Wagtendonk de-Leeuw et a., 1998, 2000, Bertolini et al., 2002b). Increased calf birth weights

are associated with an increase in dystocia and cesarean sections (Behboodi et al., 1995; Kruip

and den Daas, 1997; van Wagtendonk de-Leeuw et a., 1998, 2000) as well as perinatal mortality

(Behboodi et al., 1995; Schmidt et al., 1996; van Wagtendonk de-Leeuw et a., 1998, 2000). In

addition, calves that are produced from the transfer of in vitro produced embryos are associated

with a sex ratio skewed toward males (van Wagtendonk de-Leeuw et a., 1998, 2000), increase in

congenital malformations (Schmidt et al., 1996; van Wagtendonk de-Leeuw et a., 1998, 2000),

and altered organ development (McEvoy et al., 1998).

Potential causes

 It is well recognized that in vitro produced embryos differ markedly from their in vivo

derived counterparts in terms of ultrastructure (Crosier et al., 2001; Fair et al.., 2001; Rizos et al.,

2002), metabolism (Khurana and Niemann, 2000), and gene expression (Farin et al., 2004;

Lonergan et al., 2006). It is likely that many of these differences contribute to the problems

described above. At the ultrastructural level, embryos produced in vitro are associated with an

increase in cytoplasmic lipid content, alterations in the number and morphological characteristics

of mitochondria, and a reduced number of microvilli and intercellular contacts compared to

embryos produced in vivo (Crosier et al., 2001; Fair et al., 2001; Rizos et al., 2002). Khurana

and Niemann (2000) evaluated the metabolic activity of in vitro produced and in vivo derived

embryos and reported that in vitro produced blastocysts produced 2-fold more lactate than

blastocysts produced in vivo indicating a major difference in the metabolism of glucose between

the two groups of embryos. Several studies have also evaluated the effect of in vitro embryo

production of gene expression patterns in bovine blastocysts (Farin et al., 2004; Lonergan et al.,

2006). In general, these studies indicate that culture can increase the abundance of heat shock

protein 70 (Hsp70; Lazzari et al., 2002; Sagirkaya et al., 2006), increase levels of the pro-