[Attempts at preventing experimental Staphylococcus aureus mastitis by immunization and intramammary insertion of a...

The susceptibility of lactating cows to experimental challenge with two strains of Staphylococcus aureus was investigated 30 days after calving. These cows were previously immunized during the dry-period and udder quarters were fitted at drying-off with a polyethylene intramammary device (IMD). Incidence of infection recorded in device-fitted quarters and control quarters was not significantly different. There was no difference between IMD-fitted and control quarters in milk yield, contents in butterfat and protein. Lactose mean concentration was significantly decreased in milk collected from quarters fitted with polyethylene loop (P less than 0.05). The somatic cell counts in milk from quarters depended on: a) fraction collected, b) time of sampling, c) presence of intramammary loop, d) result of experimental challenge. Milk somatic-cell counts determined at mid-lactation for fractions collected before udder stimulation and total milk in IMD fitted quarters were greater than for control quarters (P less than 0.05). In general, these differences were greater in quarters which were experimentally infected than uninfected quarters. The count in total milk collected at mid-lactation for uninfected device-fitted quarters averaged 720 000 cells/ml.