[Trial, in a contaminated environment, of an attenuated lyophilized vaccine against S. abortus ovis abortion in sheep].

Merinos ewe-lambs from Arles formed part of a transhumant flock in which S. abortus ovis infection was enzootic. A lyophilized living vaccine was prepared from an attenuated mutant strain of Salmonella abortus ovis. About one third out of 450 ewe-lambs of the same flock received one subcutaneous injection of vaccine 1 to 3 months before fecundation; the other ewe-lambs were used as controls. No modification of behaviour was observed after vaccination. Three months later, serological post-vaccinal "H" agglutinins tested by a microtechnique could still be detected. According to observations during the lambing period, 25 (18.8%) out of the 133 vaccinated ewes and 55 (20.2%) out of the 272 controls were non-pregnant, 6 (4.5%) and 33 (12.9%) of each group lambed abnormally (P less than 0.02), and respectively 4 and 15 ewes excreted wild strains of S. abortus ovis. These results suggested the favourable effect of vaccination in an abortive environment caused by S. abortus ovis.