Mass. Gen. Laws ch. 129 § 44A
Any equine animal positive to a test approved by the United States Department of Agriculture for the detection of equine infectious anemia may be humanely destroyed; provided, that such destruction is observed by an agent of the division or of the United States department of agriculture, or may be so destroyed by a licensed veterinarian who shall report such destruction to the division, or may be sold or given under a permit from the division to an approved slaughter house or research facility, or, at the owner's option, may be retained under quarantine and held in isolation on the owner's premises; provided, however, that it may be pastured, ridden or driven on the owner's premises within a radius of two hundred yards of where it is stabled, provided, that no other horses are stabled or normally ridden or pastured within that area. Upon the discovery of one or more test positive animals within a quarter of a mile of where such animal is normally stabled, all such reactor animals shall be quarantined to screened stalls.
Mass. Gen. Laws ch. 129, § 44A