Notice the clean dehorning job on this two-day-old calf. When using dehorning paste, apply it to calves when the animals are only one to two days old, says Vince Arreola, calf manager at Gore’s Inc. in Comanche, Texas. If you wait until the calves are a week old, they will be a little friskier and more likely to rub their heads against calf hutches, smearing the paste. Since the paste is a caustic acid, any smears can cause scarring beyond the intended application area.