Intercept-only random effects and single-fixed-variable mixed-effect REML models of loge concentration of total and ampicillin-resistant E. coli (to ≥8 mg/liter) in fecal samples collected from organic table chickens

VariableTotal E. coli concnAmpicillin-resistant E. coli concn
Variance (σ2)Coefficient (β)95% CIP valueVariance (σ2)Coefficient (β)95% CIP value
Random effects (intercept-only models)
    Bird0.0003 1.23
    Within bird over time 3.55 a 3.68
    Fecal dilution series0.00030.00002
    Dilution plated0.050.07
    Sample aliquot (residual)0.060.06
Fixed effects (single-fixed-variable models)
    Age of bird (days)0.02−0.03-0.060.44 0.06 0.03-0.09 0.0008
    Weight of bird (kg)0.12−0.53-0.780.71 1.05 0.50-1.59 0.0003
    Sex of bird
    Source of sample
        Pet carrierRefRef
        House floor/field−0.41−1.31-0.480.360.13−0.89-1.140.81
    Fecal color
        Dark brownRefRef
        Light brown0.43−0.55-1.420.39−0.22−1.28-0.850.69
    Fecal consistency
        Well formedRefRef
    Fecal volume
        Scanty−0.78−1.64-0.080.08 −1.33 −2.23-−0.42 0.005
  • a The numbers reported in bold indicate marked effects (variance > 1 and P = 0.05).

  • b Ref indicates the reference category for that variable.