In vitro and in vivo evaluation of a 0.5% chlorhexidine gluconate teat dip.

The activity of a 0.5% chlorhexidine gluconate postmilking teat germicide in reducing the numbers of Staphylococcus aureus and Streptococcus agalactiae on the skin of excised teats from cows was determined. The product yielded logarithmic reductions of 4.09 and 4.10 against S aureus and Str agalactiae, respectively, compared with 3.80 and 3.81 reductions, using a 1% iodophor dip. Germicide tolerance to an organic load containing Serratia marcescens or Pseudomonas spp was also determined. Organisms were not recovered from the product 8 hours after introduction of a simulated organic load containing either species of bacteria. The germicide was further evaluated against S aureus and Str agalactiae, using experimental challenge-exposure procedures in a research dairy herd. Efficacy was 73.4% (P less than 0.001) against S aureus and 68.1% (P less than 0.005) against Str agalactiae.