Refining plasma dose response techniques for bioavailability of rumen protected amino acids

Key Findings

Rumen-protected amino acid products have been documented to have animal performance and nutritional benefits for optimizing concentrations of amino acids. This is needed to improve lactational performance, health and reproduction, dairy nutritional models and emissions footprint.

As more rumen-protected amino acid supplements come into the marketplace, this study provides estimates of lysine and methionine bioavailability from numerous tested RP-AA concentrations in those supplements. Of the tested products, Smartamine M provides the highest relative bioavailability of both amino acids.

About the Co-Author

A photo of NHAES researcher Nancy Whitehouse

Nancy Whitehouse, Research Assistant Professor of Agriculture, Nutrition, and Food Systems

Contact information:, 603-862-1349

This research was published in the INSPIRED: A Publication of the New Hampshire Agricultural Experiment Station (Winter 2021)

Researcher: N. Whitehouse

Lysine (Lys) and methionine (Met) are the two most limiting amino acids (AAs) in typical North American dairy diets (NRC, 2001). Several rumen-protected Lys (RP-Lys) and rumen-protected methionine (RP-Met) feed supplements are available in the marketplace for increasing concentrations of Lys and Met in metabolizable protein. However, successful use of rumen protected AA products requires accurate and reliable estimates of AA bioavailability because RP-AA nutrients are expensive. This study refines the plasma-free dose response technique to get reliable estimates of relative bioavailability of RP-AA supplements.

Limited research indicates that the apparent availability of Lys and Met to ruminants (i.e., bioavailability) from RP-AA supplements varies widely (Berthiaume et al., 2000; Ji et al, 2015), making reliable estimates of Lys and Met bioavailability essential when considering the purchase and use of these products. Rulquin and Kowalczyk (2003) were the first researchers to suggest using a plasma free AA dose response method to determine bioavailability of AA in RP-AA.

Although most suppliers provide estimates of Lys and Met bioavailability for their RP-AA supplements, these bioavailability values were not obtained using standardized techniques or methodologies. Without a standardized procedure for differentiating RP-AA supplements under feeding conditions closer to commercial practices, producers and industry personnel have no reliable information to make decisions about which RP-AA supplement to use based on price and amount of absorbable Lys and/or Met.

All procedures related to animal care were conducted with the approval of the University of New Hampshire Institutional Animal Care and Use Committee. Cows were housed at the Fairchild Dairy Teaching and Research Center in a naturally ventilated tie-stall barn, fed individually, and had continuous access to water.

High producing lactating multiparous Holstein cows were fitted with ruminal cannula to allow for abomasal infusion of the “unprotected” AA. Experiments with a minimum of seven-day periods were used. RP-AA supplements were mixed in a portion of the total mix ration 8 hours before feeding. Blood samples are collected the last three days of each period at 2, 4, 6, and 8 hours after morning feeding. Deproteinized plasma samples are pooled within day (across four sampling times) for each cow before AA analysis. The data represent 20 Lys experiments involving 40 products and 11 Met experiments involving 21 products. Tables 1 and 2 show the relative bioavailabilities for the tested RP-Lys and RP-Met products.

Table 1: Relative bioavailability of RP-Lys

Table 2: Relative bioavailability of RP-Met