I have hen with one leg, she lost her leg as a chick. Bad break and infected at the joint. I took her to the vet and they were unable to save/splint the leg....too far gone (I got her at the farm store injured). They did amputate and she is almost a year old now. She does need alot of special care because her other remaining leg is somewhat deformed. I Have read on here that someone had an adult chicken that lost its leg and did fine as a one-legged and got around good on the remaining leg since it was formed and in good shape. I would NOT recommend amputating on your own, but instead take to vet. They cauterized and stitched my girl and she was also on pain meds and antibiotics afterward. If his roo has a break at the hip, they will probably take the whole leg and not leave a stump. Do a search on one-legged roos or chickens, I am sure someone on had one that got either attacked or something and lost its leg and did fine. Whatever needs to be done quick as infected will set in possibly, plus he is in pain.