Submitted to: Journal Dairy Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 4/23/2010
Publication Date: 7/12/2010
Citation: Broderick, G.A., Reynal, S., Patton, R.A., Heimbeck, W., Lodi, P. 2010. Use of plasma concentrations to estimate bioavailability of methionine in rumen-protected products fed to dairy cows. Journal of Dairy Science. 93(E-Supplement 1):236. Interpretive Summary:
Technical Abstract: Plasma AA level was used to estimate Met bioavailability in 2 sources of rumen-protected Met (RPM): Mepron (RPM1) and Smartamine M (RPM2). Eight cows, consuming 22 kg DM/d, yielding 34 kg milk/d and fitted with ruminal cannulae, were fed a basal TMR containing (DM basis) 14% alfalfa silage, 54% corn silage, 7% grass hay, 9% ground shelled corn, 13% soybean meal, 3% additives, 15.7% CP, and 36% NDF. The TMR were fed at 6-hour intervals in 4 equal portions each day. For the calibration phase, cows were blocked by DIM into 2 squares and randomly assigned to balanced 4x4 Latin squares with 3-d periods. Solutions of DL-Met were infused into the abomasa via tubes inserted through the ruminal cannulae and omasal orifice to provide 0, 8, 16, and 24 g Met/d. Amounts actually infused were measured daily. Blood samples were collected from alternate jugular veins every h over the last 6 h of the 3-d period. Blood plasma was deproteinized and stored at –20°C until analyzed. For the feeding phase, cows were re-randomized within square and assigned to 4 treatments: 0, 24 g Met/d fed as 28.2 g/d of RPM1 or 31.6 g/d of RPM2, or 24 g DL-Met infused into the abomasum. Both RPM1 and RPM2 were fed 4 times daily by hand-mixing 1/4 the daily dose into the TMR. Design and blood sampling were the same as the calibration phase except periods were 7-d; abomasal Met infusion was for the last 72 h of each period. Plasma Met concentration was determined by ion-exchange chromatography with ninhydrin detection. Plasma Met was regressed on Met infusion levels using Proc GLM in SAS to develop the response curve to estimate Met bioavailability after correction for recovery of DL-Met infused during the feeding phase. The regression equation from the calibration phase was: Plasma Met (µM) = 0.498*Met infused (g/d) + 3.42 µM (P < 0.0001; r2 = 0.533). Rearranging and applying this equation yielded a mean recovery of infused Met of 95%. Mean (±SE) bioavailabilities, corrected to 100% recovery of infused Met, were 75 (±20)% for RPM1 and 88 (±23)% for RPM2. These bioavailabilities were not different (P = 0.51) within the precision of this study.