I don't actually castrate ram lambs, I band the sack leaving the testies in the body. This leave the testoserone producing organs and should help promote lean growth. I don't find these guys become aggresive until they are around 8 months and few make it past that anyhow. To properly castrate use a band as soon as you can pull both testies into the scrotem and get a band securly above them. Its more a weight thing and there will be breed differences, but I haven't done all that many to say exactly.