Excessive Feed Sorting Is Associated With Altered Plasma Metabolism and Distinct Fermentation Responses of Pooled...

Feed sorting behaviour in dairy cows alters dietary structure and has been associated with rumen dysfunction, but its systemic metabolic consequences and microbial acidogenic potential remain unclear. This study combined in vivo and in vitro approaches to investigate associations between feed sorting behaviour, host metabolism, and rumen microbial fermentation. Twenty-four mid-lactation Holstein cows were monitored for 28 days, from which 12 cows representing extreme feed-sorting phenotypes were selected: severe sorters for fine particles (SES; n = 6) and slight sorters (SLS; n = 6). Blood samples were collected for biochemical and metabolomic analyses, and pooled rumen fluid from selected cows within each sorting category was incubated in vitro with high-concentrate or high-forage substrates. Excessive sorting cows exhibited higher alanine aminotransferase, total cholesterol, and low-density lipoprotein cholesterol concentrations. Metabolomic analysis revealed alterations in carbohydrate, lipid, and amino acid metabolism, including changes in D-mannose, fumaric acid, mevalonic acid, oleic acid, glutamic acid, tryptophan, and gamma-aminobutyric acid concentrations. These changes were accompanied by increased concentrations of PGE2, histamine, and arachidonoyl ethanolamide, consistent with altered inflammatory and endocannabinoid signalling. In vitro incubation of pooled SES- and SLS-derived inocula with high-concentrate and high-forage substrates generated distinct fermentation profiles. Treatments containing SES-derived inocula were characterised by lower pH and greater total volatile fatty acid concentrations, particularly under high-concentrate conditions. These fermentation patterns were associated with higher relative abundances of Succinivibrionaceae UCG-002, Lachnobacterium, and Pseudobutyrivibrio. Overall, these findings suggest that feed sorting behaviour is associated with alterations in systemic metabolism and rumen microbial fermentation characteristics, providing new insight into the relationship between feeding behaviour and metabolic health in dairy cows.