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Using plasma sulfur amino acid concentrations to differentiate the metabolizable methionine contributions of rumen-protected methionine products.

N. L. Whitehouse

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06-24-2020

Abstract:

315
Using plasma sulfur amino acid concentrations to differentiate the metabolizable methionine contributions of rumen-protected methionine products.
N. L. Whitehouse*, A. R. Blanchard, S. M. Hollister, L. H. P. Silva. University of New Hampshire Durham, NH.

The objective was to investigate if the plasma AA dose-response method, using total sulfur AA (TSAA) concentrations as a % of TAA — SAA concentrations, could statistically differentiate the metabolizable Met content in 4 unique RP-Met products in lactating Holstein cows. Ten multiparous Holstein cows (175 � 59 DIM) were used in a replicated 5 � 5 Latin square with 7-d experimental periods. The 5 treatments were: 1) a negative control (CON); 2) 24 g/d Met from Smartamine M (SMM; Adisseo; Met bioavailability ≥80%); 3) 24 g/d Met from AminoShure-XM (AXM; Balchem); 4) 24 g/d Met from MetiPEARL (MPL; Kemin); and 5) 24 g/d Met from Timet (TMT; Vetagro). Intake and milk yield were measured daily. Blood was collected from the tail vein the last 3 d per period at 2, 4, 6 and 8 h after the 0500h feeding. Data were analyzed using MIXED and REG procedures of SAS. Significance was declared at P ≤ 0.05. Milk yield (37.1 kg/d) and DMI (25.6 kg/d) were not affected by treatment. Plasma Met, cystathionine/allocystathionine, and TSAA concentrations were increased for cows fed AXM compared with CON and MPL, and further increased for SMM compared with AXM (Table 1; P < 0.001). Based on comparison of dose-response slopes using TSAA expressed as a percentage of TAA-TSAA, AXM, MPL, and TMT were 35.0 (�4.0), 9.3 (�3.7), and 24.0% (�7.2) as effective as SMM in providing metabolizable Met.Table 1. Plasma AA concentrations, dose-response slopes, and calculated concentrations of metabolizable Met in RP-Met supplements

ItemCONAXMMPLSMMTMTSEMP-value
Methionine, �M24.6d29.1b25.2cd43.6a27.4bc0.87<0.001
Cystine, �M20.120.720.021.220.00.360.10
Cystathionine/Allocystathionine, �M1.81c2.02b1.84c2.61a1.98bc0.08<0.001
Homocystine, �M2.542.412.602.582.430.260.98
Taurine, �M46.248.242.552.545.73.680.42
TSAA, �M95.4c102.5b92.3c122.6a97.7bc2.71<0.001
Slope TSAA (%TAA − TSAA)0.0192b0.005c0.0547a0.131b0.002<0.001
Metabolizable Met, g/kg120242636108
a—dMeans within rows differ at P < 0.05.1Analyzed Met content of products: AXM 72.3%, MPL 56.0%, SMM 79.5%, and TMT 56.3%.

Keywords: plasma, sulfur amino acids, bioavailability.