We can't exactly use the movies as a definitive source because Peter Jackson made plenty of changes, to help the plot along. I don't think audiences would have liked graphic scenes of Orc copulation. [img]smilies/biggrin.gif[/img]

The Uruk-hai originally came from Mordor, but Saruman could have still bred some of them with Men or other, smaller Orcs. I think that Orcs reproduce like any other species, but the raising of the offspring would be reminiscent of the animal world. The animal mother stays with her children just long enough to teach them how to survive. I think an Orc mother would do the same thing. Once the "children" could fend for themselves, or were grown enough to find their own resources, they were kicked out of the "lair." That seems like a much more logical means of reproduction, rather than mud-filled spawning pits, like the ones that Peter Jackson put in his movie.