Bovine embryo freezability is closely linked with quality and differs between cow breeds (Visintin JA et al., 2002 Theriogenology 57, 345–359). Dark embryos have a bad freezability, resulting in low pregnancy rates (Hill BR and Kuehner LF, 1998 Theriogenology 49, 168). Excessive accumulation of lipid droplets in dark embryos is suggested to be the cause of this inferior embryo quality and in turn may be influenced by the biochemical composition of the embryonic environment. In a field trial we studied the relationship between donor breed (Holstein Friesian dairy cows v. Belgian Blue beef cows), donor serum total cholesterol and triglyceride concentration, embryo quality and embryo color. The preliminary results are presented. Blood was drawn from Holstein Friesian (HF) (n = 74) and Belgian Blue cows (BB) (n = 55) prior to embryo flushing on Day 7 after superovulation and subsequent insemination. Serum was analyzed for total cholesterol and triglycerides using commercial photometric assays. Embryos were scored individually by the same operator for quality (excellent to bad: score 1 to 4) and for color: light (L), medium (M) or dark (D) using a binocular stereomicroscope (40X). Student’s t-test, chi-square test and Spearman correlations were used when appropriate. Holstein Friesian cows yielded significantly more embryos (± SEM) per flushing than did BB (6.0 ± 0.59 v. 4.2 ± 0.44) (P < 0.05). However, significantly more HF embryos were classified as dark compared to the BB embryos (L, M, D: 39.4%, 43.8% and 16.8% v. 80.5%, 19.5% and 0% of the HF and BB embryos, respectively) (P < 0.05). Significantly more BB embryos showed an excellent morphological quality (55.0% of BB embryos compared to 28.4% of HF embryos) (P < 0.05). The serum concentrations (± SEM) of total cholesterol (148 ± 5.9 mg dL^-1 v. 106 ± 4.1 mg dL^-1) were significantly higher and the serum concentrations of triglycerides (19.6 ± 0.71 mg dL^-1 v. 28.4 ± 3.34 mg dL^-1) were significantly lower in HF compared to BB (P < 0.05). Within the HF breed, there was a significant positive correlation between donor blood total cholesterol and the color of each embryo (r = 0.545) and a negative correlation between serum triglycerides and embryo color (r = -0.484) (P < 0.05). In our study, embryo quality and color as well as serum total cholesterol and triglyceride concentrations are clearly influenced by donor breed. Within the HF breed, darker embryos originate from donors with higher serum total cholesterol and lower serum triglyceride levels. These preliminary data suggest that factors influencing total cholesterol and triglyceride concentrations in the donor blood (e.g. breed, milk yield, nutrition) may influence embryo color and thus embryo lipid content, freezability and subsequent pregnancy rate.