Heat shock on bovine embryos from day 2.5–3 selects the most competent for progression to the blastocyst stage

Abstract

Heat shock can impair embryo formation, while growth factors, such as colony-stimulating factor 2 (CSF2), modulate embryonic development. This study evaluated the effect of heat shock between days 2.5 and 3, as well as the impact of CSF2 at day 5 on bovine embryos cultured in a serum-free in vitro medium. The focus was on blastocyst development, the number of blastomeres, DNA fragmentation (TUNEL-positive cells), and mitochondrial activity. Heat shock reduced the proportion of cleaved embryos that developed into blastocysts (P = 0.0603). The resultant blastocysts exhibited a reduced number and proportion of TUNEL-positive cells in the trophectoderm (P = 0.0270 and P = 0.0240, respectively) and in the entire embryo (P = 0.0029 and P = 0.0031, respectively). Additionally, mitochondrial activity was lower in blastocysts derived from heat-shocked embryos (P = 0.0150) and further reduced in embryos exposed to both heat shock and CSF2 (P = 0.0415). In conclusion, the exposure of cleaved embryos to heat shock reduced their development to the blastocyst stage. However, the resulting blastocysts showed decreased DNA fragmentation and mitochondrial activity.