The Oestrous Cycle The cows reproductive cycle is termed the oestrous cycle and consists of several phases including a luteal phase (after ovulation the corpus luteum is formed) and a follicular phase (luteolysis and ovulation)1. A healthy cow typically has a cycle between 18-25 days long, during which the progesterone levels increase and decrease systematically. What Is Progesterone? Progesterone is a steroid hormone and is produced by the corpus luteum in the ovary after ovulation. If a cow falls pregnant,…