Which of the following best describes a dog estrus duration of 4-21 days with mean 9 days?

• A. 4-21 Days (Mean 9 Days)
• B. 7-28 Days (Mean 11 Days)
• C. 15-30 Days
• D. 1-5 Days

Answer: (A)

The key idea is the duration of the estrus phase in the bitch, which is the period of sexual receptivity. In dogs, estrus typically lasts about 9 days on average, with a wide possible range from roughly 4 to 21 days. The description that matches this well is 4-21 days with a mean of 9 days, because it reflects both the typical length of the phase and the common average. The other ranges either suggest a shorter or longer window than is normally observed for estrus, making them less accurate descriptions of this stage. In practice, recognizing the signs of estrus—standing heat, vulvar swelling, and vaginal discharge—occurs within that 9-day average window, guiding breeding timing.