Locus of Mammary Gland Infections of Corynebacterium bovis

Corynebacterium bovis was shed in 33.5 and 38% of aseptically drawn milk samples from two university dairy herds. Individual quarters were examined to determine locus of infection. C. bovis was cultured from only 5 of 20 samples drawn by syringe from the teat cistern but was in each of the 20 samples drawn through the streak canal. Counts of C. bovis averaged 23,000 from cross sections of streak canal of about 1mm thickness. Numbers of C. bovis were fewer in Furstenberg's rosette and none was recovered from sections of the teat cistern. C. bovis was microscopically visible in ultra-thin sections of streak canal and appeared closely associated with keratinaceous tissues. Numbers were greater than those enumerated by the broth method. There was no microscopic evidence of damage to streak canal tissue from C. bovis in infected and noninfected tissues after staining with hematoxylin and eosin. Results suggest that C. bovis is not established past Furstenberg's rosette.