The incidence and aetiology of clinical bovine mastitis on 14 farms in Northland, New Zealand

Abstract

AIM: 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 signifi cantly infl uenced 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 identifi ed 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.

KEY WORDS:

• Mastitis
• dairy cows
• Staphylococcus aureus
• Streptococcus uberis
• Northland

Acknowledgement

Financial support provided by the Northland Community Foundation, in cooperation with the Northern Wairoa Veterinary Club, Dargaville Field Days, and Maungatapere Veterinary Clubs Charitable Trust, is gratefully acknowledged. The authors are indebted to all farm owners and farm personnel of collaborating dairy farms for their friendship, cooperation and interest in the research. Thanks also to the staff of the Dargaville Veterinary Centre for their assistance and encouragement during field work. Thanks also to Kevin Lawrence and Richard Laven for assistance with the statistical analysis of the data, and Michelle McKeany and Rae Pearson at the New Zealand Veterinary Pathology Laboratory in Palmerston North for their help in culturing milk samples.