Work

Trans-organ net fluxes of essential amino acids and their calculated efficiency of utilization in dairy cows: A meta-analysis

Year: 2026

Type: review

Study designs: Systematic Review, Meta-Analysis

Abstract: The 8th revision of the Nutrient Requirements of Dairy Cattle by the National Academies of Sciences, Engineering, and Medicine (NASEM, 2021) introduced the concept of target efficiency, based on the calculation of the efficiency of utilization (EffU) of EAA.This EffU calculated using the NASEM approach (NASEM EffU ) represents the sum of each EAA in protein secretions and accretions divided by the metabolizable supply of each EAA, excluding the EAA contribution to endogenous urinary losses (assumed to have an EffU of 100%).Trans-organ net fluxes, across the portal-drained viscera (PDV), the liver and the mammary gland were used to estimate the potential catabolism of EAA across these tissues, summed to yield the whole-body EAA catabolism from which inefficiency of use, and therefore EffU, can be calculated, the latter being referred to as Measured EffU .Therefore, those measurements based on trans-organ net fluxes give us the opportunity to verify how the theoretical NASEM EffU compares with Measured EffU in lactating dairy cows, which was the objective of the current metaanalysis.The data set needed to be divided between studies where post-splanchnic supply of EAA was insufficient to account for mammary uptake and studies where it was adequate, resulting in one category for cows with DIM ≤30, and another for cows with DIM >30, referred to as cows in early lactation and later lactation, respectively.For cows in later lactation, NASEM EffU and Measured EffU agreed well (concordance correlation coefficient averaging 68%) based on significant catabolism of: (1) Group 1 AA (His, Met, and Phe) in the liver; (2) Ile, Leu and Val by the PDV, non-mammary peripheral tissues, and the mammary gland; (3) Lys in the liver, non-mammary peripheral tissues, and the mammary gland; and (4) Thr in the PDV, liver and the mammary gland.There was, however, a significant mean bias between NASEM EffU and Measured EffU for Met, the latter being smaller than NASEM EffU .This would suggest that the part of Met liver removal is used for the synthesis of metabolites, such as cysteine, glutathione, and taurine, not needing other EAA and not included into export proteins.This might suggest that the target EffU of Met proposed by NASEM (2021) should be reduced.For cows in early lactation, the concept of NASEM EffU does not apply for most of the EAA.Mathematically, relationships between NAS-EM EffU and Measured EffU were poor in these animals, with concordance correlation coefficient smaller than 30% for His, Met, Phe, Lys and Val.Indeed, unknown endogenous supply from body protein mobilization invalidates the quantification of the actual contribution supporting protein export.The sites of EAA removal, however, remained the same throughout lactation except for the non-mammary peripheral tissues being a source of endogenous supply for all EAA, rather than a site for the catabolism for Ile, Leu, Lys and Val, as observed for cows in later lactation.

Source: Journal of Dairy Science

DOI: 10.3168/jds.2025-27795

Authors: R. Martineau, D.R. Ouellet, G.E. Lobley, H. Lapierre

Institutions: Agriculture and Agri-Food Canada, Sherbrooke Research and Development Centre, University of Aberdeen

Language: English

Topic: Ruminant Nutrition and Digestive Physiology

Subfield: Agronomy and Crop Science

Field: Agricultural and Biological Sciences

Domain: Life Sciences

SDG: Zero hunger

Open Access status: gold

Estimated APC paid: $3,500