Molecular signatures of longissimus dorsi differ between dairy cattle based on prepartum muscle reserves and branched-chain volatile fatty acid supplementation.

Dairy cattle with high (HM) versus low muscle (LM) reserves exhibit distinct temporal changes in longissimus dorsi muscle depth (LDD) in late gestation. Branched-chain volatile fatty acids (BCVFA) supplementation increased blood glucose levels. We hypothesized that differences in HM and LM reflect distinct muscle metabolism and BCVFA supplementation altered metabolic pathways. At 42 d before expected calving (BEC) Holstein dairy cows were enrolled in a 2 x 2 factorial study of diet and muscle reserves, by assigning to control (CON) or BCVFA supplemented diets and LDD of HM (>4.6 cm) or LM (≤4.6 cm) groups: HM-CON (n=13), HM-BCVFA (n=10), LM-CON (n=9), and LM-BCVFA (n=9). Longisumus dorsi was biopsied at 21 d BEC, total RNA isolated and protein coding gene expression measured with RNA-seq. Between HM and LM 713 genes were differentially expressed and 481 between BCVFA and CON (P<0.05). Transcriptional signatures indicated differential distribution of Type II fibers between groups, with MYH1 greater in LM and MYH2 greater in HM cattle (P<0.05). Signatures of LM cattle relative to HM indicated greater activation of autophagy, ubiquitin-proteasome, and Ca2+-calpain pathways. HM cattle displayed greater expression of genes that encode extracellular matrix proteins and factors that regulate their proteolysis and turnover. BCVFA modified transcriptomes by increasing expression of genes that regulate fatty acid degradation and flux of carbons into the TCA cycle as acetyl CoA. Molecular signatures support distinct metabolic strategies between LM and HM cattle, and that BCVFA supplementation increased substrates for energy generation.

Long Chain Fatty Acids Mediate Hepatic Metabolic Flux in Preruminating Dairy Calves Fed Flaxseed Oil, High Oleic Soybean Oil, or Milk Fat.

Nutrition and physiological state affect hepatic metabolism. Our objective was to determine if feeding flaxseed oil (∼50% C18:3n-3 cis), high oleic soybean oil (∼70% C18:1 cis-9), or milk fat (∼50% C16:0) alters hepatic expression of PC, PCK1, and PCK2 and the flow of carbons from propionate and pyruvate into the TCA cycle in preruminating calves. Male Holstein calves (n = 40) were assigned to a diet of skim milk with either: 3% milk fat (MF; n = 8), 3% flaxseed oil (Flax; n = 8), 3% high oleic soybean oil (HOSO; n = 8), 1.5% MF + 1.5% high oleic soybean oil (MF-HOSO; n = 8), or 1.5% MF + 1.5% flaxseed oil (MF-Flax; n = 8) from d 14 to d 21 postnatal. At d 21 postnatal, a liver biopsy was taken for gene expression and metabolic flux analysis. Liver explants were incubated in [U-13C] propionate and [U-13C] pyruvate to trace carbon flux through TCA cycle intermediates or with [U-14C] lactate, [1-14C] palmitic acid, or [2-14C] propionate to quantify substrate oxidation to CO2 and acid soluble products. Compared with other treatments, plasma C18:3n-3 cis was 10 times higher and C18:1 cis-9 was 3 times lower in both flax (Flax and MF-Flax) treatments. PC, PCK1, and PCK2 expression and flux of [U-13C] pyruvate as well as [U-13C] propionate were not different between treatments. PC expression was negatively correlated with the enrichment of citrate M+5 and malate M+3, and PCK2 was negatively correlated with citrate M+5, suggesting that when expression of these enzymes is increased, carbon from pyruvate enters the TCA cycle via PC mediated carboxylation, and then OAA is converted to phosphoenolpyruvate via PCK2. Acid soluble product formation and PC expression were reduced in HOSO (MF-HOSO and HOSO) treatments compared with flax (MF-Flax and Flax), indicating that fatty acids regulate PC expression and carbon flux, but that fatty acid flux control points are not connected to PC, PCK1, or PCK2. In conclusion, fatty acids regulate hepatic expression of PC, PCK1, and PCK2, and carbon flux, but the point of control is distinct.