The objective of this study was to investigate responses to an intramammary infusion of a Streptococcus uberis strain in 264 Friesian-Jersey cows, and identify factors contributing to clinical mastitis risk in the week following infusion. Factors examined for their contribution to risk include sire, days in milk at the time of infusion, SCC on the morning of infusion, previous mastitis treatment history, and the presence of any major pathogens at the time of infusion. Prior to infusion, milk samples were collected from all glands for bacteriology assessment, and antibiotic treatments were administered to clear infections. A single gland from each cow was infused with an average 104 colony-forming units (sd=22) of Streptococcus uberis, and milk samples were collected at each milking for the subsequent 13 milkings, or until diagnosis of clinical mastitis. Logistic regression and survival analysis were used to determine risk factors. Findings showed that cows with a somatic cell count at infusion of ≥100,000 cells/ml had a lower incidence of clinical mastitis (18.3% vs. 81.5%; p<0.0001). Results also indicated that the presence of Staphylococcus aureus at infusion for cows that had no pre-infusion mastitis treatment(s) was associated with a lower incidence of clinical mastitis (29.0% vs. 82.8%; p<0.0001).

KM, Sanders, S McDougall, GE Stanley, DL Johnson, RJ Spelman, and SJ Harcourt

Proceedings of the New Zealand Society of Animal Production, Volume 66, Napier, 70-76, 2006
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