Dry cow therapy is the use of intramammary antibiotic therapy immediately after the last milking of lactation. Using Food and Drug Administration (FDA)-approved infusion products at drying off can decrease the number of existing infections and prevent new infections during the early weeks of the dry period. Most herds benefit by treating every quarter of every cow at drying off. This approach will reach all infected quarters, is more effective than selective treatment in preventing new infections early in the dry period, and does not require laboratory screening procedures. Selective dry cow treatment has been considered by some dairy producers. However, selective treatment may fail to reach 20 to 40 percent of infected quarters in a herd. Also, quarters not treated at drying off are more likely than treated quarters to become infected during the dry period. Most studies indicate that if the decision is based on economics (i.e., the cost of dry cow therapy compared to the return to the producer), treating every quarter of every cow at drying off is preferable. Source: National Mastitis Council www.nmconline.org
Treated cows should be tested with an antibiotic screening test at the end of the withholding period and before milk is added to the tank, especially if dry periods were less than 56 to 60 days. Cows with 30- to 35-day dry periods should probably be treated at drying off with a lactating product rather than a dry treatment.
Dry cow therapy is indeed difficult to impossible to use selectively. Many producers and herd managers use a combination of recent recollection of clinical signs (many herds still do not adequately record clinical mastitis episodes, including those using computerized records) or the most recent somatic cell count if that is even tested on a regular basis. Therefore, many infected quarters are not selected for dry treatment unless every functioning quarter of every cow is treated at dryoff. Because there is some prevention of new infections, it is logical to treat even quarters not infected at dryoff. Dry treatment of all quarters is one of the most cost-effective mastitis control practices.
Dave Wilson, Utah State University Dairy Extension Veterinarian
