Una creciente preocupación pública por la seguridad alimentaria y la resistencia a los antimicrobianos, reflexionar sobre el dogma de la calidad de la leche no es una mala idea. A pesar del éxito de la terapia con vacas secas para prevenir y curar infecciones intramamarias durante el período seco, el panorama de la mastitis ha cambiado en los 50 años desde que esta herramienta de manejo se aplicó por primera vez.
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El tratamiento de todas las vacas en la desecación con infusiones antimicrobianas en cada trimestre ha sido una pieza clave del control de la mastitis. Una encuesta de 2013 de más de 600 rebaños descubrió que el 85% de los rebaños usan terapia de vaca seca en manta, y los recuentos de células somáticas en tanques a granel tienden a ser más bajos en rebaños que usan esa práctica. 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. DIFFERENT BACTERIA The predominant mastitis-causing bacteria in many herds have shifted from contagious to environmentalreservoirs, 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