Several ruminal cellulolytic bacteria species are sensitive to pH and could therefore be used as biomarkers to determine the risk of sub-acute ruminal acidosis (SARA) in finishing lambs. This study compared a 2–4 h post feeding ruminal pH measurement to abundances of the ruminal pH-sensitive bacteria to evaluate the risk of SARA in a herd of 120 finishing lambs. The lambs were reared in individual units for 50 days. Ruminal fluid was collected by use of an orogastric tube on day 51 2-4 h after feeding. Although the lambs were fed an identical diet, they responded differently in the abundances of four ruminal pH sensitive cellulolytic bacteria (Ruminococcus albus, Ruminococcus flavefaciens and Fibrobacter succinogenes and Butyrivibrio fibrisolvens). Lambs with the most or the least cellulolytic bacteria were then classified as either lower SARA risk (LSR, n = 10) or higher SARA risk group (HSR, n = 10), respectively. Data showed that the ruminal pH and VFA profiles were uncorrelated with the number of cellulolytic bacteria (P > 0.050). Lambs with the HSR showed lower ruminal pH (P = 0.013) and acetate to propionate ratio (P = 0.018), higher concentrations of lactate (P = 0.035) and proportion of propionate (P = 0.033) compared to those with the LSR. The DMI and ADG did not differ in LSR and HSR lambs (P > 0.050). A diversity analysis revealed significantly lower diversity in HSR lambs than in LSR (Simpson index, P = 0.004). The relative abundances of the phyla Bacteroidetes, Fibrobacteres, Verruomicrobia, and Proteobacteria were higher in LSR lambs than in HSR (P < 0.050). The abundances of several phyla including Firmicutes, Tenericutes and Actinobacteria were higher in the HSR than in the LSR group (P < 0.050). The bacterial communities of the LSR and HSR clustered separately in rumen based on the Unifrac distances, indicating distinct bacteria communities at OTU level between the LSR and HSR lambs. Overall, there was no correlation between 2 and 4 h post-feeding ruminal pH and the abundance of pH-sensitive bacteria and the amount of these bacteria could be used as a potential biomarker of SARA in lamb herd.

Supplementation with saccharomyces cerevisiae culture products (SCs) has shown effectiveness in alleviating or improving the health and productivity of ruminants at a high risk of digestive and metabolic problems as a consequence of their physiological state and feeding system (i.e., Holstein cows during peak lactation). However, the effects of SC supplementation on ruminal digestion and microbial population are not yet well-understood. Hence, this study aimed to contribute to the knowledge of the effects of in vitro SC supplementation on ruminal nutrient digestibility and microbial community. This study included three treatment groups: a control group (CON, 0% SC proportion of substrate DM), a low-dose SC group (LSC, 0.10% SC proportion of substrate DM), and a high-dose SC group (HSC, 0.30% SC proportion of substrate DM). The SC product contained 7.0 × 109 CFU/g. After 48 h of fermentation at 39 °C, the incubation fluid and residue were collected to measure the ruminal nutrient digestibility and microbial community. The results showed that supplemental SC tended (p = 0.096) to increase DM digestibility due to an increase (9.6%, p = 0.03) in CP digestibility and via a tendency (0.05 < p < 0.08) to increase the fiber fraction. Additionally, the 16S rRNA high-throughput sequencing results revealed that the richness and diversity of the microbiota were unchanged by SC supplementation, while the abundances of Spirochaetes, Tenericutes, and Spirochaetaceae were lower in the SC groups than those in the CON group (p < 0.05). At the genus level, the abundances of Selenomonas and Succinivibrio were increased by SC supplementation (p < 0.05), while SC supplementation decreased the abundances of Ruminococcaceae_UCG-014 and Treponema_2 (p < 0.05). Furthermore, the predicted function of the microbiota showed that carbohydrate metabolism and lipid metabolism were enriched in the SC groups compared with the CON group (p < 0.05). Except for the increases in ADF digestibility (p = 0.032) and pH (p = 0.076) at 0.30%, the supplemental level did not result in additional effects. In summary, our results demonstrate that SC supplementation could improve ruminal nutrient degradation digestibility and alter microbiota composition.