Bioavailability of Rumen Protected Choline Sources When Supplemented at Different Concentrations

Abstract Text: Plasma choline is not an accurate measure of choline supplementation because of extensive liver metabolism. Our objective was to evaluate a method to estimate the bioavailability of rumen protected choline (RPC) products by comparing the response of plasma metabolites involved with choline metabolism. Choline chloride (0, 3, 6, or 9 g/d) was mixed in 2 L of isotonic solution and infused daily into the duodenum of 4 duodenally and ileal cannulated steers (337 ± 23.7 kg BW) in order to determine a response curve. An additional 6 steers and 2 heifers (322 ± 23.7 kg BW) were used in a replicated 4 × 4 Latin square experiment with 7 day periods in order to evaluate the RPC products. Both experiments were run concurrently and plasma was collected from all animals for 1 week prior to the start of the experiment. Choline chloride was provided using 2 rumen protection technologies (SF and BT; Kemin Industries, Inc.). Treatments provided the following daily amounts of choline chloride: 1) 13 grams by SF (LSF), 2) 36.0 grams by SF (HSF), 3) 14.5 grams by BT (LBT), and 4) 39.0 grams by BT (HBT). All treatments were mixed with 0.45 kg of a concentrate mix and individually fed. In both experiments, plasma was collected at 0, 4, and 8 hours after feeding on the last day of the baseline and each period. Plasma was analyzed for choline and amino acids. Response curves were determined by regressing plasma choline, methionine, homocysteine, and cysteine against infused dose using the Fit Model procedure in JMP^® (SAS Institute, 2010). These curves were used to calculate choline chloride delivered by RPC treatments. Plasma and calculated delivered choline chloride were analyzed using the Fit Model procedure in JMP^® with hour of sampling and treatment as fixed effects and cow as random effect. Plasma amino acids and choline did not differ (P > 0.05) between RPC treatments. Calculated delivered choline chloride (4.71, 3.81, 3.37, and 6.25 g/d) did not differ (P > 0.05) for the LSF, HSF, LBT, and HBT treatments, respectively. However, the calculated delivered choline chloride for the RPC products was greater (P < 0.05) than during the baseline period. This would suggest that the method was appropriate and both of the RPC products were effective in providing a source of choline chloride.

Keywords: rumen protection, choline chloride, bioavailability