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.

This study describes the development of the rabbit caecum microbiota and its metabolic activities from the neonatal (day 2) until the subadult period

The objectives of this study were to characterize the establishment of ruminal fermentation and enzymatic activities in dairy calves from birth to weaning (d 83). Six Holstein calves, immediately separated from their mother at birth, were fed colostrum for 3 d after birth, and thereafter milk replacer, starter pelleted concentrate, and hay until d 83 of age. Ruminal samples were collected from each calf every day for the first 10 d, and additionally at d 12, 15, 19, 22, 26, 29, 33, 36, 40, 43, 47, 50, 55, 62, 69, and 83. Ruminal samples were collected 1h after milk feeding with a stomach tube. The pH and redox potential (E(h)) were immediately measured. Samples were kept for further determination of ammonia nitrogen (NH(3)-N) and volatile fatty acid (VFA) concentrations, and xylanase, amylase, urease, and protease activities. Ruminal pH averaged 6.69, 5.82, and 6.34, from d 1 to 9, d 10 to 40, and d 43 to 83 of age, respectively. At first day of life, the ruminal E(h) value was positive (+224 mV). From d 2 to 9, d 10 to 40, and d 43 to 83 of age, ruminal E(h) averaged -164, -115, and -141 mV, respectively. From d 1 to 3, d 4 to 22, and d 26 to 83 of age, NH(3)-N concentration averaged 60.1, 179.8, and 58.2 mg/L, respectively. No VFA were detected in ruminal samples collected on d 1 of life of calves. From d 2 to 10 and d 12 to 83 of age, ruminal total VFA concentration averaged 19.5 and 84.4mM, respectively. Neither ruminal xylanase or amylase activities were observed at d 1 of age. From d 5 to 15 and d 19 to 83 of age, the xylanase activity averaged 182.2 and 62.4 μmol of sugar released per hour per gram of ruminal content dry matter (DM), respectively. From d 5 to 83 of age, the amylase activity reached 35.4 μmol of sugar released per hour per gram of ruminal content DM. The ruminal ureolytic activity was observed with an average value of 6.9 μg of NH(3)-N released per minute per gram of ruminal content DM over the 83-d experimental period. From d 1 to 4 and d 5 to 83 of age, the proteolytic activity was 8.2 and 27.9 optical density units per hour per gram of ruminal content DM, respectively. The fermentative and enzymatic activities were rapidly established in the rumen from d 2 after birth. Most parameters did not evolve further after 1 mo of age.

A bacteria library was constructed from the caecum of a rabbit maintained under standard conditions. The complete gene 16S rRNA gene was sequenced. T