title: Evaluation of stocking density and subtherapeutic chlortetracycline on Salmonella enterica subsp. enterica shedding in growing swine.
abstract: The objective of this research was to determine the effect of stocking density and inclusion of subtherapeutic chlortetracycline in the diet on Salmonella fecal prevalence and antimicrobial resistance in growing swine. A 2 x 2 factorial design was employed on a privately owned commercial swine farm. Four finisher rooms were included in the study. Two of the rooms received 50 g/tonnes of chlortetracycline in the ration, two rooms received no antimicrobials in the feed. In each room, alternate pens were assigned to either high stocking density (0.60 m2/pig) or low stocking density (0.74 m2/pig). Pigs were placed in the finisher rooms at 10 weeks of age and followed for 6 weeks. Individual fecal samples were collected from the floors of each pen and cultured once weekly. Antimicrobial resistance phenotypes were determined. Data were analyzed using multilevel, multivariable logistic regression. Pigs fed chlortetracycline were at increased odds (OR 6.88, 95% CI 2.77-17.12) to shed Salmonellae. No other associations between treatments (CTC and stocking density) and Salmonella prevalence or reduced susceptibility to antimicrobials were identified. Variance in the odds of a fecal sample to be positive was distributed mostly at the lowest level, the individual fecal sample. The increased risk of shedding associated with inclusion of subtherapeutic chlortetracycline in swine diets is discordant with previous results by our group, suggesting farm or strain specific factors may impact this association. Understanding this risk may provide a potential intervention for controlling Salmonella pre-harvest.
authors.affiliation: Large Animal Clinical Sciences and the National Food Safety & Toxicology Center, College of Veterinary Medicine, Michigan State University, 165 Food Safety & Toxicology Building, East Lansing, MI 48821, USA. funkj@cvm.msu.edu
authors.forename: Julie
authors.initials: J
authors.lastname: Funk
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Wittum
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: LeJeune
authors.forename: Päivi J
authors.initials: PJ
authors.lastname: Rajala-Schultz
authors.forename: Andrew
authors.initials: A
authors.lastname: Bowman
authors.forename: Andrew
authors.initials: A
authors.lastname: Mack
mesh_terms: D000821:Animal Feed; D000822:Animal Husbandry / Q000379:methods*; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology / Q000627:therapeutic use*; D002751:Chlortetracycline / Q000494:pharmacology / Q000627:therapeutic use*; D015169:Colony Count, Microbial / Q000662:veterinary; D016001:Confidence Intervals; D024881:Drug Resistance, Bacterial; D005243:Feces / Q000382:microbiology; D005260:Female; D016015:Logistic Models; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D015999:Multivariate Analysis; D016017:Odds Ratio; D011156:Population Density; D011897:Random Allocation; D012481:Salmonella Infections, Animal / Q000382:microbiology / Q000517:prevention & control*; D019779:Salmonella enterica / Q000187:drug effects* / Q000302:isolation & purification; D013552:Swine / Q000254:growth & development; D013553:Swine Diseases / Q000382:microbiology / Q000517:prevention & control*
chemical_list: D000900:Anti-Bacterial Agents; D002751:Chlortetracycline