AabstractOviductal (OF) and uterine (UF) fluids from slaughterhouse bovine reproductive tracts selected around the pre-implantation period of embryo development were analyzed for twenty-four amino acids. Amino acid concentrations in the OF and UF fluids were compared with those in a base culture medium (KSOM) supplemented with either FCS or Minimum Essential Medium amino acids (MEM-aa) in addition to PVA, FCS or BSA. Concentrations of 23 amino acids in UF were significantly (P<0.05) higher than those provided by KSOM supplemented with any of the supplements. Cystine was the only amino acid that was supplemented in comparable levels to those in UF. However, OF levels of CYS were higher than those in UF and supplemented KSOM. Compared to amino acid levels in OF, the supplementation of KSOM with either FCS or MEM-aa in addition to PVA, FCS or BSA resulted in significantly (P<0.05) lower levels of 15, 13, 13 and 10 amino acids, respectively. The results showed that non-essential (NE) amino acids are the most abundant in both OF and UF, and compared to essential (E) amino acids, they were present in both fluids at ratios of 5:1 and 2:1, respectively. Glycine (14.1 mM), GLU (5.5 mM) and ALA (3.7 mM) were present in high concentrations and comprised 72% of the free amino acid pool of OF. In the uterine fluid, concentrations of GLY (12.0 mM), GLU (4.2 mM), ALA (3.1 mM) and SER (2.7 mM) were the highest. Concentrations of all non-standard amino acids were significantly (P<0.05) higher in UF compared to KSOM supplemented with either FCS or FCS in addition to MEM-aa. In OF, only CIT and -ALA were significantly (P<0.05) higher in concentrations compared to KSOM under similar supplementation. In conclusion, concentrations of most of the amino acids in the bovine reproductive tract were substantially higher than those supplemented in culture media commonly used for in vitro development of bovine preimplantation embryos. Adjustment of amino acid concentrations in the culture medium according to those found in the bovine reproductive tract may improve embryo development in vitro. Further culture studies are currently investigating this hypothesis.