Mass. Gen. Laws ch. 272 § 79A
Whoever cuts the bone of the tail of a horse for the purpose of docking the tail, or whoever causes or knowingly permits the same to be done upon premises of which he is the owner, lessee, proprietor or user, or whoever assists in or is present at such cutting, shall be punished by imprisonment for not more than one year or by a fine of not less than one hundred nor more than three hundred dollars; and whoever cuts the muscles or tendons of the tail of a horse for the purpose of setting up the tail, or whoever causes or knowingly permits the same to be done upon premises of which he is the owner, lessee, proprietor or user, or whoever assists in or is present at such cutting, shall be punished by a fine of not more than two hundred and fifty dollars. If a horse is found with the bone of its tail cut as aforesaid or with the muscles or tendons of its tail cut as aforesaid, and with the wound resulting from such cutting unhealed, upon the premises or in the charge and custody of any person, such fact shall be prima facie evidence of a violation of this section by the owner or user of such premises or the person having such charge or custody, respectively.
Mass. Gen. Laws ch. 272, § 79A