Controlling Contagious Mastitis
Robert J. Harmon
University of Kentucky
Staphylococcus aureus and Strep. agalactiae are the common contagious mastitis pathogens (3, 28). The major reservoir for these pathogens is the infected udder, and infections are spread among cows or between quarters during the milking process by contaminated milking equipment, milker's hands, or cloths or sponges used to wash or dry more than one cow. Infections tend to be chronic (i.e., long duration) and subclinical with periodic clinical episodes. Thus contagious mastitis results in decreases in milk production and increases in bulk tank SCC, but there may be few visible symptoms, i.e. this tends to be a hidden form of mastitis. Herds with high bulk tank SCC tend to have high levels of infections by contagious pathogens.
Streptococcus dysgalactiae is generally characterized as an environmental pathogen, but also may have characteristics of a contagious organism and appears to spread from cow to cow (28). This pathogen is generally responsive to teat dipping and dry cow therapy, but new infections can occur in a herd when no other udder infections by this organism are present. Corynebacterium bovis is considered a minor pathogen (9). The main reservoir appears to be infected udders or teat ducts, and this organism is spread rapidly from cow to cow in the absence of adequate teat dipping. Infections by C. bovis cause only moderate inflammation with SCC exceeding those of uninfected glands by only two- to threefold. Infections are infrequently the major cause of elevated bulk tank SCC, clinical mastitis, marked compositional changes, or dramatic decreases in milk production.
Mycoplasma species are contagious pathogens that are rare in some areas but not uncommon in others (5). Mycoplasma bovis is the most common species and probably causes the most severe problems. Some characteristics of mycoplasma mastitis include sudden onset, rapid spread in the herd, marked reduction in milk production, and resistance to treatment. Veterinary assistance is recommended for the diagnosis and control of mycoplasma mastitis, because special bacteriological culture procedures are necessary for diagnosis.