Mastitis is one of the costliest diseases in the US dairy industry, with an estimated annual loss ranging from $326 to $444 per cow. The concept of dry cow therapy started in the late 1960’s with the objective of reducing the risks for intramammary infections during the dry period and in the early stages of the subsequent lactation. Dry cow therapy (DCT) is still a common practice in the US, as shown by the 2014 USDA National Animal Health Monitoring System report, which indicated that over 90% of all cows in the US were treated with intramammary antimicrobial infusions at dry-off.
Unnecessary use of antibiotics in food producing animals for disease treatment and control can potentially lead to the emergence and spread of antimicrobial resistance, which is of great concern for both animal and human health. European countries, such as the Netherlands, have prohibited the use of blanket dry cow therapy (BDCT) since 2012. In California, similar concerns led to the approval of Senate Bill No. 27, which requires a licensed veterinarian to prescribe antimicrobial drugs (of importance to human health) to treat, control and prevent disease.
Selective dry cow therapy (SDCT) has been proposed as an alternative to the use of BDCT. When antibiotics are not used at dry off, or used only in selected cows, there are potential savings from the costs of antibiotics and labor. Despite opportunities for reduced costs, one concern includes risk of increased cases of clinical mastitis in the next lactation. Presented below is a simulated research study conducted in Europe, demonstrating the economic feasibility of selective dry cow therapy. It is important to note that the European system of dairying is different than that of California, and these results are presented for informational purposes. Future research should simulate the economics of SDCT using California data.
A group of researchers simulated 3 example herds (using European herd data; 75 cows/herd), at three different bulk tank somatic cell count (BTSCC) levels: low BTSCC (<150,000 cells/mL), average BTSCC (≥150,000 cells/mL and <250,000 cells/mL), and high BTSCC (≥250,000 cells/mL but <400,000 cells/mL). The objective of the study was to find what would be the lowest cost of mastitis associated with the dry period, while restricting the percentage of cows treated with antibiotics at dry-off. The cost of mastitis in the herd with low BTSCC was $51.30/cow/year, and this cost would be the same if 30% of the cows were not treated at dryoff. For high BTSCC herds, the cost of mastitis was $58.96/cow/year and did not change when 15% of the cows were not treated at dry-off. Although these estimates were based on simulated small European herds, the results demonstrate that there are opportunities for maintaining the costs of preventing mastitis in the dairy industry, while reducing the use of antibiotics at dry-off, even in herds with high BTSCC, or high incidence of clinical mastitis.
Do these results apply to California? Maybe. We believe that there is potential to reduce the use of antibiotics at dry-off here, too. University of California researchers, led by Dr. Sharif Aly, are exploring the best approach to choosing cows that should be treated, or not, at dry off, considering the California dairy system. Low risk cows, for instance those with low last test-day somatic cell count, and first lactation heifers or cows with no more than one case of mastitis during the previous lactation, may not need treatment at dry off. We expect to have the results of this study soon, and will be able to better understand the economic impacts of this practice for the California dairy industry. Selective dry cow therapy is a potential strategy to reduce the use of antibiotics in the dairy industry. Be on the lookout for more information regarding the research and data coming out of California.