79 Prenatally Stressed Brahman Bulls Produced Embryos with Decreased Embryonic Development
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abstract
AbstractThe objective of this experiment was to determine if semen collected from prenatally stressed (PNS) Brahman bulls altered early embryonic development compared to control (CON) bulls. Prenatal stress was achieved by transporting Brahman dams for 2h on d60, 80, 100, 120, and 140 (5d) of gestation. Semen collected from sexually mature male offspring born to transported (PNS; n=4) or non-transported (CON; n = 5) dams was used to fertilize abattoir derived cumulus oocytes complexes (n = 81-100/bull in 2 wells) in an in vitro setting to monitor early embryonic development. Fertilization took place for 18-20h (day 0). Then, putative zygotes were cultured for 8 days. Cleavage was recorded on d3, the number of 1, 2-6, 8-16, or 16-32 cell embryos was recorded on d5, and the number of blastocysts and degenerated embryos was recorded on d8. A subset of blastocysts from PNS (n = 12) or CON (n = 23) bulls were immunolabelled to differentiate inner cell mass (ICM) and trophectoderm (TE). Differences in early embryonic development and ICM:TE ratios were determined using the GLIMMIX procedure in SAS (9.4) with well as a fixed effect. On d3, the percentage of oocytes that cleaved did not differ (P = 0.2660) between treatments. Treatment also had no effect on the percentage of 1 (P = 0.1622), 2-6 (P = 0.1138), 8-16 (P = 0.2722), or 16-32 (P = 0.5586) cell stage embryos on d5 nor the percent of degenerated embryos (P = 0.1130). However, the percentage of embryos that developed to a blastocyst by d8 differed (P = 0.0291) between treatments such that oocytes fertilized by sperm produced by PNS bulls (28%) were less likely to advance to the blastocyst stage compared to CON bulls (35%). The ICM:TE ratio did not differ (P = 0.6484) between treatments. Thus, PNS Brahman bulls do not have an obvious problem to fertilize but may produce sperm with epigenetic modifications that hinder blastocyst formation.
