173 Effects of aggregated protein content in sperm head on pre-implantation development of bovine embryos

Female reproductive performance has been extensively studied; however, sire contribution on embryo production has largely been overlooked. It is well established that sperm induces oocyte activation after fertilization; nevertheless, little is known about the role of the male beyond fertilization. Previous data from our group suggest that bovine sperm with high aggregated protein content might be related to fertility. Aggresome content is expected to be found in the tail, but high concentrations of protein in the head might impair embryo development. The objective of this study was to identify if aggregated protein content in sperm head interferes with pre-implantation embryonic development. Briefly, flow cytometry analysis was performed in 32 sires; two straws per bull were used and an average of 640 sperm cells per sire were evaluated. Sires were divided by the percentage of the population with either high or low aggregated protein content on the sperm head. Quartile 1 had the lowest and quartile 4 the highest amount of aggresome, respectively. Sires from quartile 4 had 21%–45% of their overall population with high aggresome content. In a second experiment, two sires were selected with either low or high aggregated protein content in the head. Following standard procedures from our group, two rounds of in vitro production were performed. A total of 140 presumptive zygotes for the high aggresome sire and 124 for the low aggresome sire were selected for culture. Cleavage rate was assessed at Day 3 post-insemination and blastocyst production evaluated at Day 7.5 post-insemination. Statistical analysis was done by analysis of variance using SAS v 9.4. There was no difference in cleavage (P = 0.21) between low and high aggresome bulls (69.48% ± 4 vs 62.23% ± 4, respectively). Likewise, no difference (P = 0.15) was found for blastocyst rate (30.02% ± 4.1 vs 22.21% ± 3.5). The lack of a significant difference between phenotypes could be explained due to the small sample size in our data since blastocyst rate from the high aggresome sire seemed to be negatively impacted. Our preliminary findings suggest that there might be an association of high aggresome content in the sperm head with lower embryo production and more rounds of embryo production are expected to be added to fully delineate this phenotype. Sperm bovine aggresome content has not been characterised before, making this study a novel approach to identify fertility markers that would be more helpful than routine morphology and motility analyses. Further studies will be required to fully understand the mechanisms by which embryos are being affected by the two different phenotypes.