Feeding rumen-protected choline to prepartum Holstein cows in negative energy balance increases circulating lipoprotein phosphatidylcholine and triglyceride concentrations

Rumen-protected choline (RPC) supplementation in dairy cows may increase hepatic phosphatidylcholine (PC) synthesis, thereby promoting triacylglycerol (TAG) secretion within very-low-density lipoproteins. To investigate the effects of dietary RPC on lipoprotein PC and TAG concentrations, pregnant, nonlactating, multiparous Holstein cows were supplemented with RPC (ReaShure, Balchem Corp.) at 0 (control), 30, 60, 90, and 120 g/d, corresponding to choline ion equivalents of 0, 6.45, 12.9, 19.4, and 25.0 g/d, respectively. Cows were fed diets that met or slightly exceeded their net energy and MP requirements for maintenance and pregnancy for 5 d, followed by a 9-d period of restricted intake (∼31% of these requirements). Preprandial plasma (n = 41, from cows in 0, 60, and 120 g/d RPC treatments) and liver samples (n = 72, from cows across all RPC treatments) were collected on d 9 of feed restriction. Plasma TAG-rich and low-density lipoprotein (LDL) fractions were isolated using liquid chromatography. Total TAG, cholesterol, and phospholipid concentrations in these lipoprotein fractions were measured. Circulating lipoprotein fractions and liver samples were processed for lipidomics. Data were analyzed using a mixed model, with calf birth weight and days prepartum at enrollment as covariates. Normalized omics data were natural-log-transformed. Plasma concentrations of total TAG within the TAG-rich lipoprotein fraction increased both linearly and quadratically, whereas total cholesterol exhibited a linear increase with higher RPC intake. In the LDL fraction, total TAG concentrations showed a similar linear and quadratic response, whereas total phospholipid concentrations increased linearly, and cholesterol concentrations remained unaffected by RPC supplementation. Most detectable PC and ether-linked PC species concentrations within the TAG-rich lipoprotein fraction increased linearly with RPC intake (42 out of 45 species; e.g., PC 34:3). Conversely, dietary RPC supplementation resulted in a modest increase in hepatic concentrations of PC species compared with the control (36 out of 57 species), characterized by an increase in highly unsaturated species (e.g., 36:5) and a decrease in those with a lower degree of saturation. Furthermore, increasing amounts of supplemental RPC resulted to linear, quadratic, and overall increases in the hepatic ratio of select PC to PE ion intensities compared with the control (8, 11, and 13 out of 17, respectively). In conclusion, RPC supplementation increased TAG concentrations within lipoprotein fractions in Holstein cows experiencing negative energy balance. The observed changes in hepatic and lipoprotein PC concentrations support enhanced very-low-density lipoprotein secretion in cows fed RPC. These findings suggest that RPC increases lipoprotein PC and TAG concentrations and reduces hepatic TAG deposition in dairy cows.