When the governor has requested through the United States secretary of agriculture and accepted the cooperation of the United States department of agriculture, for the purpose of controlling or eradicating any contagious, infectious or communicable disease that may exist among any of the animals of this state, and when the said United States department of agriculture, through its duly authorized officers, agents or employees, shall be thus engaged, each of such officers, agents or employees shall possess the full power and authority of a state veterinarian under and by virtue of this chapter, and the rules and regulations of the state division, but shall not be entitled to claim reimbursement from the state for services he may perform unless a mutual agreement exists for cooperative employment and joint payment.