Efficacy of different Lysigin formulations in the prevention of Staphylococcus aureus intramammary infection in dairy heifers.

The objective was to compare the efficacy of two experimental Staphylococcus aureus mastitis bacterins and a currently marketed five-isolate-based Staph. aureus bacterin (Lysigin, Boehringer Ingelheim Vetmedica, Inc.) with unvaccinated controls. Forty-seven Holstein-Friesian heifers were randomly assigned to one of four groups such that Group 1 (n=11) received a three-isolate experimental bacterin, Group 2 (n=11) received a five-isolate experimental bacterin, Group 3 (n=14) received Lysigin, and Group 4 (n=11) served as unvaccinated controls. Vaccinations were administered twice 28 d apart in late gestation. All groups were challenged with a heterologous strain of Staph. aureus (ATCC 29740) on days 6, 7, and 8 of lactation. Mastitis score, somatic cell count (SCC), milk culture yield, and total daily milk yield data were collected before and after challenge. All 47 cattle developed a Staph. aureus IMI post-challenge with three animals in Group 1 and one animal in Group 3 clearing their Staph. aureus IMI by the end of the study. However, there was no evidence of a difference between vaccinates and control with regard to Staph. aureus clearance rates post-challenge (P> or =0.214). Cattle vaccinated with Lysigin had a lower mean duration of clinical mastitis and lower total mastitis score post-challenge than controls (P=0.045 and P=0.046, respectively). Overall, there was no evidence that any of the vaccinated groups had a lower mean SCC than control (P> or =0.148) for the tested study days. Likewise there was no evidence that vaccinates had greater milk yield than controls post-challenge (P=0.617). Hence, there was no evidence that the vaccines reliably prevented Staph. aureus IMI, but Lysigin showed benefit in reducing the clinical severity and duration of clinical disease post-challenge. Neither of the experimental bacterins appeared to perform better than Lysigin.