District-wide herd sanitation and eradication of intramammary Staphylococcus aureus genotype B infection in dairy herds in Ticino, Switzerland.

The present study demonstrates successful herd sanitation and eradication of contagious mastitis caused by Staphylococcus aureus genotype B (GTB) in an entire Swiss district (Ticino) including 3,364 dairy cows from 168 farms. Herd sanitation included testing of all cows using a highly GTB-specific and sensitive real-time quantitative PCR (qPCR) assay, implementation of related on-farm measures, appropriate antibiotic therapy of GTB-positive cows, and culling of therapy-resistant animals, respectively. A treatment index was used as an objective criterion to select GTB-positive cows eligible for culling and replacement payment. Sixty-two herds (37%) were initially GTB-positive with a cow prevalence between 10% and 100% and were submitted to sanitation. Twenty months after the start of the campaign, all of these herds were free from S. aureus GTB, whereby 73% of them were sanitized during the first 7 mo. At the cow level, a total of 343 animals were infected. Fifty of them were immediately culled and farmers were financially compensated based on their treatment index value _. The remaining 293 cows were intramammarily treated with antibiotics either during lactation using the combination of cephalexin-kanamycin or penicillin-gentamicin or at dry-off using cloxacillin. Out of these cows, 275 (93.9%) were treated successfully, meaning that their milk was twice GTB-negative by qPCR after therapy. For lactational treatment, control samples were taken ≥10 and ≥20 d after treatment, for dry-off treatment ≥14 and ≥24 d after parturition. Neither lactation number nor SCC before treatment of the cow nor the type of therapy was associated with therapeutic cure. Using data of 30 GTB-positive and 71 GTB-negative herds (1,855 observations), the effect of GTB sanitation on bulk tank milk SCC (BTSCC) was evaluated by applying a linear mixed statistical model. In the year before sanitation, BTSCC was always higher in GTB-positive than in GTB-negative herds. After the start of the campaign, BTSCC declined rapidly in the herds under GTB sanitation and achieved values that no longer differed statistically from those of GTB-free herds after only 2 mo, remaining very similar for the rest of the campaign. The farmers were very satisfied with the outcome of the campaign because all GTB-positive herds could be sanitized rapidly, sanitation was sustainable, and milk quality increased.
(The Authors. Published by Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)