Duration of Heat (Estrus) in Mare

Duration of heat (estrus) in mare is:

Correct Answer: 6 days

The duration of estrus (heat period) in the mare is approximately 6 days — the longest estrus duration among all common domestic animals.

Reproductive Data for Mare

• Estrous cycle: 21 days
• Estrus duration: 6 days ✔
• Ovulation: occurs 1–2 days before end of estrus (day 4–5 of a 6-day heat)
• Long-day breeder (seasonal polyestrous)
• Uterus: T-shaped, bipartite type
• Gestation period: 341 days (≈ 11 months + 11 days)

AI Timing in Mare

Because the mare has a 6-day heat with ovulation near the end, AI is recommended every 2 days during estrus — or once after confirmed ovulation by ultrasound.

Why Other Options Are Wrong

• 9 days → estrus duration of the bitch, not the mare.
• 2 days and 4 days → do not correspond to any standard domestic animal.