Semen is the fluid produced by male animals to carry sperm to the female ovum for fertilization. It contains components to provide nutrients to the sperm, keep them viable in the female reproductive tract and dilute the sperm to facilitate transfer to the female. The volume of semen produced varies among individuals and among species, and can be influenced by several factors.
On average, a human male can produce between 2 and 5 milliliters of semen.
In humans, the volume of semen is only 2 to 5 percent sperm. The rest of the volume is made up of fluids secreted by the epididymus, prostate gland and seminal vesicles. The epididymus contributes a small volume of fluid containing the electrolytes potassium and sodium and some nutrients for the sperm. The prostate gland contributes about 30 percent of the seminal fluid, with secretions including citric acid, minerals and enzymes. The seminal vesicles contribute about 60 percent of the seminal fluid, with secretions including sugar, amino acids, citric acid and prostaglandin hormones. The bulbourethral gland secretes a small amount of mucus for lubrication.
Human Semen Production
The average volume of semen produced at one time varies widely among individuals. The average human male produces a volume between 2 and 5 milliliters (0.06 to 0.17 U.S. fluid ounces). Semen volumes that are regularly lower than 1.5 milliliters (0.05 U.S. fluid ounces) are known as hypospermia, while semen volumes regularly higher than 5.5 milliliters (0.18 U.S. fluid ounces) are known as hyperspermia. Since semen is primarily made up of fluid secretions, the possible supply is inexhaustible.
Semen Volume in Other Species
Semen volume and semen concentration vary among species. To some extent, semen volume varies with body size. A mouse produces an average of 0.0015 milliliters (less than 0.01 teaspoon) at once, while the blue whale produces an estimated volume of 16,561 milliliters (17.5 quarts) of semen. Other animals produce more or less semen than would be expected for their body size. For example, pigs produce 200 milliliters (6.76 U.S. fluid ounces) of semen at once while the much larger bovine bull produces only 8 milliliters (0.27 U.S. fluid ounces) of semen, only slightly more than a man.
Factors That Influence Semen Volume
Across species, evolutionary history influences how much semen is produced. Monogamous animals have different fertilization needs than species where a female may mate with more than one male. In the second case, males need a way to give their genetic material an advantage, which may include increasing semen volume, a phenomena known as sperm competition. At the individual level, semen volume generally increases from young to mature males in livestock species. To some extent, semen volume is heritable, or encoded by genetics. Genetic defects such as cryptorchidism, or undescended testicle, also influence semen volume.