The basis of this hypothesis is that similar actions are caused by bST (Bilby et al., 2006) and the

supposition that these bST effects are mediated by IGF-1. Actions of IGF-1 on concepts length

and IFN-T secretion could enhance the capacity of embryos to block luteolysis and thereby

promote embryonic survival. The final question to be addressed in this thesis is whether effects

of IGF-1 on embryo survival are a general effect of IGF-1 or one specific to heat stress. Since

IGF-1 treatment in vitro can reduce the deleterious effects of heat shock on apoptosis and

embryo development (Jousan and Hansen, 2004; Jousan and Hansen, 2006), and since the

experiment by Block and others (2003) showing an effect of IGF-1 on post-transfer survival was

conducted in the summer, it is possible that actions of IGF-1 on embryo survival are the result of

a thermoprotective effect of IGF-1. If so, one would not see beneficial effects of IGF-1 on

embryo survival for recipients receiving embryos during cool periods.

 These questions form the basis for this dissertation. Subsequent chapters will address each

of these in order and the General Discussion in Chapter 5 will provide an overview of findings

and an updated perspective of how IGF-1 affects embryo physiology to affect post-transfer

survival.