Reduction of Antibiotics at the Dry Period

Project entitled:

Selective Treatment during the Dry Period

Jean-Philippe Roy, Marguerite Cameron, Greg Keefe


Most antibiotics used on dairy herds are for treating and preventing bovine mastitis. In North America, antibiotic treatment at drying-off is universally recommended for all of a herd’s cows after the last milking. New non-antibiotic products are now available to combat mastitis, including internal sealant or selective bacterial culture media usable on a farm (Petrifilm®). Some dairy herds are able to maintain a somatic cell count under 250,000 cells/ml. These properly controlled herds could receive selective intramammary treatment during the dry period without a negative impact on their overall health or milk production. The benefits of selective treatment during the dry period include reduced costs, a lower amount of antibiotic used and, consequently, a lower risk that there will be a presence of antibiotic residues and that bacterial resistance will develop. A total of 720 cows from 16 herds met our inclusion criteria—358 in the culture group, and 362 in the control group. A total of 47% of culture group cows did not receive antibiotics during the dry period. The proportion of infected cows at calving, the incidence of clinical mastitis during early lactation and milk production were not significantly different between groups. A comparison of economic margins between the control group and the culture group concluded that the savings associated with the use of selective antibiotic treatment during the dry period was $8.70 per cow. The Petrifilm tests were adequately reliable. A questionnaire administered to participating dairy farmers showed that all farmers found interpreting the Petrifilm plates to be easy or very easy.