PASSIVE-IMMUNIZATION OF NEONATAL LAMBS VIA COLOSTRUM AND MILK OF EWESPREVIOUSLY IMMUNIZED WITH LIVE ATTENUATED SALMONELLA-TYPHIMURIUM PROTECTS NEONATAL LAMBS FROM EXPERIMENTAL SALMONELLOSIS

Lambs sucking non-immunised ewes or ewes immunised 4-5 weeks before la mbing with live attenuated, aromatic-dependent (aroA) Salmonella typhi murium (strain CS 332) were challenged orally at either 2, 4 or 7 days of age with virulent S. typhimurium (strain CS 94) at doses ranging f rom 10(9) to 10(13) colony forming units. No lambs displayed signs of clinical salmonellosis and all survived challenge but those sucking im munised ewes had organisms of the challenge strain in their faeces for much shorter periods of time than lambs of the control ewes. High tit res of specific antibodies were measured in colostrum and milk of immu nised ewes in comparison with very low titres measured in samples from control ewes; these differences were reflected by the titres of antib odies in the sera of corresponding lambs. At 2 days after lambing, the major antibody isotype in the colostrum of immunised ewes and sera of their lambs was IgM whereas at 7 days IgG1 was the predominant isotyp e. While it was clear that vaccination of pregnant ewes with the live attenuated vaccination conferred protection against experimentally-ind uced salmonellosis in their lambs, considerable protection was observe d in control lambs in spite of there being very low titres of antibodi es in the mammary secretion of their darns. The latter observation cou ld be related to the presence of contain non-antibody potent bacterici dal factors previously described in colostrum and milk. (C) 1998 Publi shed by Elsevier Science Ltd. All rights reserved.