Urea influences amino acid turnover in bovine cumulus-oocyte complexes, cumulus cells and denuded oocytes, and affects in vitro fertilization outcome

Rasoul Kowsar,Ahmad Riasi,Vahid Norozian Iranshahi,Akio Miyamoto,Nima Sadeghi

doi:10.1038/s41598-018-30774-2

Abstract

High-protein diets often lead to an increase in urea concentration in follicular fluid of dairy cows, which may reduce oocyte competence. In the present study, maturation media were supplemented with urea (0, 20, 40 mg/dl), and amino acids (AAs) turnover was evaluated in the 24-h spent media of specimens (cell types), bovine cumulus-oocyte complexes (COCs), cumulus cells (CCs), or denuded oocytes (DOs). The main effects of urea and cell type, and their interaction were significant on the individual turnover (expect threonine, glycine, and tyrosine) and total turnover, depletion, and appearance of AAs. The results showed a high level of urea and DOs increased the depletion of all AAs and that of essential and non-AAs, respectively. Sensitivity analysis revealed the highest sensitivity of isoleucine, lysine, and tryptophan to urea, especially in DOs. Principal component analysis (PCA) evaluated the strong correlations between the turnover of: (1) glutamine, aspartic acid or glycine, and developmental competence and fertilization of COCs; (2) serine, isoleucine, valine or glutamic acid, and cleavage rate of DOs; and (3) serine, glutamine, aspartic acid or alanine, and CCs viability. In conclusion, urea significantly changed the turnover of AAs by COCs, CCs and DOs, and reduced the subsequent developmental competence of bovine oocytes.

Highlights

To support the potential of milk production, high-producing dairy cows are often fed high-protein diets (17 to 19% crude protein1) and may, in turn, experience a reduction in fertility[2]
We hypothesized that urea at: (1) 0 mg/dl; (2) 20 mg/dl; and (3) 40 mg/dl may differently change the turnover of amino acids (AAs) in bovine cumulus-oocyte complexes (COCs), cumulus cells (CCs), and denuded oocytes (DOs)
The lowest turnover of valine, histidine, methionine, tryptophan, and phenylalanine was found by COCs while DOs had the lowest turnover of leucine and isoleucine, and CCs had the lowest turnover of threonine and lysine (Fig. 1)

Summary

Introduction

To support the potential of milk production, high-producing dairy cows are often fed high-protein diets (17 to 19% crude protein1) and may, in turn, experience a reduction in fertility[2]. Sinclair et al.[5] reported that cytoplasmic and nuclear maturation of oocyte were sensitive to nutrition conditions They found that oocytes collected from heifers fed high BUN-generating diets had a lower developmental competence. We hypothesized that urea at: (1) 0 mg/dl; (2) 20 mg/dl (equivalent to 9.3 mg/dl BUN found in healthy dairy cows under low protein diets); and (3) 40 mg/dl (equivalent to 18.7 mg/dl BUN found in healthy dairy cows fed high-protein diets7,18) may differently change the turnover of AAs in bovine COCs, CCs, and DOs. marginal effects and principal component analysis (PCA) were employed to estimate the sensitivity of amino acids to urea, and to identify the association between amino acid turnover and the viability of cumulus cells or subsequent developmental competence of COCs and DOs

Methods

Results

Conclusion