Isolation of multiple Salmonella serovars from a dairy two years after a clinical salmonellosis outbreak

Samples were obtained for bacteriologic culturing of salmonellae from cows and calves on, and the environment of, a large California dairy that used free-stall housing and a flush system for manure handling. Two years previously, the dairy had an outbreak of clinical salmonellosis in the lactating herd; however, since that time, it had not had problems with clinical salmonellosis. On the basis of mean annual milk production per cow, this dairy was consistently ranked in the top 25% of dairies in the area enrolled in the Dairy Herd Improvement Association. Results of bacteriologic culture of 76% (108/142) of environmental samples and 48% (639/1,339) of fecal samples were positive for salmonellae. Eighty-two percent of the isolates were serovar C1, subclassified as Salmonella montevideo, and 17% were serovar E. Results of bacteriologic culture of 85% of samples of recycled flush water being pumped into the free-stall alleys were positive, as were results of bacteriologic culture of 78% of samples of herd bulk milk filters, 97% of fecal samples collected from calves being fed nonsalable milk, and 25% of fecal samples collected from cows at the time of breeding. These findings suggest that freedom from clinical salmonellosis and comparatively high measures of herd performance do not indicate the absence of salmonellae from a premises, and that hardy infectious agents transmitted by ingestion of feces can become established in the environment of modern free-stall dairies that use recycled water in their manure flush systems.