Progesterone

What is Progesterone?

Progesterone is the "pregnancy hormone" — the key hormone for maintaining pregnancy in cattle. It is produced by the corpus luteum (CL), a temporary gland that forms on the ovary after ovulation. Progesterone prepares the uterus for embryo implantation, suppresses further ovulation, and maintains the uterine environment necessary for fetal development.

During the estrus cycle, progesterone follows a predictable pattern: low during estrus (allowing ovulation), rising after ovulation as the CL forms, peaking at mid-cycle (days 7–14), and declining if no pregnancy occurs (allowing a new cycle to begin). If the cow is pregnant, the embryo signals the CL to continue producing progesterone, maintaining pregnancy until the placenta takes over at ~day 150.

Progesterone testing is a powerful reproductive management tool. Milk progesterone tests can determine: whether a cow is cycling (normal pattern), whether she is pregnant (sustained high progesterone), whether she has cystic ovaries (persistently high progesterone without pregnancy), and the optimal time for breeding (low progesterone = estrus).

Progesterone-based protocols (CIDR, PRID) are widely used for estrus synchronization. These devices release progesterone to suppress ovulation, then are removed to induce synchronized estrus and timed AI. This allows breeding without heat detection.