Castration, or the removal of the testicles, is carried out on the male pig which is not needed for breeding. If the blood vessel to the testicle is cut straight through, or pulled, heavy bleeding can occur. Bleeding is reduced by scraping the twisted blood vessel with a knife until it is cut through. Castrated animals are quieter and easy to handle. The castrated animal is fatter and produces meat which does not have a strong smell.
Male pigs (boars) can fight causing injury to one another. Castrated pigs are quieter and easier to handle. Castrating the pig makes it put on more fat and the meat does not have a strong piggy smell. Young pigs should be castrated at 2 to 3 weeks of age.
You will need someone to hold the piglet for castration. The pig should be held by the hind legs with its head down and its body should be firmly held between the handler's knees.
You will need a very sharp, clean knife, scalpel or razor blade. Remove the sow from the litter and if possible put her where she cannot see or hear them.
Put the piglets and their mother on clean bedding. Watch piglets for signs of infection in the wound for the next week. Infected castration wounds swell, piglets do not want to walk or are lame.
Source : Pashu Sakhi Handbook