The age of the bull influences the transcriptome and epigenome of blastocysts produced by IVF

Genetic selection for the best suited offspring drives the dairy industry to use young genitors and assisted reproductive technologies (ART) to reduce generation intervals. However, sperm samples collected from peri-pubertal bulls have lower counts and quality compared to samples from adult bulls. Moreover, our previous study identified differentially methylated regions (DMRs) in sperms from early-, peri- and post-pubertal bulls. The aim of this study was to further investigate the impacts of paternal age on early embryos. To achieve this, we evaluated the transcriptome and the epigenome of bovine blastocysts generated from spermatozoa of bulls at 10, 12, and 16 months of age and used in vitro fertilization (IVF) of oocytes recovered from the same adult cows. A total of 259 probes were differentially expressed and 6953 probes were differentially methylated in the 10- vs 16-month and the 12- vs 16-month groups. Ingenuity Pathway Analysis (IPA) of transcriptomic data demonstrated that energy-related pathways such as oxidative phosphorylation, EIF2 signaling, and mitochondrial dysfunction were affected the most by the age of the bull. Meanwhile, IPA analysis of the epigenome revealed that protein kinase A signaling, RAR activation, and other pathways were influenced by paternal age. Overall, we showed that the bull's age mainly influenced metabolism-related pathways in blastocysts, and this could therefore impact subsequent development.