Incidence of Staphylococcus aureus in cows' milk following mucosal and parenteral administration of autogenous S. aureus vaccine during the dry period

Abstract

A prospective study was performed for a 12 month period during which a group of 90 cows from two different dairy farms were vaccinated with herd-specific autogenous Staphylococcus aureus vaccines. The IgA response as well as the incidence of S. aureus in the milk was evaluated. Each herd was clinically evaluated before vaccination and the data recorded as a base line for udder health and group diversity. Vaccination was administered on the mucosal surfaces of the vagina and teat canal as well as intra-muscularly (IM). The first vaccination was done at dry-up via the intra-teat and IM routes and the second vaccination at steam-up via the intra-vaginal and IM routes. Pre-vaccination (at dry-up), and post calving (at monthly intervals) milk samples were tested for S. aureus specific IgA with ELISA. The same milk samples were also cultured for S. aureus. The vaccinated and un-vaccinated groups were further stratified according to the presence or absence of S. aureus in milk cultured at dry-up. Data was analysed over time according to lactation stage. The fate of all cows was recorded throughout the study. The incidence of S. aureus in milk from vaccinated and un-vaccinated groups was evaluated using McNemars Test. Although the incidence of new cases were insignificant in both groups the risk for development of new cases of S. aureus was lower in the vaccinated group, 24% ,than in the un-vaccinated group,36%. Comparison of IgA titres between vaccinated and un-vaccinated groups on the respective farms was only done for cows that did not culture any S. aureus for the duration of lactation. There were no significant differences for IgA titres between the two groups except between the fourth and fifth month of farm 2 where the vaccinated group showed a higher titre. The interpretation of serum conversion was complicated by the diversity of the groups and presence of natural S. aureus infection.