Efficacy of chlorhexidine as a postmilking teat disinfectant for the prevention of bovine mastitis during lactation.

A natural exposure trial was conducted for 12 mo in a herd of 150 lactating Jersey cows to determine efficacy of a .35% chlorhexidine teat dip containing a glycerine emollient for the prevention of bovine intramammary infections. Right teats of cows were dipped in the experimental teat dip after milking machine removal and left teats were not dipped. The herd was free of Streptococcus agalactiae and had a low prevalence of Staphylococcus aureus. Most new major pathogen intramammary infections resulted from Streptococcus species, primarily Streptococcus uberis and Streptococcus dysgalactiae. New infections by Streptococcus species were significantly lower in teats dipped in chlorhexidine than in undipped teats. Overall efficacy of the chlorhexidine teat dip against major mastitis pathogens was 50%. The experimental teat dip also reduced coagulase-negative Staphylococcus species infections 49.0% and Corynebacterium bovis infections 65.2%. Overall efficacy against minor mastitis pathogens was 54.0%. No irritation or chapping of teats dipped in the experimental teat dip was observed.