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. / Master of Science / The incidences of pregnancy loss in both beef and dairy cattle industries are profound and are upwards of 60 percent. Financial stability for both of these industries revolves closely around the ability of cattle to give birth to a live calf annually. While artificial insemination (AI) has been heavily adopted and utilized widely in the dairy industry, the use of in vitro produced (IVP) bovine embryos has shown promise in lessening some of the stresses placed on impregnating cattle. The IVP of bovine embryos serves as a strong model to understand how pregnancy losses occur. Briefly, IVP involves the collection of eggs from donor animals, and subsequent fertilization to mimic what occurs within the animal naturally. A disadvantage of in vitro produced embryos is their reduced likelihood to establish pregnancy after transfer into recipient animals. Interleukin-6 (IL6) was recently identified as a pro-developmental factor that may improve the quality and post-transfer competency of in vitro produced embryos. The objective of this work was to determine if IL6 supplementation during in vitro culture improves post-transfer fetal development. Oocytes (i.e. eggs) were retrieved from slaughterhouse-derived ovaries and subjected to in vitro maturation and fertilization. On day 5 post-fertilization, embryos were treated with either 0 (CONT; 1% BSA) or 100ng/mL recombinant bovine IL6. On day 7.5 post-fertilization, individual embryos (blastocyst stage) were loaded into transfer straws. Estrous synchronized beef (n = ) and dairy (n = ) cow recipients were allocated into treatment groups in the following manner. A subset of cows from each group underwent fixed-time AI (n=37). Remaining cows underwent embryo transfer (ET) in the uterine horn ipsilateral to a corpus luteum; 51 of these cows received a CONT embryo and the remaining 35 cows received an IL6 embryo. Thus, there were three treatment groups: AI, CONT, and IL6. Embryo and fetal measurements were performed via transrectal ultrasonography weekly from day 28 to 56, these included crown-rump length, crown-nose length, abdominal diameter, and amniotic vesicle. Pregnancies that remained throughout the entirety of the experiment 40.0% for IL6 (14/35); 19.6% for CONT (10/51); and 32.4% for AI (12/37). In summary, IL6 treatment of embryos produced pregnancies with characteristics more similar to the current industry standard of AI, rather than conventionally cultured embryos (CONT), supporting the hypothesis that IL6 supplementation to bovine embryos on day 5 post-fertilization improves developmental competency of in vitro produced embryos.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/106804 |
| Date | 09 June 2020 |
| Creators | Seekford, Zachary Kent |
| Contributors | Animal and Poultry Sciences, Ealy, Alan Dale, Daniels, Kristy Marie, Mercadante, Vitor R. G. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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