The article by Tervit, Whittingham, and Rowson describes successful in vitro culture of sheep and cattle ova, which have historically shown limited development. The authors report that fertilized sheep and cattle ova can be cultured from the one-cell to eight-cell stages and further developed to morula and blastocyst stages. They used a modified Dulbecco’s phosphate-buffered salt solution (PBS) for sheep ova and TCM-199 for cattle ova, both supplemented with specific nutrients. Preliminary experiments identified a medium based on sheep oviduct fluid (SOF) that promoted optimal cleavage. The study also explored the impact of oxygen concentration on embryo development, finding that 5% oxygen was most conducive to normal development. The cultured embryos were transferred to synchronized recipients, and a high survival rate was observed, with viable conceptuses developed to stages comparable to non-cultured embryos. The results demonstrate that a combination of suitable medium and gas phase can support the in vitro development of sheep and cattle ova beyond the previously observed developmental block.The article by Tervit, Whittingham, and Rowson describes successful in vitro culture of sheep and cattle ova, which have historically shown limited development. The authors report that fertilized sheep and cattle ova can be cultured from the one-cell to eight-cell stages and further developed to morula and blastocyst stages. They used a modified Dulbecco’s phosphate-buffered salt solution (PBS) for sheep ova and TCM-199 for cattle ova, both supplemented with specific nutrients. Preliminary experiments identified a medium based on sheep oviduct fluid (SOF) that promoted optimal cleavage. The study also explored the impact of oxygen concentration on embryo development, finding that 5% oxygen was most conducive to normal development. The cultured embryos were transferred to synchronized recipients, and a high survival rate was observed, with viable conceptuses developed to stages comparable to non-cultured embryos. The results demonstrate that a combination of suitable medium and gas phase can support the in vitro development of sheep and cattle ova beyond the previously observed developmental block.