Evaluation of the Efficacy of SCSP Vaccine Against Streptococcus uberis Mastitis in Dairy Cows

This study evaluated the efficacy of the Staphylococcus chromogenes surface-associated proteins (SCSP) vaccine against experimentally induced Streptococcus uberis mastitis in dairy cows. Sixty healthy pregnant Holstein dairy cows were randomized into SCSP-vaccinated (n = 30) and unvaccinated control (n = 30) groups. Cows in the SCSP group were given two subcutaneous vaccinations of SCSP vaccine with Emulsigen-D adjuvant at drying off (D0) and 21 days after drying off (D+21), whereas cows in the control group were injected subcutaneously with phosphate buffered saline (PBS, pH 7.5) with Emulsigen-D at similar time points. Clinical observation of cows for mastitis and other diseases, body temperature, vaccine injection site reaction, bacteriological culture of mammary secretion, and serum antibody titers were monitored postvaccination. All cows in both groups were challenged with S. uberis strain UT888 by teat dip infection method for 14 consecutive days from D+35 to D+48. Clinical mastitis, bacteriological culture of mammary secretion/milk, somatic cell count, rectal body temperature and milk yield were monitored during challenge, after challenge before calving and for 30 days in milk postcalving. . The SCSP vaccine significantly reduced the incidence of clinical mastitis at the cow level (19.2%) in vaccinates compared to the control group (48%). Subclinical mastitis was also lower in vaccinates (30.8%) compared to the control group (48%), even though not statistically significant. Quarter-level clinical and subclinical mastitis were lower in vaccinates compared to the control group. Similarly, the somatic cell count was consistently lower in the vaccinates compared to the control group, although the difference was not statistically significant. The vaccine also decreased the S.uberis shedding duration from 6 to 2 days in vaccinates.

No severe adverse reactions were observed after vaccine injection, except for transient increases in rectal body temperature and injection site reactions following vaccination.Serum and milk anti-SCSP IgG titers were significantly higher in vaccinates, particularly at 30 days in milk post-calving. These results prove that the SCSP vaccine confers significant protection against S. uberis mastitis, reducing both clinical and subclinical mastitis and supporting its potential as a sustainable alternative to antibiotics for the control of S. uberis mastitis in dairy cows.