title: Culture results from milk samples submitted to veterinary diagnostic laboratories from August 2003 to December 2006 in New Zealand.
abstract: OBJECTIVE
  To determine the pattern of isolation of major mastitis-causing organisms isolated from milk samples submitted to five veterinary diagnostic laboratories in New Zealand.
  
  
  METHODS
  The culture results of 25,288 milk samples that were collected from dairy cows throughout New Zealand from August 2003 to December 2006 and submitted to a group of veterinary diagnostic laboratories were assembled, reviewed and summarised. Logistic regression was used to analyse the effect of year, region (i.e. North vs South Island), and season on the probability of isolating the two most common organisms.
  
  
  RESULTS
  The most commonly isolated mastitis causing organisms from all samples were: Streptococcus uberis (23.6%), Staphylococcus aureus (23.5%), coagulase-negative staphylococci (CNS; 7.2%), Strep. dysgalactiae (6.2%), Bacillus spp. (4.0%), and coliforms (3.7%). The percentage of samples with isolates of Strep. uberis or Staph. aureus was affected by island, year and season (p<0.001). For most of the year, except in late winter and early spring when Strep. uberis was much more common, the percentage of isolates of Strep. uberis and Staph. aureus were not apparently different despite the former being an environmental pathogen and the other a contagious one.
  
  
  CONCLUSIONS
  The pattern of isolation of major mastitis-causing organisms, as determined from culture of milk samples submitted to diagnostic laboratories in New Zealand, has changed significantly over the last 40 years, with a substantial increase in the percentage of isolates that are Strep. uberis and a decrease in isolates of Strep. agalactiae. There is a clear seasonal pattern to the isolation of both Strep. uberis and Staph. aureus, particularly the former.
  
  
  CONCLUSIONS
  Knowledge of the aetiological agents causing bovine mastitis on a farm is of value in determining the choice of treatment. This dataset shows that, although there is seasonal pattern to the isolation of mastitis-causing organisms in New Zealand, both Strep. uberis and Staph. aureus are isolated throughout the year, so bacteriology is of value in determining aetiology even in late winter/early spring.
authors: Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand. k.r.petrovski@massey.ac.nz
authors: K R
authors: KR
authors: Petrovski
authors: N B
authors: NB
authors: Williamson
authors: N
authors: N
authors: Lopez-Villalobos
authors: T J
authors: TJ
authors: Parkinson
authors: I G
authors: IG
authors: Tucker
mesh_terms: D000818:Animals; D001424:Bacterial Infections / Q000175:diagnosis / Q000453:epidemiology / Q000662:veterinary*; D001431:Bacteriological Techniques; D002417:Cattle; D005260:Female; D008414:Mastitis, Bovine / Q000453:epidemiology / Q000382:microbiology*; D009520:New Zealand / Q000453:epidemiology; D012189:Retrospective Studies; D013997:Time Factors