I always seem to have problems with callous bumps bothering my ducks. I do spray my ducks with Vetericyn as a weekly maintenance and use triple antibiotic cream after. This has seemed to reduce the issue. The soaking (especially if you have more then one duck limping) can be tedious, but it does really help. I then spray with Vetericyn and use the antibiotic cream or Iodine. If the callous is bigger, I carefully use human callous remover several times until it hardens up, then I can pull out the core. After pulling out the core, I continue the soaking, vetericyn, antibiotic cream daily until it hardens over. I have one duck where the callous is completely gone, but if you watch carefully, he still tends to limp ever so slightly.