Um, Castration Is Legal?

I'm not quite sure how I missed this. Bobby Jindal, mayor of Louisiana (a name we should start hearing a lot more in the next few years), signed an interesting bill into law over the summer. Apparently, certain sex offenders can now be chemically or physically castrated as a part of their sentence. The bill says,

on a first conviction of aggravated rape, forcible rape, second degree sexual battery, aggravated incest, molestation of a juvenile when the victim is under the age of 13, or an aggravated crime against nature, the court may sentence the offender to undergo chemical castration. On a second conviction of the above listed crimes, the court is required to sentence the offender to undergo chemical castration.

Jindal explained the bill,

I want to send the message loud and clear – to the Supreme Court of the United States and beyond – make no mistake about it, if anyone wants to molest children and commit sexual assaults on kids they should not do so here in Louisiana. Here, we will do everything in our power to protect our children and we will not rest until justice is won and we have fully punished those who harm them.

I mean, thanks for protecting children. But castration? Is this the Middle Ages? How can this possibly be legal?