Factors associated with variation in bulk-tank-milk Salmonella Dublin ELISA ODC% in dairy herds

Detection of Salmonella Dublin or Salmonella Typhimurium by bacteriological culture of individual faecal samples or of slurry samples was associated with higher bulk-tank-milk ELISA ODC%, as was apparent Salmonella prevalence, the mean ELISA ODC% or mean-yield-corrected ELISA ODC% in milk samples collected from all individual cows. However, combinations of risk factors that included number or prevalence of cows with a very high ELISA ODC% provided better models, indicating that the effect of the cow-level explanatory variables on the bulk-tank-milk ELISA ODC% was related to the activity of the infection in the herd. Barn type (loose housing or tie stalls) was not associated with the variation in bulk-tank-milk ELISA ODC% in these models, which might be useful in planning of surveillance programs and intervention strategies.