Dairy cattle products are often considered challenging for human health due to their composition measures, yet they provide beneficial nutrients to humans. This study evaluated the potential role of rumen microbes in modifying milk production and composition profile by subjecting four crossbred dairy cows to four different experimental diets over an 80-day period. The four diets were formulated to contain 10%, 20%, 30%, and 40% commercial dairy concentrate mixed with Rhodes grass (Chloris gayana) and Lucerne (Medicago sativa). Rumen liquor and milk samples were collected after every 20 days. Microbial composition and diversity were assessed using the v3-v4 regions of the 16S rRNA gene while the milk parameter composition was assayed using a Lactoscan. Statistical analysis was performed through ANOVA and Spearman correlation was used to assess the relationship between bacterial taxa communities and milk production and composition constituents. The results indicated that dietary modifications significantly affected rumen bacterial community composition. An increase in concentrate ratio across the diets led to an increase in the abundance of Bacteroidetes (P= 0.04) while that of Firmicutes and Fibrobacter numerically decreased. Bacteriodetes and Firmicutes were the dominant bacterial phyla making up to a total of 83.7% of the total rumen bacteria. On the other hand, a positive and significant correlation was exhibited between Prevotella (P= 0.036), Lentispaerae (P= 0.010), and Synergistetes (P= 0.011) with milk protein. The genus BF311 was also positively and significantly correlated with milk fat (P=0.03). Phylum Fusobacteria showed a negative correlation with milk lactose (P=0.016) as well as Tenericutes with milk protein (P= 0.009). These associations between the rumen microbiota and host phenotypes suggest that there might be some utilization relationship and productive association between dietary nutrients, affected bacterial groups, and milk production and composition.

Keywords: Rumen bacteria, diet, milk composition, milk production