In mares, a granulosa cell tumor commonly arises from granulosa cells and often causes which behavioral change due to estrogen production?

• A. Estrogen
• B. Testosterone
• C. Progesterone
• D. Cortisol

Answer: (A)

Granulosa cell tumors in mares produce estrogen in excess. This rise in estrogen drives signs of estrus, so affected mares show persistent estrous behavior—being continually receptive to a stallion and displaying typical heat signs such as vulvar winking and other outward estrous behaviors—even outside the normal breeding cycle. The other hormones listed would lead to different effects: testosterone would cause male-typical behaviors, progesterone would promote diestrus-like quieting of estrous behavior, and cortisol is not tied to this ovarian tumor’s effects.