Temporal changes in plasma choline and choline metabolite concentrations in response to an esophageal bolus of rumen-protected fish oil in early lactation cows fed rumen-protected choline.

Fish oil (FO) is a rich source of docosahexaenoic acid (C22:6; DHA), which may be a preferable fatty acid (FA) for hepatic phosphatidylcholine (PC) synthesis via the actions of phosphatidylethanolamine N-methyltransferase. Our objective was to determine whether rumen- protected choline (RPC) feeding enhanced concentrations of circulating PC enriched with DHA in cows fed FO. Eighteen Holstein cows (3.6 ± 2 [mean ± SD] lactations) were randomly assigned to 2 groups (n = 9/ group) at −21 ± 3 d prepartum: unsupplemented (CON) or supplemented (CHOL) with RPC (0 or 60 g/d, respectively; 25% choline chloride; Ruprocol; Vetagro S.p.A., Reggio Emilia, Italy) until d 35 postpartum. At d 27 ± 4 postpartum, all cows were provided a gelatin capsule containing 100 g of lipid-encapsulated FO as an esophageal bolus (36% FO; 10.2 g of omega-3 FA; Prototype 6; Vetagro S.p.A.). Cows were fed a total mixed ration and milked twice daily. Blood was sampled at 0, 10, and 24 h, relative to bolus delivery. Plasma was analyzed for PC, lysoPC (LPC), choline, and choline metabolites using LC/MS. Data were analyzed under a mixed model with the random effect of cow, and the fixed effects of treatment, hour, and their interaction. At h 0, plasma betaine concentrations were greater in CHOL, relative to CON (P = 0.05); however, choline concentrations were not modified by treatment. FO increased circulating trimethylamine N-oxide and dimethylglycine (DMG) by h 10 (time, P < 0.03). DMG and methionine were greater in CHOL cows, relative to CON (P < 0.07). Although no changes were detected for plasma LPC-22:5 or −22:6, total LPC, or PC-16:0/22:5 or −18:0/22:5, RPC feeding increased plasma PC-16:0/22:6, −18:0/22:6, and LPC-20:5, compared with CON, following FO bolus (P < 0.07). Plasma PC-18:0/20:5 and total PC concentrations were greater in CHOL cows by h 24, relative to CON (treatment × time, P < 0.05). We conclude that RPC feeding augmented the ability of dietary FO to enhance PC synthesis in early lactation cows.