Association of plasma insulin concentration to fatty acid distribution between milk fat and membrane synthesis

Abstract

We examined the association between plasma insulin concentration and fatty acid distribution to milk fat and membrane fractions (triglyceride and phospholipid, respectively) in dairy cows. Thirty-seven Holstein cows at 60 to 70 d postpartum were synchronized by 2 PGF(2α) injections 14 d apart. Plasma samples were taken before morning and evening milkings and milk samples were obtained at morning milking. Plasma insulin concentrations were determined and cows were retrospectively assigned to low insulin (LI; 2.8±0.2 ng/mL, n=6) or high insulin (HI; 5.9±0.6 ng/mL, n=7) experimental groups. Fatty acid analysis of milk samples demonstrated a possible association between plasma insulin concentration and the fatty acid composition in phospholipid and triglyceride fractions. In the HI group, monounsaturated fatty acid concentration tended to be higher in the triglyceride (Tg) fraction than the phospholipids (Pl) fraction. In the LI group, the concentrations of short- and medium-chain saturated fatty acids (<16 carbon chain length), considered de novo-synthesized fatty acids, were higher in the triglyceride fraction than the phospholipid fraction. These results imply that the primary source of saturated fatty acids for phospholipid synthesis, in both HI and LI groups, is the circulation, as reflected by a higher concentration of longer saturated fatty acids (>16 carbon chain length) in the phospholipid fraction. Finally, the phospholipid-to-triglyceride ratio was higher in the HI group than in the LI group. Together, the results indicate that fatty acid distribution between phospholipid (membrane) and triglyceride (fat) synthesis by the mammary gland is associated with fatty acid length, degree of unsaturation, and origin, and might be subject to metabolic hormone regulation. Furthermore, a lower triglyceride-to-phospholipid ratio in the HI group implies that high plasma insulin and low milk fat concentrations are associated with a shift in the size distribution of milk fat globules.

Altered concentrate to forage ratio in cows ration enhanced bioproduction of specific size subpopulation of milk fat globules

“…However, an association has been found between the composition of some milk constituents and mean diameter of the MFG. For example, MFG size is closely associated with its membrane's PL (Argov et al, 2008;Lopez, Medac, & Jimenez-Flores, 2010;Mesilati-Stahy & Argov-Argaman, 2014;Mesilati-Stahy et al, 2011) and fatty acid composition (Briard, Leconte, Michel, & Michalski, 2003;Couvreur, Hurtaud, Marnet, Faverdin, & Peyraud, 2007;Lopez et al, 2008;Mesilati-Stahy, Malka, & Argov-Argaman, 2012;Mesilati-Stahy et al, 2011;Michalski et al, 2006;O'Mahony, Auty, & McSweeney, 2005). Several studies have reported a positive correlation between MFG mean diameter and milk total lipid content (Couvreur et al, 2007;Menard et al, 2010) or with diurnal fat yield (Wiking, Stagsted, Bjorck, & Nielsen, 2004), while others found no positive correlation between fat content and MFG size (King, 1957;Walstra, 1969).…”

Milk Fat Content and DGAT1 Genotype Determine Lipid Composition of the Milk Fat Globule Membrane

“…Total lipids were extracted from 0.5 mL milk with 10 mL chloroform-methanol (2∶1, vol/vol) as described previously [21]. For the HPLC analysis, 100 µL chloroform–ethanol (97∶3 vol/vol) was added to the evaporated tubes containing lipids and stored at -20°C until injection into the HPLC.…”

“…In addition, a strong association between milk fat content and MFG size has been demonstrated in dairy cows [18], by diet-induced alterations in milk fat content [13], and by interspecies comparison of milk fat concentrations [19]. Milk fat content has also been associated with the composition of PL in MFG of dairy goats and cows [20], [21]. Furthermore, association between TAG and PL composition [12], [13], [14], [22] and MFG size has been illustrated in human as well as bovine milk.…”

Elevated concentrate-to-forage ratio in dairy cow rations is associated with a shift in the diameter of milk fat globules and remodeling of their membranes

“…Other parameters that have been shown to modulate milk fat content and MFG size are lactation stage (Mesilati-Stahy and Argov-Argaman, 2014) and genetic disposition (Couvreur et al, 2007;Argov-Argaman et al, 2013). Interestingly, conditions that induce changes in MFG mean diameter also change milk PL content and composition (Lopez et al, 2008;Mesilati-Stahy et al, 2012), suggesting a link between the metabolic pathways regulating the composition of the mammary gland cell membranes and MFG size. The effect of altered composition of MFGM on MFG size is still unclear, although in other cell models, regulation of intracellular lipid droplet size through altered membrane composition has been demonstrated (reviewed by Thiam et al, 2013).…”

“…Extraction of Total Lipids from Milk and Plasma. Total lipids were extracted from the milk using a protocol adapted from the cold-extraction procedure developed by Folch et al (1957), as previously described (Mesilati-Stahy et al, 2012). Briefly, each sample was extracted twice, once for lipid analysis by normal-phase LC and once for FA analysis by GC.…”