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Evaluation of choline metabolites in milk as potential biomarkers for choline absorption in the lactating dairy cow
Choline is an essential nutrient for growth and performance of production animals, and an established symptom of choline deficiency in periparturient cattle is fatty liver. Dietary choline is extensively degraded in the rumen, and although rumen-protected choline (RPC) has been found to reduce the extent of hepatic fat infiltration, no biomarkers have been established to assess the efficacy of RPC supplements in dairy cows. Secretion of total choline in milk could be a potential biomarker; however, choline is secreted in milk in many metabolic forms and some specific metabolites in milk may be more closely associated with choline absorption than total choline secretion. The objective of this study was to evaluate secretion of choline metabolites in milk as potential biomarkers of choline absorption. Five lactating Holstein cows (237±17 DIM) were used in a 5×5 Latin square design, with 5-d treatment periods and a 2-d interval between periods. Treatments were 1) control (0 g/d choline), 2) RPC - low dose (RPC-L), 3) RPC - high dose (RPC-H), 4) abomasal infusion (ABO) – low dose (ABO-L), 5) ABO - high dose (ABO-H). The low and high doses of RPC (Reashure, Balchem Corporation) and ABO each supplied 12.5 and 25 g choline/d, respectively. Milk samples from d5 were analyzed for acetylcholine (AC), betaine (Bet), free choline (Cho), glycerophosphocholine, lysophosphocholine, phosphatidylcholine, phosphocholine (PC) and sphingomyelin, using liquid chromatography-tandem mass spectrometry. Although total choline secretion in milk was not affected by ABO, Cho and Bet secretion increased (P < 0.01) in a dose dependent manner with ABO by 74% and 171%, respectively, with ABO-L and 146% and 278%, respectively, with ABO-H. The amounts of Cho and Bet secreted in milk increased from 0.54 to 0.94 and 1.33 g/d and from 0.14 to 0.38 and 0.53 g/d, respectively for the low and high doses. Increases in the yields of AC and PC were also observed (P = 0.04), although only with ABO-H. The other metabolites were not changed by ABO (P > 0.12), nor were any changes observed in secretion of individual choline metabolites with RPC. Multiple regression indicated the changes in milk PC and Bet secretion could be explained to a large degree by the ABO dose of choline (P = 0.01; R2= 0.72). The results of this study suggest that some choline metabolites may be more sensitive biomarkers than total choline for absorption of supplemental choline.
Keywords:
Cholne, bioavailability, dairy cow