The younger the bird is when caponized, the less likely he will crow as an adult. For me, the ideal age to caponize is between six and eight weeks of age. I've caponized birds that were a year old, and some stopped crowing within a week. Others that same age infrequently crowed after being caponized but lost interest in the hens, and some crowed and chased the hens acting like they still had all their man parts. All of their combs and wattles got lighter in color and shrank, and they were less active and started to put on weight, but some never un-learned rooster behaviors, like crowing.
If you're planning to caponize older birds, watch the comb and wattles during the procedure. A blue comb will signal the bird is distressed. One can remove the right testicle and wait a week to allow the bird to recover fully before attempting the left side. I know this is time-consuming, but if you are caponizing a rooster that's a pet, this is one way to reduce the risk to the bird.
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