The mechanism underlying the shift in milk-fat-globule (MFG) mean diameter upon changing the concentrate-to-forage ratio in dairy cow rations was investigated. Cows were fed high-concentrate low-forage (HCLF) or high-forage low-concentrate (LCHF) rations for 4 weeks. Mean diameter of MFG, determined in raw whole milk, was 0.4 μm larger in the LCHF-fed vs. HCLF-fed group. The main compositional differences between treatments were found in a specific MFG subgroup with the diameter of 3.3 μm (F1), with higher capric, lauric, myristic and lower oleic acid concentrations in HCLF vs. LCHF milk. Similarly, lipid concentration differences between treatments were only found in F1, with higher triglyceride and phosphatidylethanolamine, and lower sphingomyelin concentrations in LCHF vs. HCLF milk. The higher MFG mean diameter in whole raw LCHF milk might therefore be attributed to increased secretion of F1-group MFG, while fat content and composition in the other MFG size groups remains unchanged.
