The recommendation is to dock the tail immediately below the third palpable joint or to the tip of the vulva in ewes.
This tail length allows the sheep to lift its tail and channel urine and faeces away from the breech area. It also reduces the risk of cancers from exposure of soft tissue to the sun.
Download the Kondinin Group article on correct tail length below.
The 'Te Pari Patesco' docking iron cauterises and removes the tail. It is similar to conventional docking irons, but works on a rotating anvil system that extends the skin on the woolly side of the tail, leaving a bare area on the tip of tail. Some producers have found this reduces the amount of dag forming around the tail and breech.