Immunization with a Streptococcus bovis vaccine administered by different routes against lactic acidosis in sheep

Streptococcus bovis is an important lactic acid bacterium in the rumen, whi ch contributes to the development of lactic acidosis. This study was design ed to test the efficacy of immunization with S. bovis primed either intramu scularly (i.m.) or intraperitoneally (i.p.) against lactic acidosis. Forty- five wethers were allocated to three treatment groups. Two groups were inje cted with a S. bovis vaccine by either the i.m. or i.p. route for primary i mmunization; both groups were further immunized by the same route(s) (oral and/or i.m.) for boosters. The third group was not immunized (control). Antibody concentrations were measured in saliva prior to and following anim als being fed a grain diet, and also in the rumen fluid, before the animals were suddenly introduced to a grain diet. The average antibody concentrati on in the animals of the i.m. group was higher than the i.p, group (P < 0.0 5). The antibody concentration in the rumen fluid of immunized sheep was hi gher than the control animals (P < 0.01). The difference in the rumen fluid antibody concentration between the i.m. and i.p. groups was not statistica lly significant (P > 0.05). In the i.m. group, there was a significantly gr eater feed intake, higher rumen pH, lower diarrhoea scores, and less increa se in blood packed cell volume following grain feeding than in the animals of the control group. The severity of diarrhoea and the increase of blood p acked cell volume in the animals of the i.p. group were also less than ill the animals of the control group. The results suggest that the risk of lact ic acidosis can be reduced by immunization against S. bovis, and that the i mmunization primed i.m. is more effective than the immunization primed i.p. (C) 2000 Harcourt Publishers Ltd.