Quantitative lipidomic analysis of blood and milk in jennies with high and low milk fat content

• Composition of jenny blood lipids reflected mainly diet composition, but not milk fat content. • Jenny milk fat depends mainly on the synthesis by mammary tissue. • 1,2-distearoyl-sn-glycerol may be a potential marker for low milk fat content in jennies. • Difference in milk fat content lies mainly in triglycerides, especially C8-C18 fatty acids. Jenny milk is characterized by low fat content and individual variability. To test the association between blood and milk lipid profiles between jennies with high-fat (HF) and low-fat (LF) content in milk, we compared blood and milk lipid compositions between HF and LF jennies on the same feeding and management regimes. Milk fat yield and milk fat content were greater in the HF than LF group, but milk yield, lactose and protein contents, density, pH, and somatic cell count did not differ between groups. Milk fat content was correlated negatively with density and positively with pH and SCC. In blood, glycerophospholipids accounted for more than 50% of total lipids (TL), while glycerolipids accounted for more than 50% of TL in milk. The composition or concentration of TL and lipid subclasses in the blood did not differ between the HF and LF groups, with only 11 lipid species differing. In milk, the composition and concentration of TL, 17 lipid subclasses, and 131 lipid species differed between groups. The main upregulated lipid compounds were triglycerides which consisted of C16 and C18 fatty acids, while the downregulated compound was 1,2-distearoyl-sn-glycerol (DSG). These differential lipids were involved in 8 metabolic pathways, including cholesterol metabolism, vitamins digestion and absorption, GL metabolism, regulation of lipolysis in adipocytes, fat digestion and absorption, and thermogenesis. We concluded that: 1) blood lipidomic profile cannot be used to predict milk fat content and composition in jenny; 2) the synthesis of jenny milk fat is influenced primarily by mammary tissue.