CHAPTER 4
 INTERACTION BETWEEN SEASON AND CULTURE WITH INSULIN-LIKE
 GROWTH FACTOR-1 ON SURVIVAL OF IN-VITRO PRODUCED EMBRYOS
 FOLLOWING TRANSFER TO LACTATING DAIRY COWS

 Introduction

 Exposure to heat stress reduces fertility in lactating dairy cows (Badinga et al.,

1985; Lopez-Gatius, 2003). While early embryonic development is very sensitive to the

deleterious effects of heat stress, embryos become more resistant as development

progresses (Ealy et al., 1993; Edwards and Hansen, 1997). Thus, embryo transfer can be

used to bypass the period during which the embryo is most sensitive to heat stress and

improve fertility as compared to artificial insemination (Putney et al., 1989; Ambrose et

al., 1999; Drost et al., 1999; Al-Katanani et al., 2002). There does remain, however,

some detrimental effects of heat stress on pregnancy rates in embryo transfer recipients

(Vasconcelos et al., 2006; Galvao et al., 2006).

 One strategy to increase pregnancy success for transfer of in vitro produced

embryos is to alter embryo culture conditions to improve post-transfer viability of

embryos. Addition of IGF-1 to culture medium can increase development of bovine

embryos to the blastocyst stage (Palma et al., 1997; Prelle et al., 2001; Byrne et al.,

2002b; Moreira et al., 2002b; Block et al., 2003; Sirisathien et al., 2003b), increase

blastocyst cell number (Byrne et al., 2002b; Moreira et al., 2002b; Sirisathien et al.,

2003b) and reduce the proportion of blastomeres that are apoptotic (Byrne et al., 2002b;

Sirisathien and Brackett, 2003). Treatment of bovine preimplantation embryos with IGF-

1 also improves resistance to heat shock by reducing effects of elevated temperature on

blastomere apoptosis and development to the blastocyst stage (Jousan and Hansen, 2004,

2006).