What Is Progesterone?
Progesterone is the hormone that indicates ovulation and helps maintain a pregnancy in dogs.
By testing progesterone levels, you are able to pinpoint the day of ovulation and plan matings that are more likely to result in success.
Hormones of a Bitches Cycle
Progesterone starts to rise just before ovulation, toward the last week of the heat cycle. It is well established that as soon as the progesterone levels are around 2 ng/mL, luteinising hormonepeaks and ovulation takes place when the progesterone levels are around 5–8 ng/mL. From this point, eggs require 48 hours to mature, and by that time the progesterone levels usually average 10 ng/mL or above.
The Ovarian Cycle of the Bitch
Estrogen levels are rising. The hormone of interest, progesterone, of the bitch is low, less than 2ng/ml. This is often reffered to as “baseline”.
As the bitch enters estrus, she approaches her fertile period and her progesterone level will rise above 2ng/ml. She will become increasingly attractive to the male and receptive to his advances. This slight rise is often called the initial rise, you will want to monitor her progesterone levels more closely now as she is about to ovulate.
Bitches are only fertile for a few short days during estrus, not the entire time they are in estrus.
Ovulation occurs when progesterone levels reach 5 ng/ml. Luteinizing hormone hormone (LH) is released from the pituitary, which triggers ovulation. Eggs are not ready to be fertilised until they mature (around 48 hours).
The timing of breeding must occur when the eggs are mature and ready to fertilise and viable semen is in the oviduct, estimating how long the semen is anticipated to survive in the reproductive tract.
After ovulation and breeding are completed, progesterone levels will continue to rise, typically to 40-50 ng/ml whether the bitch is bred, pregnant, or not. An elevated progesterone level only indicates that the corpus lutea in the ovaries can support a pregnancy, not that the bitch is pregnant.