Dietary sunflower oil modulates milk fatty acid composition without major changes in adipose and mammary tissue fatty acid profile or related gene mRNA abundance in sheep

Abstract

There are very few studies in ruminants characterizing mammary and adipose tissue (AT) expression of genes and gene networks for diets causing variations in milk fatty acid (FA) composition without altering milk fat secretion, and even less complementing this information with data on tissue FA profiles. This work was conducted in sheep in order to investigate the response of the mammary gland and the subcutaneous and perirenal AT, in terms of FA profile and mRNA abundance of genes involved in lipid metabolism, to a diet known to modify milk FA composition. Ten lactating Assaf ewes were randomly assigned to two treatments consisting of a total mixed ration based on alfalfa hay and a concentrate (60 : 40) supplemented with 0 (control diet) or 25 (SO diet) g of sunflower oil/kg of diet dry matter for 7 weeks. Milk composition, including FA profile, was analysed after 48 days on treatments. On day 49, the animals were euthanized and tissue samples were collected to analyse FA and mRNA abundance of 16 candidate genes. Feeding SO did not affect animal performance but modified milk FA composition. Major changes included decreases in the concentration of FA derived from de novo synthesis (e.g. 12:0, 14:0 and 16:0) and increases in that of long-chain FA (e.g. 18:0, c9-18:1, trans-18:1 isomers and c9,t11-CLA); however, they were not accompanied by significant variations in the mRNA abundance of the studied lipogenic genes (i.e. ACACA, FASN, LPL, CD36, FABP3, SCD1 and SCD5) and transcription factors (SREBF1 and PPARG), or in the constituent FA of mammary tissue. Regarding the FA composition of AT, the little influence of SO did not appear to be linked to changes in gene mRNA abundance (decreases of GPAM and SREBF1 in both tissues, and of PPARG in the subcutaneous depot). Similarly, the great variation between AT (higher contents of saturated FA and trans-18:1 isomers in the perirenal, and of cis-18:1, c9,t11-CLA and n-3 PUFA in the subcutaneous AT) could not be related to differences in gene mRNA abundance due to tissue site (higher LPL and CD36, and lower SREBF1 in perirenal than in subcutaneous AT). Overall, these results suggest a marginal contribution of gene expression to the nutritional regulation of lipid metabolism in these tissues, at least with the examined diets and after 7 weeks on treatments. It cannot be ruled out, however, that the response to SO is mediated by other genes or post-transcriptional mechanisms.

Effect of Diet Supplementation with Combinations of Soybean and Linseed Oils on Milk Production and Fatty Acid Profile in Lactating Dairy Ewes

“…It could be explained by a higher intake and mammary uptake of the oleic acid contained in the oils ( Table 2). The increases in milk concentration of C18:0 in SO100 and SO25 were consistent with results from [37] after feeding 167 g/sheep·day of sunflower oil in a high concentrate ration and also with the inclusion of 2.5% sunflower oil in a 60:40 F/C diet [38].…”

“…Taking the RA/VA ratio as an estimator, the average conversion rate in oil treatments was in the order of 48 (±3.2)% (Table 4) similar to the 50% value reported by [38] and greater than those informed (35% and 30%) by other authors Figure 3. Relationships between vaccenic (VA, trans-11 C18:1) and rumenic (RA, cis-9, trans-11 C18:2) acid contents in ewe's milk.…”

“…Feeding sunflower oil at 2.5% of the diet did not change milk production nor fat, protein, lactose and total solids yields [38].…”

“…The highest numerical value of RA was observed in the SO50-LO50 treatment (3.04 g/100g FA) and the lowest when the oils were supplied in pure form (Table 4). Baseline values for RA of 0.69 g/100g AG were reported in diets with 60 forage: 40 concentrate reaching values of 1.18 g/100g after the inclusion of 2.5 sunflower oil at 2.5% of total DM intake [38].…”

“…In cows or goats supplemented with sources of linoleic acid, the presence of this FA in milk does not generally exceed more than 1.5 percentage units over basal [45] with increases in sheep's or goat's milk between +0.5 and +1.8 g/100g FA at an increase-rate of 0.07% (±0.02) per gram of linoleic acid/kg of DM ingested [44]. g/100g FA) when supplementing with sunflower oil at 2.5% of total DM intake [38].…”