Infectious bovine mastitis caused by environmental organisms.

The purpose of this study was to determine the prevalence of environmental mastitis in dairy herds and identify the main environmental pathogens, and to evaluate the influence of season, housing and management. A total of 20,310 quarters of 5216 animals from 52 dairy herds in 32 counties was examined. Milk samples were aseptically collected for laboratory examination from mammary glands testing positive to any of the field tests. From these, 736 environmental infections were identified. The most frequently isolated environmental pathogens were algae of the genus Prototheca sp. (41.2%), Streptococcus uberis (21.1%), fungi (19.5%), enterobacteriacea (8.3%) and Nocardia sp. (6.6%). The occurrence of mastitis was not influenced by the herd size, use of dry cow therapy, or post milking teat dipping. A tendency for increased occurrence of environmental mastitis during the months of September to February (hot and wet weather) was observed, suggesting a seasonal influence.