Quantitative differences in rumen epithelium proteins and detection of lysine acetylation in lambs fed a low or high metabolizable energy diet

Thirty-six Merino wethers (10-month-old) were fed ad libitum for 30 days two diets;1) low metabolizable energy diet (LME; 30% lucerne: 70% cereal chaff) and 2) high ME diet (HME; 40% rolled barley grain: 50% lucerne: 10% cereal chaff). Effects of diet on dry matter intake (DMI), metabolizable energy intake (MEI), liveweight (LWT), average daily gain (ADG), carcass lean or fat gain, liver and empty rumen weight and plasma metabolites were analysed. A membrane enriched protein fraction of rumen epithelium isolated enzymatically from whole depth rumen wall was quantified for each sheep using tandem mass tag mass spectrometry (TMT-MS). The presence or absence of acetylation of lysine residues on identified proteins was counted and the position of the lysine acetylation recorded. In lambs fed the HME diet, DMI (P<0.001), MEI (P<0.001), ADG (P<0.001), fat (P<0.001) and lean gain (P<0.001), as well as liver (P<0.001) and empty rumen (P<0.009) weight were greater than those fed the LME diet. Plasma glucose (P<0.001) and β hydroxybutyrate (P<0.001) at 3 and 5 h after feeding was greater in HME diet than in the LME fed lambs. Changes in rumen epithelium protein abundance in the LME versus HME fed lambs were associated with metabolism in the peroxisome, protein processing in the endoplasmic reticulum (ER), valine, leucine and isoleucine degradation and carbon metabolism. Acetylation of lysine was detected in enzymes involved in glycolysis, tricarboxylic acid (TCA) cycle and fatty acid (FA) metabolism. Quantitative differences in the abundance of rumen epithelium proteins that carry out intracellular processes of energy expenditure were associated with the concentration of ME (MJ/ kg DM) in the diet of growing lambs. The detection of lysine acetylation sites suggests a difference in the ME of the diet regulates enzymatic activity in central metabolic pathways in the rumen epithelium cells.