Epidemiologic analysis of Mycoplasma spp isolated from bulk-tank milk samples obtained from dairy herds that were members of a milk cooperative.

OBJECTIVE: To determine the prevalence of Mycoplasma spp in herds that were members of a milk cooperative.
DESIGN: Epidemiologic study. SAMPLE POPULATION: 267 dairy herds that were members of a milk cooperative. PROCEDURE: Bulk-tank milk samples were collected monthly during a 6-year period from all dairies in the cooperative. Samples were submitted to the cooperative's laboratory for bacterial culture for Mycoplasma spp, using direct plating. Milk samples positive for Mycoplasma organisms were speciated.
RESULTS: Prevalence of positive samples varied from 1.8 to 5.8% for all species of Mycoplasma and from 1.2 to 3.1% for Mycoplasma spp known to be mastitis pathogens. One mycoplasmal species was isolated initially on 99 of 198 (50.0%) dairies, but 68 of 198 (34.3%) dairies had 2 species isolated. Mycoplasma bovis, M californicum, and M bovigenitalium were consistently isolated, but M bovis (243/499; 48.6%) was the most commonly isolated species. Acholeplasma laidlawii was more prevalent in 1989 and 1995 than other years. Mycoplasma bovigenitalium and M californicum had a seasonal distribution. Less than 50 colonies per plate were isolated for most (317/500; 63.4%) bulk-tank samples. Of the milk samples with > 100 colonies/plate, Mycoplasma bovis was isolated most frequently (73/243; 30.0%). CLINICAL IMPLICATIONS: Distribution of Mycoplasma spp varied by year, number of colonies isolated per sample, season, and herd. Therefore, it may be necessary to routinely sample bulk-tank milk, and all isolates should be speciated. Culture results from milk cooperatives should be used with other monitoring information to determine the Mycoplasma status of herds.