Six plant sources of hydrolyzable tannins (HT) or HT and condensed tannins (CT; designated as HT1, HT2, HT3, HT + CT1, HT + CT2, and HT + CT3) were evaluated to determine their effects in vitro on CH(4) production and on ruminal archaeal and protozoa populations, and to assess potential differences in biological activities between sources containing HT only or HT and CT. Samples HT1, HT2, and HT3 contained only HT, whereas samples HT + CT1, HT + CT2, and HT + CT3 contained HT and CT. In experiment 1, in vitro incubations with samples containing HT or HT + CT resulted in a decrease in CH(4) production of 0.6 and 5.5%, respectively, compared with that produced by incubations containing the added tannin binder polyethylene glycol-6000. Tannin also suppressed the population of methanogenic archaea in all incubations except those with HT2, with an average decrease of 11.6% in HT incubations (15.8, 7.09, and 12.0 in HT1, HT2, and HT3) and 28.6% in incubations containing HT + CT (35.0, 40.1, and 10.8 in HT + CT1, HT + CT2, and HT + CT3) when compared with incubations containing added polyethylene glycol-6000. The mean decrease in protozoal counts was 12.3% in HT and 36.2% in HT + CT incubations. Tannins increased in vitro pH, reduced total VFA concentrations, increased propionate concentrations, and decreased concentrations of iso-acids. In experiment 2, when a basal diet was incubated with graded levels of HT + CT1, HT + CT2, and HT + CT3, the total gas and CH4 production and archaeal and protozoal populations decreased as the concentration of tannins increased. Our results confirm that tannins suppress methanogenesis by reducing methanogenic populations in the rumen either directly or by reducing the protozoal population, thereby reducing methanogens symbiotically associated with the protozoal population. In addition, tannin sources containing both HT and CT were more potent in suppressing methanogenesis than those containing only HT.

Probiotics/prebiotics have the ability to modulate the balance and activities of the gastrointestinal (GI) microbiota, and are, thus, considered beneficial to the host animal and have been used as functional foods. Numerous factors, such as dietary and management constraints, have been shown to markedly affect the structure and activities of gut microbial communities in livestock animals. Previous studies reported the potential of probiotics and prebiotics in animal nutrition; however, their efficacies often vary and are inconsistent, possibly, in part, because the dynamics of the GI community have not been taken into consideration. Under stressed conditions, direct-fed microbials may be used to reduce the risk or severity of scours caused by disruption of the normal intestinal environment. The observable benefits of prebiotics may also be minimal in generally healthy calves, in which the microbial community is relatively stable. However, probiotic yeast strains have been administered with the aim of improving rumen fermentation efficiency by modulating microbial fermentation pathways. This review mainly focused on the benefits of probiotics/prebiotics on the GI microbial ecosystem in ruminants, which is deeply involved in nutrition and health for the animal.

Aims:  To quantitatively analyse the faecal bacterial communities of Holstein calves and track their succession up to 12 weeks of age. Methods and Results:  Faecal samples obtained from four female Holstein calves were analysed by the RNA‐based, sequence‐specific rRNA cleavage method. Twelve scissor probes covering major rumen bacterial groups were used, detecting c. 60–90% of the total 16S rRNAs. At 1 week of age, 16S rRNAs from members of the Bacteroides‐Prevotella group (40·0% of the total 16S rRNAs), Faecalibacterium (21·7%), the Clostridium coccoides–Eubacterium rectale group (16·7%) and the Atopobium cluster (10·9%) were detected at high levels. Throughout the 12‐week period, rRNAs of the Bacteroides‐Prevotella and the Cl. coccoides‐Eu. rectale groups constituted the major fraction of microbiota (c. 50–70% of the total). The relative abundances of the Atopobium cluster, Faecalibacterium, and some probiotic bacteria (such as those of the genera Lactobacillus and Bifidobacterium) decreased as the animal aged. Instead, an uncultivated rumen bacterial group, as well as Ruminococcus flavefaciens and Fibrobacter emerged at the detectable levels (1–2%) in the faeces sampled at a postweaning age. In addition, certain bacterial groups that were not covered by the probe suite increased as the animals aged. Conclusions:  Young calves undergo dynamic changes in their intestinal bacterial community during the first 12 weeks of life. As young ruminants undergo metabolic and physiological development in their digestive tracts in the transition from a monogastric to a ruminant animal at an early age, the intestinal bacterial community may reflect such development. Significance and Impact of the Study:  The succession of the bacterial communities in the faeces of calves was quantitatively monitored in the present study for the first time. The approach used here was demonstrated to be a useful means for determining the populations of predominant faecal bacterial groups in a variety of calf experiments in response to diet, stress and disease.

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