| Popis: |
ABSTRACT: Choline feeding in the form of rumen-protected choline (RPC) has been shown to increase milk production and improve measures of metabolic health (e.g., liver triglyceride) in dairy cows. The objective was to characterize changes in plasma and milk choline and choline metabolite concentrations, including microbial-derived trimethylamine N-oxide (TMAO), in response to increasing ruminal spot-doses, different types of RPC, and ruminal stability of RPC in lactating cows. For experiment 1, 12 mid-lactation (121 ± 16.3 d in milk) Holstein cows were balanced by total plasma choline concentrations and milk yields. Cows were assigned to 1 of 3 lipid-encapsulated RPC products (main plots): prototypes P1, P2, and P3 (containing 59, 56, and 30% choline chloride, respectively). Within each main plot, cows were assigned to a sequence of doses in a 4 × 4 Latin square design: 0, 18, 36, or 54 g of choline chloride. Treatments were preconditioned with ground corn and administered as a single ruminal bolus once per experimental period 1 h postfeeding of a total mixed ration. For experiment 2, we compared a control (0 g of choline chloride) versus P2, and P4 and P5 (60 and 62% choline chloride, respectively) in a repeated 4 × 4 Latin square design. Experiment 2 followed a similar design as experiment 1 with modifications: 12 late-lactation (228 ± 7.10 d in milk) Holstein cows were used; treatments were administered as part of a premeal; and cows received a daily allowance of a total mixed ration as equal provisions every 4 h within 24 h before and after treatment. For both experiments, plasma and milk samples were collected for choline and choline metabolite quantification. Data were analyzed using a mixed model including fixed effects of treatment, period, and time. Contrast statements were used to test for linearity of dose and differences between prototypes for experiment 1 and 2, respectively. Plasma and milk TMAO concentrations increased with RPC dose (peak by h). Milk choline and betaine yields increased with RPC dose in a quadratic manner; albeit, dependent upon RPC type. Milk phosphocholine (PCho) and glycerophosphorylcholine (GPC) yields changed by select RPC dose (experiment 1), however Met, PCho, GPC, phosphatidylcholine, and total choline concentrations in milk, and plasma Met and sphingomyelin concentrations were not responsive. We conclude that plasma or milk choline, betaine, and TMAO concentrations are responsive to RPC type, dose, and stage of lactation evaluated. |
