Feed contamination with Candida krusei as a probable source of mycotic mastitis in dairy cows.

Over 3 months, yeasts were isolated in pure culture from milk samples obtained from 8 lactating cows with acute mastitis and from 1 cow with subacute mastitis. Eight of the isolates were identified as Candida krusei; 1 isolate was not submitted for identification. The affected cows were assigned to separate milking groups and had not been treated by intramammary administration of antibiotic before the outbreak. Remission of disease without treatment was observed, followed by shedding of the yeast in milk for 2 to 5 weeks. Median somatic cell counts in the affected cows before, during, and 2 months after the onset of clinical signs were 93,000; 1,793,000; and 135,000 cells/ml, respectively. Wheat silage was found to be the probable source of the infecting microorganism, whereas inadequate milking hygiene resulted in its persistence in the herd. Following replacement of the silage and improvement of the milking hygiene, the outbreak ceased. Candida krusei thus may cause mastitis in cattle not only following intramammary antibiotic treatment, but also in conditions of heavy environmental contamination, in conjunction with inadequate milking hygiene.