Abstract
Evaluating bovine embryos for transfer and successful pregnancy has been challenging since the inception of embryo transfer in cattle over six decades ago. Despite thousands of publications on bovine embryo evaluation, no consensus or gold standard for assessing their developmental potential in vivo exists. This challenge extends beyond embryos to gametes. Various microscopic techniques [e.g., differential interference contrast, electron, fluorescent, time-lapse, and artificial intelligence (AI)-based microscopy and non-microscopic methodologies (including genomics, transcriptomics, epigenomics, proteomics, metabolomics, and nuclear magnetic resonance)] have been explored to supplant and surpass morphological evaluation. Many research tools that accurately determine embryo quality and viability are invasive, costly, labor-intensive, and time-consuming, making them impractical for field use. Future research should focus on creating field-friendly, simple benchtop tests based on existing findings, particularly from omics-based methodologies. Time-lapse monitoring and AI-based automated image analysis could provide accurate embryo evaluations. Further research is needed to develop economically viable options for field applications. Recent work has explored potential uses of nuclear magnetic resonance (NMR) imaging, label-free microscopy, especially holographic techniques like gradient light interference microscopy (GLIM), spatial light interference microscopy (SLIM) and multiphoton holographic microscopy in in vitro fertilization (IVF) labs. The ideal embryo evaluation tool should be accurate, objective, non-invasive, affordable, and simple for widespread adoption by facilities worldwide. It’s unlikely that transcriptomics, proteomics, or metabolomics can be directly used for field evaluations. However, biomarkers identified through these methods could guide the development of simple, affordable benchtop techniques for in-field use. Further research into advanced microscopy and AI-based automated image processing may lead to affordable, widely adoptable methods. The next generation of microscopy, capable of providing objective markers for gamete and embryo quality, is on the horizon. My journey in embryo biology, and especially embryo evaluation, has not been linear. I started college, studying wildlife and fisheries biology. As an undergraduate, I was fortunate to meet Professor Gary B. Anderson at the University of California-Davis in the early 1970s. He was exploring this new field of embryo transfer in cattle. This meeting profoundly changed my life and career trajectory. I completed my MS degree studying twinning in beef cattle using embryo transfer. I went from California to study for a doctorate in physiology and biophysics exploring bovine IVF at Colorado State University under Professor George E. Seidel, Jr. These two great scientists, mentors, and dear friends provided the foundation for my career of over 40 years studying embryo biology in not only cattle but mice, rats, rabbits, swine, horses, sheep, goats, frogs, white-tailed deer and various other species. Great mentors have a profound and lasting impact on their students. I am an example of having had great support and collaborations with many mentors throughout my career.