The younger birds have a very very high survival rate. Most people lose the first one or two they attempt, but once they figure it out very rarely loose any more. It gets complicated when you attempt the older more mature birds, they are hard to do. I would never suggest a novice attempt a mature (or nearly mature) bird. I would be equally cautious w/ a vet who doesn't have experience w/ birds attempting a nearly mature bird. It is a skill I think is invaluable in some circumstances, and an AWESOME way to have multiple roos for whatever reason you would like w/o having to worry about noise, hen wear, fighting or human aggression. (at least as long as you don't want their breeding ability). If the boy are done young you can choose if they are to be pets or dinner. If you wait until they are older and have an emotional attatchment there is greater risk.
Caponizing - Page 20
I'm not sure how well this will show up but I figured I'd give it a shot anyway...
I posted on here a couple of years ago about when my dad and I used to caponize many chickens. I got some chickens again this spring and caponized an americauna and a buff orpington, both of which are doing well. It had been a long while but it came back pretty quickly.
It is of the utmost importance to take them off feed and water for at least 24 hours and preferably 36 hours prior to surgery. They'll be fine.
Attached is a scan of the instructions that came with a set of Beuoy tools that were made probably in the 1940s. In the second column it talks about taking them off feed and water. I hope it is readable. If anyone is interested, I can scan the rest of the pamphlet as well. It is very old.
My biggest tip would be not to, unless you are very skilled and / or don't mind losing him. Caponizing a grown (or mostly grown) roo, is exceedingly hard, both in technique and hard on the birds. I have seen it done successfully by one person on a couple of birds, but she is highly skilled, and she has even stopped caponizing older birds. I think she was most successful by doing each side a few weeks apart.
Yes it is called poulardizing. At least one caponizer was trying to poulardize her meat hens, but I don't remember her outcome. Hens only have one ovary on the left side if I remember right, the process involves removing the ova duct, and yes when successful they can no longer lay.