OUR INDUSTRY TODAY Efficacy of Chlorhexidine as a Postmilking Teat Disinfectant for the Prevention of Bovine Mastitis During Lactation s. P. OLIVER: s. H. KING, M. J. LEWIS, P. M. TORRE, K. R. MATTHEWS, and H. H. DOWLEN Department of Animal science Instilute of Agriculture University of Tennessee Knoxville 37901-1071 ABSTRACT 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 experi- mental 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, pri- marily Streptococcus uberis and Strep- tococcus dysgalactiae. New infections by Streptococcus species were significantly lower in teats dipped in chloxbexidine than in undipped teats. Overall efficacy of the chlorhexidine teat dip against major mastitis pathogens was 50%. The experi- mental teat dip also reduced coagulase- negative Staphylococcus species infec- tions 49.0% and Corynebacterium bovis infections 65.2%. Overall efficacy against minor mastitis pathogens was 54.0%. No hitation or chapping of teats dipped in the experimental teat dip was observed. (Key words: intramammary infection, postmilking teat dip, chlorhexidine) INTRODUCTION Postmilking teat disinfection is one of the most effective procedures for reducing the rate of subclinical and clinical mastitis during lacta- Received December 18,1989. Accepted February 26,1990. 'Reprint requests. tion (1, 10, 17). Teat dipping has been recom- mended widely by dairy advisors and adopted by dairy producers in increasing numbers be- cause the method is recognized as simple, eco- nomical, and effective in controlling mastitis. Despite universal acceptance of teat dipping as a method of mastitis control, limitations are associated with most teat dips currently avail- able. The most significant limitation is that teat dips do not afford equal protection against the vast array of bacteria that cause mastitis (1, 2, 3, 18, 21). Although teat dipping effectively reduces intramammary infections 0 caused by Streptococcus agalactiae and Staphylococ- cus aureus (1, 17), it has not been effective in controlling mastitis caused by environmental pathogens such as coliforms and streptococci other than Strep. agalactiae (1, 2, 3, 13, 21, 22). Iieffectiveness of postmilking teat dips in prevention of mastitis by environmental patho- gens is thought to be dated to differences in the reservoir of mastitis pathogens and to the time when bacterial exposure takes place (1, 22,23). The primary reservoir of Strep. agalac- tiae and Staph. aureus in dajl herds is thought to be infected mammary glands (21,23). Expo- sure to contagious pathogens occurs during the milking process when milk containing bacteria, contaminated hands, or contaminated milking machine liners come in contact with teats of uninfected mammary glands. Postmilking teat disinfection kills bacteria transferred to teats during milking, thus decreasing IMI due to Strep. agalactkae and Staph. aureus. Reservoirs of environmental mastitis pathogens are not only infected mammary glands but also the environment. Teat dipping reduces the number of environmental pathogens on teat skin imme- diately after milking. However, exposure of teats to environmental pathogens continues be- tween milkings when most teat dips have lost 1990 J Dairy Sci 73:2230-2235 2230