Granulocyte-macrophage colony-stimulating factor promotes development of in vitro produced bovine embryos

The objective was to determine whether granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates development of bovine embryos. In each experiment, oocytes were fertilized in vitro, GM-CSF was added to embryo culture medium at 8-10 h or 5 days after insemination, and development was monitored as the proportion of oocytes that formed blastocysts. Addition of recombinant bovine GM-CSF to serum-free medium at 8-10 h after insemination increased the percentage of oocytes that formed blastocysts (7.2% and 15.2% for control and GM-CSF, respectively). GM-CSF did not affect cleavage rate. Rather, the effect of GM-CSF seems to be exerted after Day 5 after insemination, as indicated by the following findings: 1) GM-CSF did not alter embryo cell number at Day 5 after insemination; 2) administration of GM-CSF at Day 5 increased the proportion of oocytes that developed to the blastocyst stage (6.7%, 13.0%, and 22.4% for control and 1 and 10 ng/ml GM-CSF, respectively); and 3) addition of serum at Day 5 increased development but prevented a further increase due to addition of GM-CSF at 10 h after insemination. Blastocysts from GM-CSF-treated cultures tended to be at earlier stages of morphological development (i.e., fewer blastocysts expanded at Day 7 and fewer were hatching or hatched at Day 9 after insemination). GM-CSF may play a role in the early development of bovine embryos and might be a useful molecule for increasing blastocyst production rates in serum-free culture systems.