似乎仅作为一种外源性缓冲剂起作用。
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