2002b; Block et al., 2003) and have increased cell numbers (Byrne et al., 2002b; Moreira

et al., 2002b; Sirisathien et al., 2003b) they may be able to block this increase in PGF

secretion by producing more IFN-T. Conversely, during cool periods when PGF secretion

is less likely to be altered, this effect of IGF-1 may not be beneficial.

 Overall pregnancy loss between day 21 and term in the present study was 70.2%

(80/114). A total of 50.2% (96/182) of pregnancies were lost between day 21 and day 30

of gestation; this period is thus a major source of pregnancy loss. It is likely that the day

21 pregnancy rate is an overestimate and therefore should be interpreted carefully. Other

factors such as recipient asynchrony, extended estrous cycles (> 21 days), luteal cysts and

subclinical uterine infections could have contributed to elevated plasma progesterone. It

is also important to note, however, that similar pregnancy losses between day 21-22 and

day 42-52 have been reported in lactating dairy cows following artificial insemination

and embryo transfer (Ambrose et al., 1999; Drost et al., 1999; Chebel et al., 2004).

 Interestingly, day 21 to day 30 of gestation was also the time during which IGF-1

had a major effect on embryo survival. The beneficial effect of IGF-1 on embryo

survival during this time period was only evident during the hot season. While there was

no difference in pregnancy loss between IGF-1 and control embryos from day 21 to day

30 in the cool season (57.1% vs. 50.0%, respectively), there was significantly less

pregnancy loss from day 21 to day 30 for IGF-lembryos compared to controls during the

hot season (37.3% vs. 70.7%, respectively). This result suggests that IGF-1 treatment

from day 1-7 after insemination is affecting events after the time of maternal recognition

of pregnancy and during the peri-attachment period of gestation. These events could

include overall growth of the embryo or the program of gene expression. One possibility