Fecal shedding of, antimicrobial resistance in, and serologic response to Salmonella Typhimurium in dairy calves.

Abstract

OBJECTIVE: To determine the duration of fecal shedding of and serologic response to Salmonella spp after natural infection in dairy calves and characterize Salmonella organisms recovered from these herds. DESIGN: Longitudinal study. ANIMALS: Calves from 2 dairy herds (A and B) in the northeast United States that were identified at the beginning of a Salmonella outbreak. PROCEDURES: Fecal samples were collected twice per week (herd A) or once per week (herd B); blood samples were collected for serologic testing once per week in both herds. Bacteriologic culture of fecal samples was performed, and Salmonella isolates were characterized by serotype, pulsed-field gel electrophoresis (PFGE) pattern, and antimicrobial resistance profile. RESULTS: All Salmonella isolates from herd A were serovar Typhimurium var Copenhagen, had the same PFGE pattern, and were resistant to at least 9 antimicrobials. All isolates from herd B were Salmonella Typhimurium, represented 2 PFGE patterns, and were susceptible to all antimicrobials evaluated. The estimated duration of fecal shedding was 14 days in herd A and 9 days in herd B. Few calves were seropositive for antibody against Salmonella lipopolysaccharide within the first week after birth (0 of 20 in herd A and 13 of 79 in herd B) or seroconverted (6 in herd A and 4 in herd B). Fecal shedding was more common in calves that seroconverted, but overall, there was not a strong association between seropositivity and fecal shedding of Salmonella organisms. CONCLUSIONS AND CLINICAL RELEVANCE: Although the herds differed in serologic response and Salmonella subtype, the duration of fecal shedding among calves was similar between herds.