title: Effect of dietary vitamin C on concentrations of ascorbic acid in plasma and milk.
abstract: The addition of exogenous ascorbic acid to milk reduces the development of oxidized flavor. This experiment was conducted to determine whether feeding ascorbic acid to cows influenced vitamin C concentrations in milk. Thirty-two midlactation Holstein cows were fed a basal diet of 56% forage, 36.6% concentrate, and 7.4% roasted whole soybeans (dry basis) that was top-dressed with a premix that provided 0, 3, 16.5, or 30 g/d of L-ascorbic acid (provided by ascorbyl-2-polyphosphate) for 28 d. Supplementation had no effect on milk yield or composition or dry matter intake. Treatment linearly increased plasma concentrations of ascorbic acid (19.8, 22.3, 21.9, and 25.7 mumol/L, respectively) but had no effect on plasma dehydro-L-ascorbic acid (DHAA). Concentrations of ascorbic acid (103.7 mumol/L) and DHAA (9.5 mumol/L) in milk were not affected by treatment. Secretion of ascorbic acid into milk appeared to follow Michaelis-Menton kinetics, with a Vmax of 3.92 mmol/d and a Km of 3.59 mumol/L. Milk flavor as evaluated by a panel was normal for all samples after 1 d of storage. After 7 d of storage, the average flavor score was 2.5 (moderate oxidized flavor), but no differences among treatments were observed. Supplemental dietary vitamin C did not increase vitamin C concentration in milk, probably because the maximum potential secretion of the vitamin was occurring in unsupplemented cows.
authors.affiliation: Department of Animal Sciences, Ohio Agricultural Research and Development Center, Ohio State University, Wooster 44691, USA. weiss.6@osu.edu
authors.forename: W P
authors.initials: WP
authors.lastname: Weiss
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000008:administration & dosage* / Q000032:analysis* / Q000097:blood / Q000493:pharmacokinetics; D002417:Cattle / Q000378:metabolism / Q000502:physiology*; D019587:Dietary Supplements; D004305:Dose-Response Relationship, Drug; D005260:Female; D008892:Milk / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D011897:Random Allocation; D013649:Taste
chemical_list: D001205:Ascorbic Acid