Interleukin-6 Supplementation Improves Post-Transfer Embryonic and Early Fetal Development of in vitro Produced Bovine Embryos

In vitro produced (IVP) bovine embryos are useful for investigating the mechanisms affecting early embryonic failure. The work in this thesis explored how interleukin-6 (IL6), an embryokine that increases inner cell mass (ICM) influences post-transfer embryonic survival and development of the embryo-proper and fetus. Four replicates of slaughterhouse-derived cumulus oocyte complexes underwent in vitro maturation and fertilization. On day 5 post-fertilization, embryos were treated with either 1% Bovine Serum Albumin (BSA) (CONT) or 100ng/mL recombinant bovine IL6 with 1% BSA (TRT). On day 7.5 post-fertilization, individual blastocysts were loaded into transfer straws. Beef and dairy cow recipients were synchronized with the day of in vitro fertilization using a 7-d CO-Synch protocol. A subset of cows from each group underwent fixed-time artificial insemination (AI) (n=37). The remaining cows underwent embryo transfer (ET) in the uterine horn ipsilateral to a corpus luteum (CL) (IL6 n=35; CONT n=51). Embryo and fetal measurements were performed via transrectal ultrasonography weekly from days 28-56 post-insemination, respectively. Overall pregnancy rates were 40.0% IL6; 19.6% CONT; and 32.4% AI. Crown-rump lengths (CRL) were reduced (P<0.05) in CONT pregnancies when compared with IL6 and AI at days 28, 35, 42, and 56. A tendency (P=0.057) for larger abdominal diameters was detected between IL6 and CONT groups. Also, IL6 had larger crown-nose lengths than CONT (P<0.05) and tended to be larger than AI (P=0.07). In summary, IL6 treatment produced pregnancies resembling AI-generated pregnancies more so than conventionally cultured embryos, supporting the hypothesis that IL6 improves developmental competency of IVP embryos.