Estrus hormone is primarily estrogen because:

• A. Progesterone
• B. Testosterone
• C. Luteinizing hormone
• D. Estrogen

Answer: (D)

Estrus is driven by estrogen, the hormone produced by the growing ovarian follicles. As estrogen rises toward estrus, it makes the female receptive to mating and produces the physiological and behavioral signs of heat. It also causes changes in the reproductive tract, like thickening of the vaginal epithelium and alterations in cervical mucus, which support mating and potential fertilization. Progesterone rises after ovulation and supports pregnancy, not heat; it tends to suppress estrus. Testosterone is not the primary driver in females, and while luteinizing hormone is essential for ovulation, it is not the signal that creates estrus behavior. So the hormone most closely linked to the estrus phase is estrogen.