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Estimated postruminal bioavailability of rumen-protected lysine using plasma area under the curve methodology.

V. M. R. Malacco



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Estimated postruminal bioavailability of rumen-protected lysine using plasma area under the curve methodology.
V. M. R. Malacco*1,3, P. Doane2, R. B. Reis3, L. Beckett1, S. Hielger1, N. Briggs1, C. McCabe1, A. Torres1, S. S. Donkin1. 1Department of Animal Sciences, Purdue University West Lafayette, IN, 2Archer Daniels Midland Company Decatur, IL, 3Department of Animal Sciences, College of Veterinary Medicine, Federal University of Minas Gerais Belo Horizonte, MG, Brazil.

Products purported to provide rumen-protected Lys (RP-Lys) must be evaluated for postruminal delivery of Lys for absorption and metabolism. The objective of this study was to determine the relative bioavailability (BA) of intestinal absorption for RP-Lys using the plasma area under the curve (AUC) methodology. Three lactating rumen-cannulated Holstein dairy cows weighing 724 � 28 kg, producing 31.4 � 5.1 kg/d of milk were used in a 3 � 3 Latin square design. Each period consisted of 6 d of washout and 1 d of infusion and sampling. Cows were fed a basal TMR diet formulated to meet or exceed protein, Lys, and Met requirements. A PVC tube was temporarily inserted through the rumen cannula into the omasum and treatments (TRT) were infused through the tubing. The positive control was 58.9 g of crystalline HCl-Lys, assumed to be 100% absorbed, diluted in 300 mL of water. The same amount of Lys in a RP form was infused (150 g - 39.3% of Lys, � 0.9), and the sham control was an abomasal infusion of 360 mL of water. Lysine was measured in blood samples collected before and at 30, 60, 90, 120, 240, 360 and 480 min following the infusions. Plasma Lys absorption was estimated from the AUC with respect to time. Data were analyzed using the MIXED procedure of SAS with the fixed effects of TRT and period and random effects of cow within TRT. The relative BA for RP-Lys was determined as the ratio of the RP-Lys AUC over the free HCl-Lys AUC after subtracting the AUC value from the water infusion. Postruminal dosing with HCl-Lys resulted in a greater AUC when compared with RP-Lys and water (354.7, 135.5, and 71.2 � 16.95 nmol�min�mL−1 for HCl-Lys, RP-Lys and water, respectively). The relative BA of the RP-Lys product was 22.7%. There was a trend (P = 0.08) for greater Lys half-life in the plasma for RP-Lys relative to water infusion (546, 853, −886 � 424.1 min for HCl-Lys, RP-Lys and water, respectively). Plasma Lys clearance rate with HCl-Lys was 0.16 � 0.1% min−1 between infusions. The results indicated that the RP-Lys product was able to deliver Lys and be absorbed in the small intestine.

Keywords: rumen-protected lysine, plasma lysine, dairy cow.