Procreation in any species borders on the miraculous. How else can one describe a phenomenon where two microscopic entities intersect, join forces, and grow into a living, breathing creature that, in the case of the horse, will weigh 1,000 pounds or more at maturity. Science, of course, does not deal in miracles. It involves itself in no-nonsense facts and observations that have unraveled some of life’s greatest mysteries. The matter of equine reproduction is a case in point. Science can take us step by step through the process from the time sperm meets egg until approximately 11 months later when the foal is born.

The placental membranes not only are a literal life support system for the growing fetus, but also provide clues after birth as to why problems occurred (if they did during pregnancy).

Photo: Barbara D. Livingston

Unfortunately, the "miracle" does not always occur. There are pitfalls all along the route and any one of them can terminate a pregnancy before it reaches term.

The estrous cycle of the mare has been explored in these pages in some detail in recent issues (see The Horse of December 1998), so we will begin our discussion of fetal development and foal growth at the climactic step in any given cycle–fertilization.

Fertilization occurs in the oviducts, also known as fallopian tubes. The sperm is deposited directly into the uterus by the stallion, or b