The slaves were bought young, and the new owners could decide how they should be.
If they were to work in coal mines or as a hooker, it would be better to blind them. If they were to carry heavy loads, pulling wagons for example, sometimes it was better to burst their eardrums so they would not be startled by noises.
If they were to work in the house of the noble families some preferred to castrate them so as not to take risks, others, on the other hand, chose the most gifted to have fun with their cocks. What was more common was to have their tongues cut off so they would not gossip, complain, or moan. It was also common to extend their anus, so that they could be penetrated without effort.
The sellers who did the interventions often ruin the animal, crippled or killed the creatures during the amputations.
The preparers lost many of them by hemorrhage or infection. But it was worth trying, the pieces valued a lot for already coming prepared.
The most important skill for surgeons was to know for what kind of slave the creature had more talent, more vocation or genetics. Children born from very large and strong slaves, the most stupid or revolted were separated for the heaviest jobs, the most gifted for the houses of meretrício.
These professionals were valued, the most skillful earned well, cared for the nobles, the citizens or the soldiers. The most unskilled professionals took care of horses, pigs, dogs or slaves, they made no difference.