Effect of rumen‐protected choline on fat digestibility and lymph metabolome in dairy cows

AbstractObjectives were to determine the effects of supplementing rumen‐protected choline (RPC) from an established source with low (L, 28.8%) or a prototype with less lipid coating protection and high (H, 60.0%) concentrations of choline chloride on digestibility of fat and supra‐mammary lymph metabolome in feed‐restricted cows. Pregnant, nonlactating Holstein cows (n = 33; 11/treatment) at mean (±standard deviation) 231 ± 4.7 days of gestation were blocked by body condition (4.23 ± 0.47) and assigned to receive 0 (CON) or 25.8 g/d of choline ion from L (L25.8) or H (H25.8). Cows were adapted to the diet and then fed‐restricted to 42% of the net energy of lactation required for maintenance and pregnancy for 9 days. Intake of metabolizable methionine was maintained at 19 g/d. On Day 9, cows were fed 450 g of saturated fatty acids (SFA), and feces and blood were sampled continuously for 24 h. Supra‐mammary lymph was sampled 6 h after feeding SFA and metabolome was characterized. Feeding RPC increased digestibility of fat (CON = 80.4 vs. RPC = 86.0 ± 1.9%) and reduced the concentration of haptoglobin in serum (CON = 174 vs. RPC = 77 ± 14 µg/ml) independent of source of RPC fed. Feeding RPC increased the concentrations of triacylglycerol in serum (CON = 15.1 vs. RPC = 17.8 ± 1.9 mg/dl) in feed‐restricted cows after feeding SFA, and the increment tended to be greater for cows fed H25.8 than L25.8. Supplementing RPC tended to increase the concentrations of triacylglycerol (CON = 11.4 vs. RPC = 15.8 ± 3.4 mg/dl) in supra‐mammary lymph. Feeding RPC increased the concentration of choline and affected the concentrations of analytes involved in metabolic pathways associated with amino acid metabolism and biosynthesis of phospholipids in lymph compared with CON. Feeding RPC, independent of source used, increased fat digestibility with some changes in lymph metabolome in cows under negative nutrient balance.