Size, numberand phospholipid composition of milk fat globules are affected by dietary conjugated linoleic acid.

Abstract

Milk fat globules (MFGs) surround the triacylglycerol core that composes milk fat. The aim of this study isto induce milk fat depression via dietary conjugated linoleic acid (CLA) supplementation to study MFG size parameters, numberand glycerophospholipid composition. Eighteen Holstein dairy cows (136 ± 28 days in milk, 571 ± 37.9 kg body weight, 27.6 ± 2.1 kg milk/day) were selected and randomly assigned to a control or CLA group for a 14-dayperiod. Cows were fed a basal diet (control, n = 8) or the control plus 400 g/day CLA (C18:2 cis-9, trans-11 38.1% and C18:2 trans-10, cis-12 36.8%) (n = 10) for 7 days after which the CLA group was switched to the basal diet for another 7 days along with the control group. Cow performance, milk composition, MFG size and numbers were measured daily. On the seventh day after the start of the experiment, milk samples were identified and the quantification of glycerophospholipid compounds, and RNA were isolated from milk fat samples for a real-time polymerase chain reaction. Compared with control, at Day 7 from the start of feeding, supplemental CLA did not affect milk production (28.09vs. 28.50 kg/day), dry matter intake (14.9vs. 15.4 kg/day), or milk protein (3.55/100vs. 3.70 g/100 ml) and lactose contents (5.11/100vs. 5.17 g/100 ml). However, although the specific surface area of MFG (2138vs. 1815 m²/kg) was greater, CLA reduced milk fat content (1.95/100vs 3.64 g/100 ml on Day 7) and particle size parameters of MFG. The number of MFG gradually decreased until Day 7 of feeding, and then increased by Day 14 (2.96 × 109 on Day 1, 1.63 × 109 on Day 7 and 2.28 × 109 on Day 14) in the CLA group. Compared with control, glycerophospholipid analysis revealed that concentrations of phosphatidylcholine (PC) (e.g., PC [16:0/18:1] 20322vs. 29793 nmol/L), lysophosphatidylethanolamine (LPE) (e.g., LPE [18:1] 956vs. 4610 nmol/L)and phosphatidylethanolamine (PE) (e.g., PE [16:0/18:1] 7000 vs. 9769 nmol/L) in milk lipids decreased during CLA feeding. In contrast, concentrations of phosphatidylinositol (PI) (e.g., PI [18:0/18:1] 4052vs. 1799 nmol/L) and phosphatidylserine (PS) (e.g., PS [18:1/18:2] 9500 vs. 6843 nmol/L) increased. The messenger RNA abundance of fatty acid synthase, diacylglycerol O-acyltransferase 1, glycerol-3-phosphate acyltransferase 4and phosphate cytidylyltransferase 1, choline, alpha (PCYT1A) were downregulated in the CLA group, confirming published data demonstrating a negative effect of CLA on lipogenesis in the mammary gland. Overall, these results provided evidence for the important role of lipogenic gene expression in the regulation of MFG size, number and glycerophospholipid composition.