When the mare is in estrus (heat), which usually occurs every 21-24 days during the breeding season, she is receptive to mating. The stallion mounts the mare and inserts his penis into her vagina, releasing semen that contains sperm. The mare's reproductive tract consists of the ovaries, fallopian tubes, uterus, cervix, and vagina.
After mating, the sperm travel through the mare's reproductive tract, and if one of them successfully fertilizes an egg released from her ovaries, pregnancy begins. The gestation period of a horse is approximately 11 months (340 days on average).
During pregnancy, the developing embryo or fetus receives nourishment from the mare through the placenta, which forms in the uterus. As the fetus grows, its organs and body systems develop, and it eventually assumes the shape and characteristics of a foal.
Toward the end of the pregnancy, the mare's udder begins to enlarge, and she starts producing milk in preparation for nursing her foal. When the time comes for birth, the mare's water bag ruptures and labor commences. The foal is usually born headfirst and the umbilical cord is severed once the foal is out.
After birth, the foal relies on its mother for food and care. The mare nurses her foal frequently, providing it with colostrum (the first milk produced after giving birth) and then transitions to regular milk. The foal also starts to explore its surroundings, gradually gaining strength and independence.
Horses typically reach sexual maturity between the ages of 2 and 3 years, although some breeds may mature earlier or later. Successful breeding requires careful management, including monitoring the mare's estrous cycle and ensuring appropriate timing for mating.