Name the reservoir first

Contagious pattern: Staphylococcus aureus and Streptococcus agalactiae are primarily maintained in infected udders, teat lesions, and infected cows. Spread commonly occurs during milking through liners, hands, towels, and other contaminated equipment. Look for cow-to-cow clustering, repeat infections, rising somatic cell counts, or cases concentrated in the parlor.

Environmental pattern: Coliforms such as E. coli and Klebsiella, plus environmental streptococci including Strep. uberis and Strep. dysgalactiae, are associated with feces, manure, soil, water, and bedding. Risk rises when bedding is wet or heavily soiled and during the post-milking period, when the teat canal is more exposed. Fresh-cow and housing-group clusters should shift attention toward stalls, packs, cleanliness, and the hours after milking.

The split is useful epidemiology—not a moral label. S. uberis and some coliform strains can show mixed or strain-specific behavior, so do not infer the reservoir from the organism's name alone.

Map cases by cow, quarter, time in lactation, milking group, housing, bedding condition, and culture result. Pair clean sampling with routine culture or an evaluated on-farm culture program, and review results with the herd veterinarian. Culture-negative and many Gram-negative cases may be self-limiting, but severe disease still needs prompt veterinary assessment. Use the evidence to target hygiene, equipment, segregation, bedding, and treatment decisions—without guessing at drug doses.