[Experimental infection of sheep with Salmonella abortus ovis: effect of the gestational stage].

An inoculum of 1 X 10(10) S. abortus ovis was administered subcutaneously to non-pregnant Pre-Alpine X Merino ewes (group 1 : 37 days before fecundation) and to pregnant ewes (groups 2 and 3: 33 or 89 days after fecundation). The proportion of abortions to gestations in each group was 0/9, 1/9, 8/10 respectively. In group 2, there was only one abortion which occurred 64 days after inoculation. In group 3, the average time between inoculation and abortion was 19 days; three ewes died of an S. abortus ovis septicaemia after abortion and placental retention. No S. abortus ovis was isolated from the ewes' rectal swabs or from the carcasses 3 to 9 months after inoculation or abortion. The kinetics of responses in antibodies fixing the complement or agglutinating the O or H antigens were comparable in all groups; after reaching a maximum in about one week the serological titers decreased rapidly. The clinical and bacteriological results show a relationship exists between the physiological state of the ewes' genital organs and the probability of experimentally obtaining an S. abortus ovis abortive infection.