Effects of Key Rumen Bacteria and Metabolites on the Milk Fatty Acid Pro file in Dairy Cattle

This study was conducted in the animal field at the Faculty of Agriculture  University of Basra, with the aim of evaluating the relationship between  microbial diversity in cow rumens and fatty acid profiles in milk, with a  focus on the role of new biosynthesis (De Novo Lipogenesis (DNL) in the  mammary gland. Twenty dairy cows were used in similar age and production,  and were fed a forage of 60% roughage material and 40% concentrated with  a neutral fiber (NDF) ratio of about 42% dry matter. Rumen components  were analyzed in terms of pH, NH₃–N, and volatile fatty acids (VFA), in  addition to estimating microbial diversity using 16S rRNA gene sequencing,  and fatty acid profile analysis in milk using GC–FID. The results showed that  a balanced food environment led to high microbial diversity (Shannon = 3.6  ± 0.15, Simpson = 0.88 ± 0.02) with the predominance of cellulolytic species  Ruminococcus albus and Fibrobacter succinogenes, followed by Prevotella  ruminicola and Butyrivibrio fibrisolvens. This microbial balance contributed  to an increase in the production of acetate (65%) and butyrate (11%), the  two main pillars of the DNL process, which was reflected in the high content  of short and medium-chain saturated fatty acids (C14:0, C16:0) in milk.  A positive association was also found between microflora diversity and a  higher proportion of beneficial unsaturated acids such as oleic acid (C18:1  cis-9) and conjugated linoleic acid (CLA; C18:2 C9, T11) as a result of the  activity of partially hydrogenated bacteria. These findings are an important  step towards developing microbiome-based precision feeding strategies to  improve milk productivity and quality in domestic cows.