The goal of this study was to assess the effect of Insulin like growth factor-1 (IGF-1) during in vitro culture on developmental competence of bovine embryos produced from heat-stressed oocytes. In this experiment, immatured oocytes were randomly assigned into two groups and matured at 38.5 or 41 ^°C for the first 12 hours of maturation followed by 12 hours at 38.5 ^°C. After in vitro maturation and fertilization, putative zygotes in each group were randomly allocated and cultured in the presence or absence of 100 ng/ml human recombinant (hr)-IGF-1. The results showed that cleavage rate was not affected by IGF-1 and heat stress, whereas blastocyst formation rate was significantly increased by IGF-1 in the presence and/or absence of heat stress. In addition, heat stress decreased blastocyst formation rate compared to the control
(38.5 ^°C without IGF-1) group. The number of trophectoderm cells, inner cell mass and total cell number were significantly increased by IGF-1 in the presence and/or absence of heat stress. In addition, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive nuclei were significantly decreased by IGF-1 in the presence and/or absence of heat stress. Results of this experiment demonstrated that IGF-1 can improve developmental competence of bovine embryos produced from heat-stressed oocytes. It seems that IGF-1 improve bovine embryo developmental competence via increasing of total cell number and decreasing of apoptosis.