(a) Relative expression (mean ± SEM) of EGFR transcript in 8–16-cell embryos on day 3 cultured either singly or in groups without (D3S, D3G) or with EGF supplementation (D3SE, D3GE). (b) Relative expression (mean ± SEM) of EGFR transcript in morulae on day 5 cultured either singly or in groups without (D5S, D5G) or with EGF supplementation (D5SE, D5GE). (c) Relative expression (mean ± SEM) of EGFR transcript in blastocysts on day 7 cultured either singly or in groups without (D7S, D7G) or with EGF supplementation (D7SE, D7GE). Relative expression analyzed using real-time PCR with YWHAZ used to normalize each gene, and 4–8-cell embryos (D2) used as calibrators. a,b Different letters on bars indicate values that differ significantly (P < 0.05).