gene is located at the Q region of the mouse major histocompatibility complex (Warner et al., 1987; Warner et al., 1991). Fair and colleagues (2004) have investigated expression of major histocompatibility complex class I transcripts in pre-implantation bovine embryos and reported that embryos that cleaved by 28 hrs post-insemination had an increased relative abundance of class I major histocompatibility complex transcripts compared to embryos that cleaved after 36 hrs. These results suggest that cattle may have a gene with a similar function to the mouseped gene and could be used as a marker for embryo selection. However, further investigation is required to identify the specific gene and its sequence. Measurement of metabolic activity is another potential strategy to select embryos prior to transfer (Gardner and Lane, 1997; Donnay et al., 1999). In particular the measurement of glucose uptake has been correlated with developmental capacity after transfer. Renard and colleagues (1980) were the first to report an effect of glucose uptake on subsequent post-transfer survival. A retrospective analysis indicated that the glucose uptake of day 10 in vivo produced bovine blastocysts was positively correlated with survival following transfer. A correlation between glucose uptake and embryo survival has also been reported for murine (Gardner and Leese, 1987) and human (Gardner et al., 2001) embryos. In addition to glucose, recent research using a nanorespirometer indicates that embryo respiration may also be an indicator of embryo viability (Lopes et al., 2007). However, further research with more transfers is needed to confirm these results. The use of proteomics could also provide new insights into novel markers which are important for embryo survival after transfer and that can be measured readily in embryo culture medium (Katz-Jaffe et al., 2006). In humans, a marker associated with pregnancy establishment has been identified. Embryos which secrete the soluble form of human leukocyte antigen-G