Artificial insemination (AI) is the predominant reproductive technology in Japanese cattle breeding, particularly for genetic improvement of dairy and beef cattle. This review outlines the historical development, current status, and recent advances in semen production technologies for AI in Japan and addresses the remaining challenges and future directions. The adoption of AI accelerated after the Act on Improvement and Increased Production of Livestock was implemented in 1950, with frozen semen replacing liquid semen by the mid-1960s. Advances in cryobiology and genomic selection have improved breeding efficiency; however, fertility issues persist. In dairy cattle, conception rates have declined primarily due to high milk yield, negative energy balance, and heat stress. In beef cattle, particularly Japanese Black cattle, conception rates remain stable overall, but subfertile sires still occur despite normal post-thaw semen quality. Studies on sperm motility, acrosomal integrity, and genomic variants have identified a single nucleotide polymorphism (SNP) marker linked to extreme subfertility in Japanese Black bulls. Japan has developed innovative technologies such as the two-layer semen straw (FCMax), which enhances post-thaw sperm function through in-straw dilution and supplementation. Field trials have suggested potential improvements in conception rates; however, large-scale validation studies are still ongoing. Furthermore, sexed semen technology has been widely adopted in Japan and achieved conception rates comparable to those of conventional semen. Emerging challenges include labor efficiency in large-scale farms, prompting interest in improved thawing protocols or liquid semen alternatives. Future priorities include integrating genomic tools, refining cryobiological techniques, and implementing practical innovations to sustain cattle reproduction in evolving production systems.

To efficiently produce high-quality bovine calves by transferring embryos obtained from in vitro fertilization (IVF), it is important to evaluate their ability to conceive and their ability to develop into normal litters. In this study, we aimed to clarify the effects of timing and morphology of blastomere cleavage on the gene expression status of bovine IVF embryos. Bovine IVF embryos were classified in four categories, which were divided according to the time of the first blastomere cleavage and the presence or absence of direct cleavage. In addition, the gene expression profiles of these embryos were examined. The timing and morphology of the blastomere cleavage was involved in pre-implantation development and gene expression status of bovine IVF embryos. Our results indicate the possibility of multiple evaluations for bovine IVF embryos and the selection of the most suitable embryos for embryo transfer.

The conventional ovum pick-up method requires oocytes to be transported from local farms to the laboratory, where they undergo nuclear maturation. However, atmospheric conditions for oocyte transportation differ from those for normal oocyte maturation in vitro. In this study, we examined the effects of conventional and modified oocyte transport conditions on oocyte quality and subsequent embryonic development. Cumulus-oocyte complexes were collected from slaughterhouse-derived bovine ovaries and cultured in few drops of medium on plastic plates in a CO₂-incubator (Control), in plastic tubes containing medium (C-T) in air, or in tubes containing gellan gum and medium (MC-T) in air. C-T conditions reduced mitochondrial functionality (mitochondrial membrane potential and adenosine triphosphate), lipid content, and DNA methylation but increased mitochondrial DNA copy number and phosphorylated AMP-activated protein kinase (P-AMPK) levels compared to those in control oocytes. Furthermore, RNA sequencing analysis of blastocysts derived from these oocytes revealed that C-T conditions affected mitophagy- and AMPK-signaling-related genes. However, MC-T conditions attenuated these C-T-associated changes. In conclusion, conventional C-T conditions affect oocyte metabolism and alter embryo quality, whereas the use of gellan gum as a substrate ameliorates such adverse effects. The oocyte transportation system is inadequate for embryonic production and can induce epigenetic changes. Modifying these conditions with gellan gum is a useful counter-measure.