A common question asked by many breeders is whether the volume of semen deposited into the mare affects fertility. When a mare and a stallion mate naturally the entire ejaculate is deposited into the mare. This volume is usually 50 ml or more and includes several billion sperm. However, when breeding mares using artificial insemination, good fertility can be achieved with as little as 1/2 ml of semen. I have been telling breeders for years that the volume of the ejaculate is not important as long as the stallion is producing good sperm numbers. For example, a stallion can produce 8 billion sperm with 80 ml of semen at a concentration of 100 million sperm/ml or 20 ml of semen at a concentration of 400 million sperm/ml. Volume of the ejaculate and concentration are inversely related (i.e. if volume goes up then concentration goes down).
