166. Effects of in-vitro Embryo Production on Placental Steroid Hormone Synthesis, Placental Morphology, Calf Vigor, and Calf Growth Through Weaning.

Abstract In-vitro embryo production has become popular in both research and production settings. In-vitro derived pregnancies are reported to have longer gestation lengths; however, the mechanism responsible for this phenomenon is unknown. Steroid hormones play a role in the onset of parturition and previous work has documented changes in circulating steroid hormones in cows carrying an in-vitro produced pregnancy compared to cows carrying a pregnancy produced through artificial insemination or natural service. We hypothesized that embryo origin would affect the cascade involved in placental steroid production, placental morphology, calf vigor, and calf growth. Cows carrying an artificial insemination derived embryo (AI = 23), natural service pregnancy (NS = 23), or in-vitro produced embryo (IVP = 23) were randomly selected for calf vigor and growth assessments. Cow-calf pairs were monitored from the onset of labor to the following intervals: time of birth, vigor score at 30 minutes of age, time of standing (minimum of five seconds), time of nursing, and time of placental expulsion. Placentas (n = 68; AI = 23; IVP = 22; NS = 23) were collected immediately following expulsion, weighed, and three representative cotyledons were removed and processed for RT-qPCR. One placental collection (IVP = 1) was missed because personnel were unavailable due to processing a prior placenta. The following genes were evaluated to determine the differences in placental estrogen synthesis: CYP19, CYP17, COX-II, CYP11A1, SULT1E1, and HSD3b. All data were analyzed in R Studio using a general linear model with Gaussian distribution and ANOVA F-statistic. Placental weight was greater in IVP pregnancies compared to both AI and NS (P = 0.03). Non-gravid cotyledon number was fewer in IVP and NS pregnancies compared to AI pregnancies (P = 0.04), while total cotyledon weight was greater in the IVP and NS pregnancies (P = 0.03). However, no differences were observed in cotyledon diameter or circumference (P ≥ 0.24). A group ´ calf sex interaction was observed for calf birth weight, time between birth and nursing, and time between standing and nursing (P ≤ 0.05). IVP bull calves took less time to nurse following birth compared to NS bulls (P = 0.04) but were similar when compared to AI bulls (P = 0.96). No differences were observed in CYP19, CYP17, COX-II, CYP11A1, SULT1E1, or HSD3b expression between IVP and AI or IVP and NS (P ≥ 0.13). Overall, embryo origin increased placental weight, total cotyledon weight, IVP heifer birth weights, and IVP calves demonstrated greater vigor once standing; however, no differences were identified in placental steroid gene expression. These results indicate that placental steroid hormone synthesis may not be driving longer gestation length; therefore, another mechanism may be contributing to the longer gestation lengths observed and will need to be studied.