Ductus Deferens

An older term (still widely in use) for the ductus deferens is vas deferens (from L. vasa = "vessel," + deferens, the present participle of defero = "to carry away"). Hence the common name for the surgical operation that severs or ligates this organ before it enters the urethra: "vasectomy." To be up to date with modern terminology we really ought to call this a "deferenectomy," a much clumsier word.

In humans vasectomies are done for purposes of sterilization. They aren't done too often in animals, as the cost and trouble is substantially the same as a straight-out castration. Furthermore, vasectomy doesn't affect the activity of the interstitial cells: they still make testosterone, so sexual drive and testosterone-influenced behaviors and characteristics are unaffected. For psychological reasons simple castration isn't usually an option offered to human patients except as an extreme measure in some cases of cancer.

But the small animal clinic's client usually brings a male dog to be castrated because of unwanted behavior, such as roaming and aggressiveness. These are usually reduced when the supply of testosterone is cut off (ha, ha!). A vasectomized dog will show the same aggressive behavior and tendency to roam and mate as an untouched one, even though he's shooting blanks.

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