Dietary marine algae and its influence on tissue gene network expression during milk fat depression in dairy ewes

Abstract

Supplementation of a linoleic acid-rich diet with marine algae reduces milk fat content while impacting milk fatty acid profile in dairy sheep. Unlike other ruminant species, in ovine there are limited data on the molecular mechanisms that may regulate adipose, liver, and mammary responses to dietary marine lipids. This study was conducted to investigate changes in mRNA expression and relative mRNA abundance of key enzymes involved in lipid metabolism in mammary, subcutaneous adipose and liver tissue in response to long-term milk fat depression induced by marine algae. Eleven Assaf ewes were randomly assigned to 2 experimental diets consisting of a TMR based on alfalfa hay and concentrate (40:60) supplemented with 25g of sunflower oil/kg DM plus 0 (SO; control diet) or 8g of marine algae/kg of DM (SOMA diet) for 54 d. Quantitative reverse transcription-PCR was used to study expression of target genes in tissues harvested at slaughter at the end of the feeding period (54 d). There was no effect of SOMA on mammary and adipose tissue expression of genes encoding proteins required for fatty acid uptake and activation (ACSS2, LPL), intracellular fatty acid transport (FABP3, FABP4), de novo fatty acid synthesis (ACACA, FASN), esterification (DGAT1, DGAT2, LPIN1), desaturation (SCD), elongation (ELOVL6), transcriptional regulation (INSIG1, MED1, PPARG, RXRA, SCAP, SREBF1, THRSP) and lipid droplet formation (ADFP, BTN1A1, XDH). Abundance of PPARG (0.04%) and INSIG1 (2.22%) in mammary tissue was markedly greater than that of SREBF1 (0.002%), suggesting that they may play a more important role in milk fat synthesis regulation. Addition of marine algae did not affect the expression of β-oxidation- and lipoprotein-related genes (ACOX1, APOB, CPT1A, PPARA, RXRA) in hepatic tissue. However, feeding SOMA up-regulated hepatic HMGCS2, which controls ketogenesis. Concentration of plasma β-hydroxybutyrate, NEFA, glucose, triacylglycerol, growth hormone, insulin-like growth factor 1, insulin, and leptin was not different between groups at d 54. Taken together with the milk fat responses and previous data from bovine fed similar diets, results suggest that transcriptional control mechanisms regulating fat synthesis in mammary secretory tissue were likely established during earlier stages of the feeding period.