254. Award Talk: Paternal Overnutrition in Bulls Impaired Blastocyst Development and Decreased Preimplantation Conceptus Length with Minimal Changes to Conceptus and Endometrial Transcriptome.

Abstract Bull overnutrition has been shown to induce an obese-like phenotype, negatively impacting semen quality; however, the contributions of paternal overnutrition on pre-implantation conceptus development remain unknown in the bovine. The objective of this study was to investigate the impact of paternal overnutrition on elongation and transcriptomic profiles of day 15 preimplantation conceptuses and ipsilateral inter-caruncular endometrial (ICE) tissue. Half- sibling yearling beef bulls (n = 29) were used in a completely randomized design and assigned to 1 of 2 dietary treatments for 114 days: 1) Moderate Gain (MG), diet formulated to promote an average daily gain of 1.2 kg/day, or 2) High Gain (HG), diet formulated to promote an average daily gain of 1.8 kg/day. At the end of the feeding period, semen was collected, cryopreserved, and utilized to produce embryos in vitro. Fresh embryos (2–5 per recipient) were transferred into nonlactating beef cows on day 7.5, and conceptus collection was performed on day 15 of gestation using either in vivo uterine flushing or postmortem uterine recovery. Filamentous conceptus length was assessed, and a subset of conceptuses (n = 19) and ICE (n = 13) samples were subjected to RNA sequencing, and differential gene expression was evaluated using a false discovery rate (FDR) threshold of ≤ 0.10. Embryos sired by HG bulls had decreased (P = 0.023) cleavage rates compared with MG bulls (59.6 vs. 69.3%), as well as decreased (P = 0.018) blastocyst rates when expressed relative to oocytes (20.2 vs. 28.1%) and a tendency (P = 0.084) for decreased blastocyst rates relative to cleaved structures (34.4 vs. 42.2%). Conceptuses sired by HG bulls tended to have reduced total length (4.6 ± 3.39 vs. 13.3 ± 2.51cm), length per embryo transferred (1.8 ± 0.79 vs. 3.6 ± 0.58 cm), and length per conceptus recovered (2.2 ± 0.90 vs. 4.2 ± 0.66 cm; P ≤ 0.098). Transcriptomic analysis of filamentous conceptuses identified 12 differentially expressed genes (10 upregulated and 2 downregulated) between sire treatments (FDR ≤ 0.10), whereas no differentially expressed genes were detected in ICE samples. In summary, paternal overnutrition of young bulls impaired early embryo development, resulting in reduced embryo production through the blastocyst stage and decreased conceptus length, while transcriptomic differences in the conceptus and maternal endometrium at day 15 of gestation were minimal.