Growth of Corynebacterium bovis in Mammary Secretions During Physiological Transitions of the Bovine Mammary Gland S. P. OLIVER1 and V. K. JUNEJA Institute of Agriculture Department of Animal Science University of Tennessee Knoxville 37901-1071 ABSTRACT
An in vitro microassay was used to evaluate growth of five strains of Corynebacteriwn bovis in mammary secretions collected from quarters of five Holstein cows at 0, 14, and 28 d of involution, at parturition, and 14 d after parturition. Variation in growth among different strains of Corynebacterium bovis was observed. Corynebacteriwn bovis grew well in mammary secretions obtained at the last milking of lactation, at parturition, and 14 d after parturition. However, growth of four strains of Corynebacteriwn bovis in mammary secretions obtained at 14 and 28 d of involution was reduced significantly. In contrast, a streptomycin-resistant strain of Corynebacterium bovis grew well in mammary secretions obtained during involution. These data suggest that mammary secretions support growth of Corynebacteriwn bovis during lactation but inhibit growth during the nonlactating period. Inhibition of growth in secretions collected during the nonlactating period may be associated with the high rate of spontaneous elimination of Corynebacterium bovis intramammary infection from cessation of milking to parturition. Conversely, enhanced growth in milk may be related to persistent Corynebacteriwn bovis intramammary infections during lactation. (Key words: Corynebacteriwn bovis. mammary secretions, dry period)
Corynebacterium bovis is isolated frequently from bovine milk during lactation (1, 3, 4, 13, IS). Little is known about C. bovis despite the observation that this organism may constitute the greatest proportion of infected quarters in many dairy herds (4, 9, 13). Infection of the bovine mammary gland by C. bovis does not appear to affect mammary secreLOry cell function, milk yield, or composition (4. 5, 19, 20). However, the number of somatic cells in milk from C. bovis-colonized quarters was increased slightly when compared with milk from uninfeeted mammary glands (1, 2, 4, 5). The increase in SCC was considered slight, since the geometric mean SCC was .5 cfu (loglO)/mI.
At the last milking of lactation, 4 quarters were infected by coagulase-negative staphylococci and 11 quarters were infected by C. bovis. Coagulase-negative staphylococci were isolated from 1 mammary quarter only at 14 and 28 d of involution, and all remaining quarters were bacteriologically negative. At parturition, coagulase-negative staphylococci were isolated from three quarters, and 17 quarters were negative. During early lactation, coagulase-negative staphylococci and C. bovis were isolated from 6 and 2 quarters, respectively. No new major pathogen IMI occurred in experimental cows throughout the study. Growth of C. bovis in mammary secretions of four cows was similar (Table 1). However, growth of C. bovis in mammary secretions from one cow was lower (P