A new fact sheet published by the University of Wisconsin Extension service provides the latest information on best practices for disbudding/dehorning dairy calves.
According to the fact sheet, "removing horns from dairy cattle is an important farm safety practice because it prevents injuries to people and cattle. Removal of the horn or horn bud is a painful procedure and can be minimized by disbudding/dehorning cattle at a young age with proper pain management. Ideally, disbudding/dehorning should occur prior to six weeks of age. After this age the horn bud attaches to the skull, and the procedure is much more invasive."
The resource states that hot iron disbudding is safe for calves up to six weeks of age, and includes step-by-step instructions for the procedure. Local anesthesia and non-steroidal anti-inflammatory drugs are highly recommended for every animal.
Caustic paste applied at less than three days of age is presented as an alternative option. Instructions for optimal caustic paste application are included as well.
The full document can be accessed here.