Experimental Brucella ovis infection in pregnant ewes

Forty yearling Brucella-free ewes were inoculated with Brucella ovis by the conjunctival route in mid or late first pregnancy. Only a few ewes excrete d B ovis during pregnancy and gave birth to stillborn lambs, but most of th em excreted the organism at lambing or during lactation. One of the 11 lamb s which were born alive but died before they were weaned was found to be in fected postmortem. In contrast, none of the 46 surviving lambs which were r eared in isolation until adulthood, was found to be infected. At weaning, t he 40 ewes were mated again with five Brucella-free rams. Although many of the ewes excreted B ovis, none of the rams was found to be infected when ne cropsied after mating. Most of the ewes that became pregnant, all having ex creted B ovis during their first pregnancy, cleared the infection during th e second pregnancy. However, three remained persistently infected and excre ted B ovis in their milk throughout the second lactation. None of the lambs born to these three ewes was found to be infected when necropsied at weani ng.