I always thought that during mating in dogs/horses/humans, the sperm does not come directly from the testes but a gland, maybe even the vas deferens(not sure exactly). It is then replenished from the testes, either when needed or after it is reabsorbed into the body, when it is no longer fresh so to speak.
I would definitely keep a newly neutered male away from any in season girls for a while just to be safe.
When OH had vasectomy, Dr told us three months.
ETA: Which makes me think, during a vasectomey, the Vas are cut and tied. So it has to be somewhere between the Vas and the penis. This means it is impossible for it to come from the testes directly during ejaculation.
This post has been edited by KaiserGSD: 03 May 2008 - 12:53 AM