title: Prevalence and antimicrobial resistance patterns of Salmonella enterica in preweaned calves from dairies and calf ranches.
abstract: OBJECTIVE
  To evaluate serovar and antimicrobial resistance patterns of Salmonella enterica isolated from preweaned calves and identify management risk factors associated with fecal shedding of S enterica.
  
  
  METHODS
  Cohorts of 10 to 15 preweaned calves (1 to 84 days of age) on 26 dairies and 7 calf ranches and cross-sectional samples of preweaned calves on smaller farms.
  
  
  METHODS
  Calves were evaluated every 2 weeks during a 6-week period. Salmonella isolates obtained from rectal fecal swabs underwent antimicrobial susceptibility testing against 12 antimicrobials. Cluster analysis enabled description of antimicrobial susceptibility patterns. Calf, cohort, and farm risk factors associated with both the prevalence of S enterica and multiple-antimicrobial-resistant S enterica in preweaned calves were identified with repeated-measure logistic regression models.
  
  
  RESULTS
  Salmonella enterica was detected on > 50% of farms and in 7.5% of 3,686 fecal samples. Many isolates (33%) were resistant to multiple antimicrobials. Shedding of Salmonella spp was negatively associated with increasing calf age, herds being closed to incoming cattle, and antimicrobial supplementation of milk replacer; prophylactic antimicrobial treatment in day-old calves increased shedding. No association between farm management and presence of multiple-antimicrobial-resistant S enterica or between calving management and presence of S enterica in calves < or = 1 week old was detected.
  
  
  CONCLUSIONS
  In preweaned calves, the most important factors associated with decreased likelihood of fecal shedding of S enterica were the use of antimicrobial-supplemented milk replacer and maintenance of a closed herd. Infection with multiple-antimicrobial-resistant S enterica was not associated with antimicrobial administration.
authors.affiliation: Department of Population Health and Reproduction, Veterinary Medicine Teaching and Research Center, University of California, Tulare, CA 93274, USA.
authors.forename: Anna Catharina B
authors.initials: AC
authors.lastname: Berge
authors.forename: Dale A
authors.initials: DA
authors.lastname: Moore
authors.forename: William M
authors.initials: WM
authors.lastname: Sischo
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D000833:Animals, Suckling; D002140:California / Q000453:epidemiology; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology / Q000382:microbiology*; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D003612:Dairying; D024881:Drug Resistance, Bacterial; D005243:Feces / Q000382:microbiology; D005260:Female; D016015:Logistic Models; D008137:Longitudinal Studies; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D015995:Prevalence; D012307:Risk Factors; D012481:Salmonella Infections, Animal / Q000453:epidemiology / Q000382:microbiology*; D019779:Salmonella enterica / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification*; D011795:Surveys and Questionnaires