conversely, when there is an absence of newborns, excessive maternal behavior is due to the increased progesterone levels resulting from estrus in un-bred bitches, followed by an immediate and sharp decline in the progesterone levels.

This is all lower case. Can you fix that?
Conversely, when there is an absence of newborns, excessive maternal behavior is due to the increased progesterone levels resulting from estrus in un-bred bitches, followed by an immediate and sharp decline in the progesterone levels.