Docking in sheep is done at the age of

Docking in sheep is done at the age of 7 - 14 days.
Docking is the intentional removal of part of an animal's tail or, sometimes, ears. The term cropping is more commonly used in the cropping of ears or tails.
Tail docking is performed in sheep to reduce the incidence of blowfly strikes that may result from urine and faecal staining of the perineum. Docking also makes it easier to view a grown ewe's udders to detect potential problems.