Observed reduction in recovery of Corynebacterium spp. from bovine milk samples by use of a teat cannula

Although Corynebacterium bovis and coagulase-negative staphylococci are frequently the most commonly isolated bacteria from milk samples submitted for identification of pathogens causing intramammary infection, the individual quarter somatic cell count (SCC) from those samples is most often low. The present study aimed at evaluating the difference in bacteriology results from milk sampled by the standard technique (as recommended by the National Mastitis Council) and by the use of a teat cannula surpassing the teat canal, since C. bovis is often only found in the teat canal. Single quarter milk samples were collected in duplicate from 132 dairy cows on a commercial dairy farm using the standard milk sampling technique and also using a cannula introduced into the teat. Two groups of quarters were sampled: a group that was selected randomly at cow and quarter level and a group that was selected based on having SCC >200 000 cells/ml at the previous milk recording at cow level and on California mastitis test result at quarter level. Bacteriological culture performed on the samples yielded 29 Corynebacterium spp. isolates from the samples collected with the standard technique and 6 isolates from the samples collected with a cannula. Bacteriological culture yielded 73 and 100 culture negative samples respectively with the standard and the alternative sampling technique. A significant difference between the two sampling techniques was observed for recovery of Corynebacterium spp. and for no-growth samples. There was no significant difference in the isolation of Corynebacterium spp. or other bacterial species when using the standard technique before or after sampling with the cannula; thus the observed difference in bacteriology results could not be attributed to a particular sampling order. No significant change was observed overall in individual quarter SCC measured on the sampling day and 7 d later. Our results agree with several studies showing that Corynebacterium bovis often colonizes the teat canal, without causing true intramammary infection.