Post-transfer development and survival

 The transfer of bovine embryos produced in vitro is associated with an increased frequency

of abnormalities related to embryonic, fetal, placental and neonatal development. These

developmental errors include a wide range of phenotypes including increased rates of embryonic

mortality and abortions, production of large fetuses and calves, alterations in development of the

allantois, a sex ratio skewed toward males; increased proportion of calves with congenital

malformations, and increased neonatal abnormalities (Farin et al., 2001; Farin et al., 2006).

These abnormalities had been collectively termed large offspring syndrome, but recently have

been more appropriately renamed abnormal offspring syndrome (Farin et al., 2006).

 Regardless of whether embryos have been cryopreserved or not, bovine embryos produced

in vitro are associated with reduced embryo survival rates following transfer. Pregnancy rates

following the transfer of in vitro produced bovine embryos are reduced compared to those

obtained following the transfer of in vivo derived embryos (Hasler et al., 1995; Farin and Farin,

1995; Drost et al., 1999).

 In addition to problems with reduced pregnancy rates, embryos that survive to the fetal

period are more likely to be lost. While pregnancy loss after the first two months of gestation for

superovulated embryos is generally less than 5% (King et al., 1985; Hasler et al., 1987),

pregnancy loss after day 40 of gestation for in vitro produced embryos has ranged from 12% to

24% (Agca et al., 1998; Hasler, 2000; Block et al., 2003). In two studies in which abortion rate

was compared between cows that received an embryo derived in vivo or an in vitro produced

embryo, abortion rates were increased for cows that received bovine embryos produced in vitro

(Hasler et al., 1995; van Wagtendonk de-Leeuw et al., 2000).

 The increased fetal loss that characterizes pregnancies from embryos produced in vitro is

most likely related to the abnormal fetal and placental development of in vitro produced bovine