Temporal changes in ruminal microbiota composition and diversity in dairy cows supplemented with a lactobacilli-based DFM

Bronwyn E. Campbell¹Mohammad Mahmudul Hassan^2*Robert J Moore¹Tim Olchowy³Martin Soust⁴Rafat Al Jassim⁵John I Alawneh^2*

• ¹School of Science, RMIT University, Bundoora, Victoria 3068, Australia, Melbourne, Australia
• ²School of Veterinary Science, Faculty of Science, The University of Queensland, Gatton, Queensland, Australia
• ³Faculty of Veterinary Medicine, University of Calgary, Calgary, Alberta, Canada T3R 1J3, Alberta, Canada
• ⁴Terragen Biotech Pty Ltd, Coolum Beach, Queensland, Australia
• ⁵Queensland Alliance for Agriculture and Food Innovation, University of Queensland, St Lucia, Queensland, Australia

The current study examined the effects of lactobacilli-based direct-fed microbial (DFM) supplementation on the microbiota composition and diversity in ruminal fluid samples collected from dairy cows. Over 16 months (September 2021 through January 2023), the rumen bacterial and archaeal communities of fifty cows, supplemented with the DFM (DFM; n = 25) or serving as unsupplemented controls (CON; n = 25), were examined using 16S rRNA gene amplification and sequence analysis of DNA extracted from ruminal samples. Microbial diversity was assessed through alpha-and beta-diversity metrics (p<0.05). Linear discriminant analysis effect size analysis was performed to identify taxa driving the changes seen in the microbiota between experimental groups and temporally within each group (p<0.05). Bacillota and Bacteroidota were the major bacterial phyla, while Methanobacteriaceae was the predominant archaeal family. Bacterial genera such as Eubacterium_Q, Atopobium sp. UBA7741, and Sharpea were significantly (p<0.05) more abundant in the DFM group, while Bacillus_P_294101 and SFMI01 had higher abundance in the CON group. Multivariable analysis identified which ruminal and archaeal genera were significantly associated with age, average milk production, DIM, time and supplementation. The results also indicated significant temporal variations in ruminal microbial diversity, with specific taxa exhibiting different abundances between the DFM and CON groups. This study provides insights into how DFM feed additives can modulate the ruminal microbiota in dairy cows, revealing specific microbial shifts in response to supplementation.