Effect of Camelina sativa seeds on rumen microbiota and fermentation in dairy sheep

This study investigated the effect of three levels of Camelina sativa seeds on ewes' diet on rumen microbiota using 16S rRNA gene amplicon sequencing and biochemical assays, focusing on rumen fermentation parameters and carbohydrates, proteins, and fats metabolism. Forty-eight dairy ewes were assigned to four homogeneous groups based on the inclusion level of C. sativa seeds in the diet (0, 28, 51.3, and 74.6 g/kg DM; Control, CS6, CS11, and CS16, respectively). Rumen digesta were collected on the 60th day of the trial using an esophageal tube. Rumen fluid was analyzed for volatile fatty acids (VFAs) concentration and rumen enzymatic activity. In addition, rumen microbiota was characterized in both fluid and solid fractions. The acetic and propionic acid concentrations were higher (P < 0.001) in CS11 compared with Control and CS6. Iso-butyric, butyric, iso-valeric, valeric acid, and total VFAs concentrations were higher (P < 0.05) in CS11 than in Control. The acetic: propionic ratio was higher (P = 0.003) in Control than in CS11 and CS16. Amylase activity was lower (P < 0.001) in CS6. In rumen fluid, CS11 and CS16 had a lower -biodiversity than the Control, while composition also differed (P ≤ 0.05). Regarding the most notable results of the taxa relative abundance, as compared with CS11 and CS16, Ruminobacter and Succinimonas relative abundances were lower (P < 0.05) in CS6, while Fibrobacter, Methanobrevibacter, Saccharofermentans, and Lachnospiraceae ND3007 group relative abundances were higher (P < 0.05). Ruminococcus was higher (P < 0.001) in CS6 than in Control. Fibrobacter was higher (P < 0.05) in the Control than in CS16. Butyrivibrio and Pseudobutyrivibrio were higher (P < 0.001) in CS11 compared with Control and CS6. Selenomonas -relative abundance was higher (P < 0.001) in CS16 than in Control and CS6. Higher inclusion levels were associated with reduced relative abundance of fibrolytic taxa and increased abundance of microbial groups linked to carbohydrate fermentation and -fatty acid biohydrogenation, with responses differing between rumen fluid and solid fractions. The lower-fat inclusion of C. sativa seeds could be associated with a relative enrichment of fibrolytic bacteria, potentially linked to greater phenolic bioavailabi-lity, whereas higher inclusion levels are associated with shifts toward amylolytic and propionate-associated taxa.