SYMPOSIUM: ENVIRONMENTAL EFFECTS ON COW HEALTH AND PERFORMANCE Environmental Mastitis: Cause, Prevalence, Prevention 1,2

Rate of intramammary infection by coliform bacteria and species of streptococci other than Streptococcus agalactiae (environmental pathogens) was studied in a dairy herd in total confinement. Rate was higher during the dry period than during lactation and increased progressively as parity increased. Rate was maximal during summer and coincided with maximum exposure to coliforms in bedding. Streptococcal infections were longer than coliform. Approximately 59% of streptococcal infections and 69% of coliform infections were present for 30 lactation days or less. Percent quarters infected by day of year varied between .7 and 3.0% for coliform bacteria and between 1.6 and 4.7% for streptococci. Approximately 81% of coliform infections and 53% of streptococcal infections during lactation were clinical. Clinical cases were highest during the first 76 days of lactation and during summer. Only 6.7% of coliform infections resulted in acute coliform mastitis, and all acute cases were during summer or early lactation. Dry cow therapy reduced rate of streptococcal infection during the early dry period but was without effect during the prepartum period. There was no effect of dry cow therapy on coliform infection rate during the dry period.