Date of Award

Fall 2026

Abstract

There continues to be gaps in comparing the bioavailability of different rumen-protected methionine and lysine products. Many techniques have been developed to analyze these products with in vivo techniques considered the gold standard. The following three studies were proposed to determine the relative bioavailability value of products containing lysine and various forms of methionine using the plasma dose-response method as described by Whitehouse et al., 2017. Trial one compared two levels (18 g/d and 36 g/d) of L-Met infusion and fed LipoActiv L-Met 60. Trial two compared infusions of, and products containing, DL-Met and HMTBa (2-hydroxy-4-(methylthio)butanoic acid). Trial three used noncannulated cows to analyze fed RP-Lys products against a positive control of Smartamine ML. All trials were designed as Latin squares with 7-d periods. Products were fed in three daily aliquots at 0500, 1300, and 2100 h with the basal diet. Blood was collected from the coccygeal vein the last 3 d of each period at 2, 4, 6 and 8 h after the morning feeding (0500 h). Amino acids in plasma were determined using HPLC. Data showed a normal distribution of values. Data were analyzed using PROC MIXED to generate means for total sulfur AA (TSAA) which were then used in the REG procedures of SAS to generate the linear regression variables. Significance was declared at P ≤ 0.05. Bioavailability of treatments in trials one and two, were calculated as [(slope of RP-Met / slope of infusion) x100] ± CI. Bioavailability of treatments in trial three was calculated as {[(slope of RP-Lys / slope of Smartamine ML) x 100] x 0.80} ± CI to account for the known bioavailability of Smartamine ML (80 ± 3.5%) as established using the plasma dose response method with lysine infusion serving as the positive control in ruminally-cannulated cows. Trial 1 noted an interaction between treatment and milk protein %, but milk yield and DMI were not impacted by treatments in the other trials. The relative bioavailability of each product was LipoActiv L-Met 60 43.4 ± a standard error of 2.5%, Mepron 34.7 ± 3.3%, MetaSmart Dry 50.6 ± 2.8%, Sandirumet 47.1 ± 1.5%, Smartamine M 80.3 ± 2.1%, 48.4 ± 6.9% for AjiPro-L 3G, 23.9 ± 2.4% for AminoShure XL, 46.7 ± 4.4% for LysiGem Extend, and 31.6 ± 8.9% for Lys Sila 50. The bioavailability for MetaSmart Dry when calculated using changes in plasma TSAA+HMTBa % of (TAA-TSAA+HMTBa) was 50.4 ± 3.0%, which was similar to the bioavailability of 50.6 ± 2.8% when using TSAA % of (TAA-TSAA). The overall results of all studies provide supporting evidence for the reliability and repeatability of the plasma dose-response technique.

Document Type

Master's Thesis

First Advisor

Nancy L Whitehouse

Second Advisor

Peter S Erickson

Third Advisor

Claira Seely

Department or Program

Animal and Nutritional Sciences

Degree Name

Master of Science

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