The invention relates to the field of veterinary medicine and can be used for the prophylaxis of bovine leukosis. The invention expands the range of agents available to serve the claimed purpose and gives animals life-long resistance to the leukosis virus. The invention is directed toward solving the problem of broadening the spectrum of prophylactic drugs and developing new approaches to the problem of preventing bovine leukosis, which make it possible to provide animals with life-long resistance to infection by leukosis. The technical result lies in the creation of an agent and a method for the prophylaxis of bovine leukosis, which make it possible to provide a targeted immune response effectively and at little cost by activating cell-mediated immunity to the bovine leukosis virus by increasing the number of killer cells. An agent for the prophylaxis of bovine leukosis contains a water-soluble protein fraction with a molecular mass of 18-20 kDa, isolated from Mycobacterium tuberculosis degradation products and characterized by the presence of peaks at a wavelength of 214 nm in the ultraviolet region of the spectrum, phosphate-buffered saline, an aqueous solution of formic aldehyde, and an isotonic solution of sodium chloride. The proposed method consists in administering said agent to 1-9 day old calves in a single intramuscular dose of 4.0-6.0 ml per head.La invención se refiere en general al campo de la medicina veterinaria y puede usarse para la prevención de la leucemia bovina. La invención amplía la gama de medios de la aplicación reivindicada y proporciona resistencia de por vida a los animales contra el virus de la leucemia. El objetivo de la invención es resolver el problema de ampliar el rango de medicamentos preventivos y formar nuevos procedimientos para el problema de prevenir la leucemia bovina, que permite asegurar la resistencia de los animales durante toda la vida a la infección por leucemia. El resultado técnico consiste en el diseño de un remedio
