Hepatic oxidation is responsive to prepartum energy and peripartum rumen protected choline supplementation

Controlling prepartum energy intake or supplementing rumen-protected choline (RPC) during the periparturient period, are two strategies to preserve hepatic metabolic function. The objective of this study was to examine the regulation of hepatic gluconeogesis and oxidation during the transition to lactation. At -48 days relative to calving (DRTC), multiparous Holstein cows were assigned to either a controlled (1.40 Mcal of NEL/kg DM; CE) or high (1.63 Mcal NEL/kg DM; HE) energy prepartum diet with or without RPC (top-dressed daily from -21 to +21 DRTC). Postpartum diets only differed by addition of RPC. Liver tissue biopsy samples were collected at -14, +7, +14, and +21 DRTC for RNA isolation and cDNA generation (n=16/treatment). Quantitative PCR was performed and mRNA abundance was normalized to reference genes. Data were analyzed by Proc Mixed (SAS 9.4) with repeated measures in a model that accounted for the main effects of RPC, energy, DRTC, and corresponding 2-way and 3-way interactions, and the random effect of cow(energy×choline). When interactions were significant (P<0.05), energy×choline means were separated by Tukey’s and time interactions were separated within timepoint by slice. Data are presented as least squares means + SE, arbitrary units (AU). Pyruvate carboxylase (PC) expression increased (P<0.05) after calving. There was an energy×choline (P<0.05) and choline×DRTC (P<0.05) interaction where RPC increased PC expression at -14 and +7 DRTC. There was no interaction (P>0.1) of prepartum energy and DRTC. Expression of cytosolic phosphoenolpyruvate carboxykinase (PEPCKc) was greatest (P<0.05) at +14 and lowest at -14 and +7 DRTC (1.62a, 0.75b, and 0.62b + 0.16 AU, respectively). Expression of PEPCKc was decreased (P<0.05) in cows fed HE+RPC compared with other treatments (0.57b, 1.00ab, 1.26a, 1.21a + 0.09 AU; HE+RPC, HE, CE+RPC, CE). Expression of glucose-6-phosphatase was increased (P<0.05) at +14 and +21 DRTC, and decreased (energy×choline; P<0.05) in cows fed the CE+RPC (1.36 vs. 2.32, 2.33, 2.24 + 0.17 AU; CE+RPC, CE, HE+RPC, HE). Expression of carnitine palmitoyltransferase 1A was greatest at +21 DRTC (P<0.05) but was unaltered (P>0.1) by energy or choline. The transcription factor PPARalpha was increased (P<0.05) in CE+RPC (1.35 vs. 0.86, 0.68, 0.90 + 0.08 AU; CE+RPC, CE, HE+RPC, HE). Increased PC peripartum with RPC, across energy treatments, may support increased oxidative capacity at calving. Decreased PEPCKc in HE+RPC may serve to increase oxidation of increased circulating NEFA by maintaining the oxaloacetate pool.