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National Animal Health Monitoring System Report on Mycoplasma Mastitis

Posted: June 5, 2005

They indicate that mycoplasma mastitis can be economically devastating to dairies because of its contagious nature and its resistance to treatment.

The National Animal Health Monitoring System (NAHMS) Dairy 2002 study, conducted by the Animal and Plant Health Inspection Service of the USDA, reported on Mycoplasma in Bulk Tank Milk on U.S. Dairies. They indicate that mycoplasma mastitis can be economically devastating to dairies because of its contagious nature and its resistance to treatment. Moreover, Mycoplasma sp. are fastidious organisms that grow very slowly, requiring complex media and special growth conditions. This makes it difficult to detect these agents. Many mastitis diagnostic laboratories do not routinely culture milk for mycoplasma. Perhaps because of the special needs and associated costs of culture for Mycoplasma sp., mycoplasma mastitis is most routinely monitored via bulk tank cultures at more specialized laboratories. The NAHMS study assessed the prevalence of dairy bulk tank milk in four regions of the U.S.: West (CA, CO, ID, NM, TX, and WA); Midwest (IL, IN, IA, MN, MI, MO, OH, and WI); Northeast (NY, PA, and VT); and Southeast (FL, KY, TN, and VA). Overall, 7.9% of the dairies tested had at least one bulk tank milk sample that was positive for Mycoplasma sp. The West had the greatest number of bulk tank positive mycoplasma cultures (9.4%), followed by the Southeast (6.6%), Northeast (2.8%), and Midwest (2.2%). Eighty-six percent of the samples had M. bovis, and the remaining 14% were comprised of M. californicum, M. alkalescens, M. canadense, and M. bovigenitalium. Larger herds (>500 cows) were more likely to have a positive bulk tank culture (21.7%), followed by medium herds (100-499 cows, 3.9%) and smaller herds (2.1%). Thus perhaps mycoplasma mastitis is not as much a regionally associated problem as it is a herd size problem or an expanding herd problem. Dairies in the West (23.2%), are more likely to have 500 cows, followed by 4.9% for the Southeast, 1.9% for the Northeast, and 1.2% for the Midwest (USDA National Agricultural Statistics Service). The correlation between mycoplasma positive bulk tanks and regional percentage of dairy herds greater than 500 cows, is approximately 0.82, where 1.0 would be a perfect correlation. Other studies have confirmed that larger herds tend to have a greater prevalence with mycoplasma mastitis. It is assumed that the introduction of new cattle into a herd is associated with mycoplasma mastitis problems, and it is assumed that larger herds are more likely to bring cattle into a herd through expansion or maintenance of herd size. Thus the authors of the NAHMS study conclude that purchased cattle should be screened for mycoplasma mastitis. Additionally they urge the strict use of milking time hygiene techniques, always a good idea for the control and prevention of the spread of contagious mastitis.

Larry Fox, Field Disease Investigative Unit, Washington State University