The present study was designed to investigate the efficacy of control of
lactic acidosis by immunisation against
lactic acid-producing bacteria, Streptococcus bovis and Lactobacillus. Ten steers were allocated to two treatment groups. One group was immunised with a
vaccine containing S. bovis (strain Sb-5) and Lactobacillus (LB-27) cells, and the other was a non-immunised control group. The
vaccine, using Freund's complete adjuvant for primary immunisation and Freund's incomplete adjuvant for boosters, was administered intramuscularly. After primary immunisation, boosters were given at 2 to 4 week intervals. Both anti- S. bovis and anti- Lactobacillus
IgG levels in saliva increased significantly (P < 0.01) after the 1st booster which were lower (P < 0.05) than the
IgG levels after the 2nd and 3rd boosters, but were not significantly different (P > 0.05) from the
IgG levels prior to a grain challenge (after the 4th booster). There were positive correlations between the anti- S.bovis and anti- Lactobacillus
IgG in serum and saliva. Compared with the control group, steers in the immunised group had higher (P < 0.05) feed intakes, lower (P < 0.05) rumen concentrations of
lactate and lower numbers of S. bovis and Lactobacillus. Three of the control animals were withdrawn from the grain challenge due to their rumen pH persisting below 5.2, while only one animal in the immunised group was withdrawn. These results suggest that the risk of
lactic acidosis can be reduced by immunisation against S. bovis and Lactobacillus.