Regulation of Milk Protein Synthesis by Free and Peptide-Bound Amino Acids in Dairy Cows.

Hongyun Liu,Fengqi Zhao,Miaomiao Zhou,Lianbin Xu

doi:10.3390/biology10101044

Hongyun Liu, Fengqi Zhao + Show 2 more

Open Access

https://doi.org/10.3390/biology10101044

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Abstract

Simple SummaryFree and peptide-bound amino acids are the main substrates for milk protein synthesis in the mammary gland. The milk protein concentration and yield of dairy cows are regulated by free and peptide-bound amino acids. The present article reviews the effects of free and peptide-bound amino acid supply on milk protein synthesis and their underlying mechanisms.Milk protein (MP) synthesis in the mammary gland of dairy cows is a complex biological process. As the substrates for protein synthesis, amino acids (AAs) are the most important nutrients for milk synthesis. Free AAs (FAAs) are the main precursors of MP synthesis, and their supplies are supplemented by peptide-bound AAs (PBAAs) in the blood. Utilization of AAs in the mammary gland of dairy cows has attracted the great interest of researchers because of the goal of increasing MP yield. Supplying sufficient and balanced AAs is critical to improve MP concentration and yield in dairy cows. Great progress has been made in understanding limiting AAs and their requirements for MP synthesis in dairy cows. This review focuses on the effects of FAA and PBAA supply on MP synthesis and their underlying mechanisms. Advances in our knowledge in the field can help us to develop more accurate models to predict dietary protein requirements for dairy cows MP synthesis, which will ultimately improve the nitrogen utilization efficiency and lactation performance of dairy cows.

Highlights

Milk has important nutritional properties that are beneficial to the health and growth of infants [1,2]
The present review will focus on the regulation of Milk protein (MP) synthesis by free AAs (FAAs) and peptide-bound AAs (PBAAs) in dairy cows
Increasing essential amino acids (EAAs) supply to the mammary gland (MG) is the basis of most dietary treatments to enhance MP content or MP yield

Summary

Introduction

Milk has important nutritional properties that are beneficial to the health and growth of infants [1,2]. Milk protein (MP) can provide essential amino acids (EAAs) and has high nutritional value. Amino acids (AAs) are the building blocks of protein synthesis; they suppress protein catabolism and serve as substrates for gluconeogenesis [2,3]. Mammary-derived MPs consist of casein and whey proteins [5,6]. Mammary-derived MPs are synthesized using substrates extracted from blood as free AAs (FAAs) and peptide-bound. The amount and balance of AAs are the most important factors for MP synthesis [14,15]. Absorption and utilization of FAAs and PBAAs by the mammary gland (MG) can regulate MP synthesis. The present review will focus on the regulation of MP synthesis by FAA and PBAA in dairy cows

Determination of Limiting AAs

EAAs Promote MP Synthesis

AA Balance

PBAAs Are Involved in MP Synthesis

AA Transport Systems

Role of AAs in Regulation of MP Synthesis

PBAA Transport Systems

Role of PBAAs in MP Synthesis

Findings

Conclusions and Perspectives