Mass. Gen. Laws ch. 272 § 79B
Whoever shows or exhibits at any horse show or exhibition in the commonwealth a horse with its tail cut in either manner prohibited in section seventy-nine A shall be punished by a fine of not more than two hundred and fifty dollars; provided, that this section shall not apply to the showing or exhibiting at such a show or exhibition of a horse with its tail cut in either manner prohibited by section seventy-nine A, if the owner of such horse furnishes to the manager or other official having charge of the horse show or exhibition at which such horse is shown or exhibited an affidavit by the owner, in a form approved by the director of the division of animal health of the department of food and agriculture, that the tail of such horse was so cut in a state wherein such cutting was not then specifically prohibited by the laws thereof and while the horse was actually owned by a legal resident of such state. Said affidavit shall state the year of such cutting, the name of the state wherein the cutting was done, and the sex and age of the horse, shall describe the markings of the horse, if any, and shall be subject to inspection by any officer or agent mentioned in section eighty-four.
Mass. Gen. Laws ch. 272, § 79B