A natural exposure study was conducted for 14 months to evaluate efficacy of 0.25% iodine premilking teat disinfectant for the prevention of new intramammary infections. Predipping was compared with a negative control using a split-udder experimental design. All teats were dipped after milking with the same teat dip. Most new major pathogen intramammary infections resulted from Streptococcus species, primarily Streptococcus uberis and Streptococcus dysgalactiae, and from gram-negative bacteria, primarily Escherichia coli. New infections by gram-negative bacteria were significantly lower in quarters with teats predipped and postdipped than in quarters with teats postdipped only. Percentage of quarters newly infected by major mastitis pathogens was 48.6% lower in quarters with teats predipped and postdipped than in quarters with teats postdipped only. Statistical differences in incidence of clinical mastitis between treatment groups were not observed. Predipping and postdipping was no more effective against Staphylococcus species and Corynebacterium bovis than postdipping only. These data suggest that pre- and postdipping with the test product was more effective against major pathogens than postdipping only and provide additional evidence that premilking teat disinfection is an effective management procedure for prevention of environmental pathogen intramammary infections.

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