THE PATHOGENESIS OF EXPERIMENTAL BRUCELLOSIS IN VIRGIN HEIFERS WITH AND WITHOUT CONTINUOUS PROGESTERONE TREATMENT

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Abstract
SUMMARY: Daily injections of progesterone were given to six adult heifers. These, and six untreated but otherwise similar animals, were infected by a standard method with the virulent strain 544 of Brucella abortus. The pathogenesis of the disease, as measured by B. abortus counts in various tissues and organs, and associated histopathology, was found to be less progressive and milder than in the pregnant cow. In the non-gravid animals the counts of B. abortus in the various tissues were very low and the infection did not disseminate very widely in the body. The uteri remained free from infection. In addition, the lesions in the lymphoid tissue were milder than those found previously in similarly infected pregnant animals. Progesterone administration exerted a profound effect on the genital tract. Oestrous cycles ceased and follicles in the ovaries became atretic; the endometrial glands secreted a material which accumulated in the uterine lumen and a firm mucus seal developed in the cervix. Progesterone, however, exerted no effect on the pathogenesis of brucellosis. It is concluded that progesterone is unlikely to be responsible for the susceptibility of the pregnant cow to brucellosis.