Association Between In Vitro Blastocyst Production and Blood Amino Acid Levels in Bovines

This study explored the association between blood amino acid (AA) levels at ovum pick-up (OPU) and bovine embryo formation. The oocytes from each heifer were harvested, matured in vitro for 24 h, and fertilized independently. The heifers were divided into two groups based on blastocyst formation: those that produced at least one blastocyst (the blastocyst group, n = 35) and those that did not (the failed group, n = 25). The concentrations of ornithine (p = 0.034), phenylalanine (p = 0.032), tryptophan (p = 0.038), tyrosine (p = 0.041), and lysine (p = 0.033) were lower in the blastocyst group than in the failed group. Compared with the failed group, the blastocyst group had higher blood threonine levels (p = 0.024). Using Spearman correlation, we found that threonine levels were the factor most associated (without causation) with blastocyst formation (r = 0.41, p = 0.012). Network analysis revealed an association (without causation) between blood threonine levels and successful blastocyst formation. The area under the receiver operating characteristic curve (AUC) analysis showed that blood threonine levels (0.69) followed by lysine (0.68) were associated with blastocyst formation. These data indicated an association between blood AA levels in heifers at the time of OPU and in vitro blastocyst formation. Notably, the findings are associative rather than causative and should be interpreted with caution.