Studies in vitro have
indicated a relatively low requirement for glucose during the early stages of embryo development
(Thompson, 2000). An embryo’s ability to utilise glucose has, however, been
linked to its developmental competence (Lequarre et al., 1997; Krisher and Bavister,
1999), thus indicating glucose to be an important substrate, since pre-morula stage embryos
require an additional energy source to lactate and pyruvate in order to reach and develop past the blastocyst stage (Leese and Barton, 1984).
In conclusion, the present study demonstrated a close relationship between the stage of
embryo development and both plasma and luteal progesterone as early as day 5 post-oestrus.
This provides evidence that progesterone is fundamental to early embryo development and
survival in the dairy cow. It also substantiates previous work that the timing and rate of the
post-ovulatory progesterone rise is critical to early embryo development in cattle.