Answer:
The development of a horse begins with the fertilization of the egg by the sperm. The fertilized egg, called a zygote, divides and grows into a ball of cells called a blastocyst. The blastocyst implants in the lining of the uterus and begins to develop into an embryo.
During the first few weeks of development, the embryo forms three layers of cells called the ectoderm, mesoderm, and endoderm. These layers will give rise to the different tissues and organs of the horse's body. The heart, blood vessels, and muscles develop from the mesoderm, while the skin and nervous system develop from the ectoderm. The digestive, respiratory, and urinary systems develop from the endoderm.
At about eight weeks of development, the embryo is called a fetus. The fetus continues to grow and develop, and at around 11 weeks, the first signs of the horse's hooves and tail can be seen. At this stage, the fetus is about the size of a large lemon.
During the last trimester of pregnancy, the fetus grows rapidly and the organs and tissues continue to develop and mature. The foal is born after an average gestation period of 11 months, and it is able to stand and walk within a few hours of birth. The foal will continue to grow and develop for several years, reaching its full size and maturity at around 5-7 years of age.