Amino acid concentrations in uterine fluid during early pregnancy differ in fertile and subfertile dairy cow strains.

The objective of this study was to determine if free AA concentrations in uterine luminal fluid (ULF) and plasma differed between dairy cow strains that differ phenotypically for fertility and to evaluate the effect of the presence of a conceptus on ULF AA concentrations. Uterine luminal fluid was obtained postmortem from cows characterized on the basis of genetic ancestry as fertile (n=11) or subfertile (n=11) strains. At slaughter, cows were at a similar stage of lactation (fertile, 85 ± 1 d and subfertile, 87 ± 1 d postpartum, respectively). Cows were slaughtered on either d 17 of the estrous cycle [nonpregnant (n=10): fertile n=5; subfertile n=5] or d 17 of pregnancy [10d after embryo transfer, which was undertaken 7d after estrus (n=12, pregnant): fertile n=6, subfertile n=6]. Uterine luminal fluid was collected from each uterine horn of the pregnant (gravid and nongravid horns) and nonpregnant (horn ipsilateral and contralateral to the corpus luteum) cows. Plasma harvested on the day of slaughter and ULF samples were analyzed for AA determination using HPLC. The main effects of genetic strain, reproductive status, and their interactions on ULF and plasma AA content were tested. Additionally, the effect of uterine horn on ULF AA was tested for the pregnant and nonpregnant cows. Reproductive status had the greatest effect on AA concentrations in ULF. The concentrations of Leu, Met, Phe, Val, 1-methyhistidine, Asp, essential, ketogenic, and branched-chain AA, and those AA classified as both glucogenic and ketogenic were greater in the ULF collected from pregnant cows, with taurine being lower. Additionally, we observed effects of uterine horn and genetic strain × uterine horn interaction for ULF AA concentrations. Concentrations of the essential AA plus Met and Phe were greater in the ULF from the gravid horn, irrespective of strain. The ULF from the gravid horn of fertile cows contained the greatest concentrations of nonessential, glucogenic, branched-chain AA, and Leu, Thr, Ala, Ser, and Asp. With the exception of Asp, plasma AA profiles were not different in fertile and subfertile strains. These data support the hypothesis that reproductive status modifies the AA profiles of the ULF and that these profiles differ in fertile and subfertile genetic strains. Successful pregnancy depends on the complex interactions between the developing conceptus and uterine environment. Understanding the mechanisms contributing to maternal-conceptus communication using models with divergent fertility phenotypes could provide information regarding novel mechanisms to improve dairy cow fertility.