Treatment of all cows at dryoff with antimicro-bial infusions in each quarter has been a linchpin of mastitis control. A 2013 survey of over 600 herds found that 85% of herds use blanket dry-cow therapy, and bulk tank somatic cell counts tend to be lower in herds that use that practice.
However, with increased public concern over food safety and antimicrobial resistance, reflection on milk quality dogma is not a bad idea. Despite the success of dry-cow therapy to prevent and cure intramammary infections over the dry period, the landscape of mastitis has changed in the 50 years since this management tool was first applied.
The predominant mastitis-causing bacteria in many herds have shifted from contagious to environmental-reservoirs, such as coliforms. Improved housing, bedding, feeding and the use of internal teat sealants have all helped reduce the rate of intramammary infections during the dry period.
Selective dry-cow therapy, or treatment at dryoff of only infected cows, might be an option. Before you consider selective dry-cow therapy, you must have all other parts of your milk quality program in place and protocols consistently followed. Herds with bulk tank somatic cell count (SCC) over 200,000 cells/mL are not the best candidates. Milk quality metrics need to be tracked regularly. Also, the decision to treat or not treat cows has to be based on sound information regarding infection status of each cow.
Herd-specific plans, at the very least, must include clinical mastitis history and individual cow SCC before dryoff. Also, most studies suggest a second tier of selection, bacterial culture of low-SCC cows, should be added before giving the “green light” not to treat a cow at dryoff.
AVOID SPEED BUMPS
There are a few speed bumps for selective dry-cow therapy beyond constructing an evidenced-based treatment selection protocol.
In the U.S., fewer herds are tracking subclinical mastitis. Without this information, it is nearly impossible to track the impact of changes in dry-cow treatment programs — bulk tank SCC are inadequate to measure change. Because of greater emphasis on parlor efficiency, increased rate of cow throughput in many larger dairies pressures milking operators to not spend time stripping milk from teats, let alone identify clinical mastitis. Thus, critical outcomes to assess the efficacy of change in a dry-cow therapy program, such as new and cured infections over the dry-cow period, and clinical mastitis in the first 30 to 60 days in milk, will be unavailable in these herds. Also, less than 15% of herds incorporate milk culture, stating labor is an issue.
Blanket dry-cow therapy also has risks, such as employees who are poorly trained in infusion techniques. But increased mastitis in early lactation, as a result of a poorly designed or executed select dry-cow therapy protocol, can be costly. Cows with a first test date SCC ≥ 200,000 cells/mL produce about 1,600 lb. less milk than cows with first test date SCC
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