Immunisation of dairy heifers with a Staphylococcus aureus bacterin reduces infection level and somatic cell counts at time of calving

Use of a Staphylococcus aureus bacterin to prevent intramammary infections (IMI) in dairy heifers was evaluated. At 6 to 18 months of age, Holstein heifers were processed for vaccination and collection of mammary secretions. Fifty-three heifers were immunised with a commercial bacterin and 53 heifers served as unimmunised controls. The vaccine was a lysed culture of polyvalent S. aureus somatic antigens of 5 phage types in an aluminum hydroxide base. Two weeks after processing and at 6-month intervals until calving, vaccinates were processed for boosting. At 2-month intervals after trial initiation and through calving, mammary secretion samples were collected for bacteriological culture and somatic cell counts (SCC). Efficacy data showed that the percentage of heifers with S. aureus IMI at calving was lower in vaccinates (13.3%) compared with controls (34.0%); a reduction of 60.9%. The SCC in samples collected at calving from uninfected heifers for vaccinates and controls were 66,095 and 132,754/ml, and for infected heifers, SCC were 441,764 and 892,176/ml; reductions of approximately 50%. Likewise, average first lactation SCC were lower in vaccinates than controls (49,000 vs. 60,000/ml). The 305-day lactation milk yield for the first lactation demonstrated an 8.6% increase in vaccinates vs. controls (11,217 vs. 10,332 kg). In addition, the 305-day lactation kilograms of fat and protein were higher in vaccinates than controls (fat: 408.04 vs. 338.96 kg; protein: 329.77 vs. 315.23 kg). Evaluation of the number of days in milk for the first lactation demonstrated that vaccinates persisted 13 days longer than unvaccinated controls (349 vs. 336 days), and culling was reduced by one-third in vaccinates (16.9%: vaccinates, 24.5%: controls). Results demonstrated that administration of a commercial bacterin to breeding age and pregnant heifers reduced prevalence of S. aureus mastitis and SCC at calving, and increased first lactation performance.