Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School



Mastitis remains the most costly disease of dairy cattle. The annual loss to the dairy industry in the United States from this disease has been estimated between $225 and $500 million per year. Ninety to 95% of infectious mastitis is reported to be associated with Streptococcus agalactiae or Staphylococcus spp. Staphylococcus aureus and others of the family Micrococcaceae are reported to be the second most commonly found udder pathogens. The pathogenesis of staphylococcic mastitis remains poorly understood. Some research data have indicated that the disease is essentially contagious, and that the source of the organism is an infected udder, and transmission is accomplished through milker's hands and through milking equipment. Other data have indicated that the organisms involved are more or less ubiquitous on the body of the dairy cow and in her environment, and that these organisms act as opportunists whose virulence is increased by certain predisposing factors. In this study gram positive, spherical organisms which occurred in clusters and produced catalase are referred to as micrococci. The vernacular name, micrococci, as used in Bergey's Manual of Determinative Bacteriology, 7th edition, pp. 454-455, generally includes all the organisms of the family Micrococcaceae. Because of the methods used for isolating organisms in this investigation, only the organisms capable of aerobic growth are included. This encompasses mainly organisms of the genera Staphylococcus and Micrococcus but since no attempt was made to distinguish them, organisms of the genera Gaffkya and Sarcina are included. Organisms of the latter 2 genera were classified as Staphylococcus sp. or Micrococcus sp. according to their ability to form acid from glucose under anaerobic conditions.

Library of Congress Subject Headings

Udder -- Diseases


Dairy cattle -- Diseases

South Dakota State University Theses



Number of Pages



South Dakota State University