title: The incidence and aetiology of clinical bovine mastitis on 14 farms in Northland, New Zealand.
abstract: OBJECTIVE
  To estimate the incidence of clinical mastitis and the frequency of isolation of mastitis-causing organisms from clinical cases in one lactation season (July 2005 to May 2006) on 14 dairy farms from the Northland region of New Zealand.
  
  
  METHODS
  Cases of clinical mastitis were determined by trained farm personnel who recorded the identity of affected cows. Pooled milk samples from affected quarter(s) were aseptically collected by the farm personnel, for microbiology. Mean numbers of affected cows and quarters were compared at the population and farm level per 305 cow-days-at-risk (DAR).
  
  
  RESULTS
  One or more cases of clinical mastitis occurred in 559/3,765 (14.8%) lactating cows. The average incidence of clinical mastitis was 0.19 cases per 305 DAR. The incidence in rear quarters (56.2%) was 1.3 times (p=0.027) that of front quarters (43.8%). The incidence of clinical mastitis and numbers of affected quarters were significantly influenced by the stage of lactation (higher in early lactation), age (higher in older cows) and farm. At the cow level, the most common isolates were Staphylococcus aureus (23.7%) and Streptococcus uberis (23.3%). No causative organisms were identified in 19.9% of the samples. Each cow had an average of 1.8 quarters affected during a case of clinical mastitis.
  
  
  CONCLUSIONS
  This study demonstrated a higher incidence of staphylococcal clinical mastitis on dairy farms from Northland than has been reported in other regions of New Zealand.
authors.affiliation: Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North 4442, New Zealand. k.r.petrovski@massey.ac.nz
authors.forename: K R
authors.initials: KR
authors.lastname: Petrovski
authors.forename: C
authors.initials: C
authors.lastname: Heuer
authors.forename: T J
authors.initials: TJ
authors.lastname: Parkinson
authors.forename: N B
authors.initials: NB
authors.lastname: Williamson
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D002417:Cattle; D005260:Female; D006094:Gram-Positive Bacteria / Q000302:isolation & purification; D015994:Incidence; D007774:Lactation; D008137:Longitudinal Studies; D008414:Mastitis, Bovine / Q000453:epidemiology* / Q000209:etiology* / Q000382:microbiology; D008892:Milk / Q000382:microbiology; D009520:New Zealand / Q000453:epidemiology; D012307:Risk Factors; D013211:Staphylococcus aureus / Q000302:isolation & purification; D013291:Streptococcus / Q000302:isolation & purification; D013997:Time Factors