Abstract
BACKGROUND: Mastitis is known to alter milk lipid yield, but its effects on lipid composition in blood and milk remain less understood. This study investigated changes in fatty acid (FA) composition in blood lipid fractions and milk of dairy cows following an intramammary lipopolysaccharide (LPS) challenge and explored potential links associated with these changes. We hypothesized that intramammary LPS infusion would alter the FA composition of blood lipid fractions, and that milk FA composition would reflect these changes. Furthermore, we hypothesized that prostaglandin E(2) (PGE(2)) would be associated with changes in both blood and milk FA composition, functioning as a potential mediator of these changes. RESULTS: Ten lactating cows were split into two groups. The treatment group received intramammary infusions of 50 μg Escherichia coli LPS in both quarters of one udder half to induce clinical mastitis, and saline infusions in the quarters of the opposite udder half; the control group received saline infusions in one udder half only. Blood and foremilk were collected from individual cows or glands at -1, 3, 6, 12, and 24 h post-infusion. Blood lipids were fractionated into cholesterol esters, free fatty acids (FFA), phospholipids (PL), and triacylglycerides (TAG). The FA composition was analyzed via gas-liquid chromatography. Total plasma TAG, FFA, and PGE(2) concentrations were measured by colorimetric assay or ELISA. Statistical significance was determined using mixed models with Tukey's test. Lipopolysaccharide infusion did not affect total plasma TAG and FFA concentrations but increased plasma PGE(2) concentrations and Δ9 desaturation indices in plasma TAG. A distinct shift in FA composition in plasma phospholipids and TAG was observed between the treatment and control groups at 6 and 12 h post-infusion. Specifically, LPS increased the proportion of n-6 polyunsaturated FA (18:2, 18:3, 20:3, 20:4, 20:5) and FA with less than 16 carbons while decreasing the saturated FA (18:0 and 20:0) in plasma TAG at 6 and 12 h. However, the milk FA composition remained unchanged. CONCLUSION: Our findings indicate that transient intramammary LPS challenge influences systemic lipid metabolism without altering the milk FA composition, suggesting that mammary inflammatory responses affect blood lipids independently of milk lipid secretion.