Mastitis pathogens present in bulk tank milk from seven dairy herds in the Waikato region, New Zealand.
OBJECTIVE
To identify and enumerate colony forming units (cfu) of mastitis pathogens in bulk tank milk (BTM) from pasture-fed New Zealand dairy cows in the Waikato region.


METHODS
BTM samples from seven seasonal-calving dairy herds in the Waikato region were collected monthly from August to December 2004 (cows calved during July-September). Milk samples were cultured on blood aesculin and MacConkey agar plates for 24 h, and the number of mastitis pathogens identified and counted.


RESULTS
Colonies identified in BTM included aesculin-positive streptococci, Staphylococcus aureus, coagulase-negative staphylococci (CNS), and coliforms; counts ranged from zero to >1,000 cfu/ml. Counts>1,000 cfu/ml for total aesculin-positive streptococci, CNS and coliforms were present in 48%, 51% and 11% of BTM samples, respectively. Counts of Staph. aureus ranged from zero to 1,000 cfu/ml, but first appeared in BTM samples only in October. Staphylococcus aureus was repeatedly isolated in BTM from 4/7 farms during the testing period.


CONCLUSIONS
Counts of mastitis pathogens in this study appeared high relative to interpretive criteria set by other workers, which may indicate a high prevalence of mastitis risk factors on these farms. Interpretation of results is difficult as aesculin-positive streptococci, CNS and coliforms can be isolated from the environment as well as from cows with clinical or subclinical mastitis. Furthermore, Staph. aureus is inconsistently excreted from infected bovine mammary glands. More extensive study of this method is required in New Zealand to attempt to further validate the interpretation of results of bacterial culture of BTM.


CONCLUSIONS
This method may be used to monitor challenge from mastitis pathogens over time as part of milk quality control programmes. The technique may be of use as a screening test to provide information to veterinarians, affording them the opportunity to have an input into mastitis control on dairy farms in New Zealand.
Howard
P
P
South and Mid Canterbury Veterinary Services Limited, King Street Temuka, New Zealand. parklands.TA@xtra.co.nz
D000818:Animals; D002417:Cattle; D015169:Colony Count, Microbial / Q000662:veterinary; D005260:Female; D008414:Mastitis, Bovine / Q000382:microbiology* / Q000517:prevention & control; D008892:Milk / Q000382:microbiology* / Q000592:standards; D009520:New Zealand; D012621:Seasons; D013203:Staphylococcal Infections / Q000382:microbiology / Q000517:prevention & control / Q000662:veterinary*; D013290:Streptococcal Infections / Q000382:microbiology / Q000517:prevention & control / Q000662:veterinary*