Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Animal Science

Major Professor

S.P. Oliver


Objectives of this study were to determine whether Corynebacterium bovis colonization protected lactating bovine mammary glands from experimentally induced Streptococcus uberis infection and to determine whether dose responses or strain differences existed with respect to induction of experimental Strep. uberis infection. Further objectives were to induce experimental C. bovis colonization in lactating bovine mammary glands by inoculating organisms directly into the streak canal and to determine effects of C. bovis colonization on milk composition and number of somatic cells.

Twenty-two quarters colonized with C. bovis, one quarter infected with Staphylococcus aureus, and four uninfected quarters were inoculated four to five mm into the streak canal with 3 x 104 Colony-Forming Units (CFU) of a strain of Strep. uberis isolated from a case of clinical mastitis. Streptococcus uberis was isolated from all quarters by 48 hr postinoculation. All quarters had clinical mastitis, number of somatic cells increased, and daily milk production decreased during the experimental period. Most cows had elevated body temperatures by 24-72 hr postinoculation. Subsequent elevated temperature and reisolation of Strep. uberis occurred in many instances following both intramammary and systemic antibiotic treatment.

A reduced concentration (110 CFU) of the same strain of Strep. uberis caused equally severe mastitis when inoculated four to five mm into the streak canal of three quarters colonized with C. bovis and one uninfected quarter in two animals. Streptococcus uberis was isolated from all inoculated quarters and all quarters had clinical mastitis by 48 hr postinoculation. One cow had an elevated body temperature by 96 hr postinoculation. Milk production decreased markedly by 84 hr and returned to near preinoculation levels in both cows within 12 days postinoculation. Number of somatic cells were greatly elevated in inoculated quarters. Corynebacterium bovis did not protect lactating mammary quarters from experimental Strep. uberis (isolate 850366-1) infection, nor did it reduce severity of induced infection.

In two separate trials, two quarters infected with Staphylococcus aureus, three quarters colonized with C. bovis, and three pathogen-free quarters were inoculated with 25-240 CFU Strep. uberis (ATCC 27958). Streptococcus uberis was not isolated from quarters following inoculation. No changes in milk yield or appearance were observed.

Colonization of lactating bovine mammary glands with a streptomycin resistant strain of Corynebacterium bovis (isolate 82-872a) was established in eight of 38 (21.1%) quarters following intramammary inoculation of 790 CFU four to five mm into the streak canal. Number of somatic cells remained significantly higher than preinoculation levels 23 days following inoculation. Eleven quarters of eight cows not colon ized following inoculation of 790 CFU C. bovis were reinoculated with successively higher concentrations until all quarters became colonized. Susceptibility to C. bovis colonization was related to concentration of organisms inoculated. All quarters were colonized by the time the inoculum contained 8.0 x104 CFU C. bovis. In the majority of cases, C. bovis colonization persisted throughout the experimental period. No changes in percent lactose, protein, fat, or solids-not-fat were detected in quarter foremilk samples following C. bovis colonization. Milk was normal in appearance and body temperature was not affected following C. bovis colonization.

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