The Law (Animal Welfare (Care and Procedures) Regulations 2018) says: 

Docking cattle beasts’ tails 

1. A person must not dock the tail of a cattle beast. 
2. A person who fails to comply with this regulation commits an offence and is liable on conviction,—
   (a) in the case of an individual, to a fine not exceeding $3,000; or
   (b) in the case of a body corporate, to a fine not exceeding $15,000. 
3. A person has a defence to a prosecution for an offence against this regulation if the person was required to urgently dock the tail of the cattle beast in response to an accidental tail injury in order to prevent excessive bleeding or further injury to the cattle beast. 
4. A person has a defence to a prosecution for an offence against this regulation if—
   (a) the person was a veterinarian, or a veterinary student under the direct supervision of a veterinarian throughout the procedure; and
   (b) the person docked the tail of the cattle beast for therapeutic purposes; and
   (c) the cattle beast was given pain relief at the time of the procedure. 

What does this mean for you? 

It means if you need one of your cows’ tail (or part of tail) removed, you  MUST  call a veterinarian. It also means that you and the veterinarian need to document the removal, and to keep those records. When that cow eventually leaves the herd, you could be asked why she does not have a tail (and need to produce a tale!).