Average: 340 days (range 320-370)
Horse gestation averages 340 days (11 months) with a wide normal range of 320-370 days. Colts tend to gestate slightly longer than fillies. Mares are seasonal breeders — peak fertility in spring/summer when day length increases. Pregnancy diagnosis: ultrasound at 14-16 days, rectal palpation at 18+ days, blood test at 45+ days. Most foalings occur at night (80% between 10 PM and 2 AM). Signs of impending foaling: waxing of teats (1-4 days before), relaxed vulva, dropped belly, restlessness. Stage 1 labor: 1-4 hours of sweating/pawing. Stage 2 (delivery): 15-30 minutes. Stage 3 (placenta): should pass within 3 hours. A retained placenta is a veterinary emergency.