279VASCULAR MORPHOMETRY OF BOVINE PLACENTOMES IN LATE GESTATION FROM EMBRYOS PRODUCED IN VIVO OR IN VITRO

The role of the vascular supply in the development of placentas from embryos produced in vitro is poorly understood. The objective of this study was to determine the effects of in vitro embryo production on morphometry of blood vessels within fetal (cotyledonary) and maternal (caruncular) components of the placentome during late gestation. In vivo-produced embryos were recovered from superovulated Holstein cows on Day 7 after estrus. For in vitro embryo production, oocytes were aspirated from the ovaries of Holstein cows, matured in vitro, and then fertilized. Presumptive zygotes with their cumulus cells were transferred into M-199 with 10% estrus cow serum and cultured for 168h post-insemination. Semen from the same Holstein sire was used for the production of in vivo and in vitro embryos. Single blastocysts from each production system were transferred into the uteri of heifers. On Day 222 of gestation, fetuses and placentas were recovered in utero (in vivo, n=12; in vitro, n=12). Placentomes were collected, fixed and sectioned. Fetal and maternal blood vessels were identified within placentome sections using immunocytochemistry for vascular endothelial growth factor (VEGF) protein. A total of 4.8×105μm2 of tissue were examined from each placentome. Stereological methods were used to determine the volume densities of fetal and maternal blood vessels. Data were analyzed by GLM procedures. Fetuses were heavier (P=0.03) in the in vitro group (20.7±1.0kg, LS mean±SEM) compared to the in vivo group (17.3±1.0kg). Placentas were also heavier (P=0.06) for the in vitro group (2.5±0.2kg) compared to the in vivo group (2.0±0.2kg). Placental efficiency, calculated as fetal weight/placental weight, was similar between the two treatment groups (9.0±0.5 and 8.9±0.5 for in vivo and in vitro, respectively). Fetal vascular volume density in placentomes was not different between the two treatment groups (5.4±0.3% and 5.4±0.3% for in vivo and in vitro, respectively). In contrast, maternal vascular volume density was greater (P=0.02) for placentomes in the in vitro group (5.9±0.3%) compared to in vivo controls (4.9±0.3%). In summary, compared to placentomes from embryos produced in vivo, placentomes from embryos produced in vitro had similar volume density of fetal vessels, but had significantly increased volume density of maternal vessels. Supported by the State of North Carolina.