Effect of double disinfectant application during premilking teat disinfection on teat cleanliness, bacterial count, and mastitis in pasture-grazed dairy cows

The use of double disinfectant application during premilking teat disinfection on heavily soiled teats has proven effective in reducing the teat cleanliness score and certain bacterial groups in freestall confined cows. We aimed to compare the efficacy of a single (SDA; before forestripping) and a double (DDA; before and after forestripping) disinfectant application on teat cleanliness score, bacterial counts, and the incidence of subclinical and clinical mastitis in pasture-grazed dairy cows. Initially, 2 groups of 8 cows were assigned to receive either SDA or DDA lactic acid and hydrogen peroxide application, using a dip cup. The treatments were applied at every milking to all lactating cows participating in the experiment. The experiment was conducted over an 8-mo period. Cows calving during this period were alternately assigned to one of the 2 groups after 7 d. Every 15 d, both before (PRE) and after (POST) treatment, we evaluated the teat cleanliness score (TCS) and collected swabs from teat skin to quantify gram-negative bacteria (coliform and noncoliform), <i>Staphylococcus</i> spp., <i>Streptococcus</i> spp., and total bacterial count (TBC). On the same day, we also collected milk samples from individual cows to measure SCC and identify subclinical mastitis (SCC ≥200,000 cells/mL). We then classified the cows as having no subclinical mastitis and new subclinical cases based on 2 consecutive analyses. Clinical mastitis cases were recorded throughout the experiment. A variance analysis was performed to evaluate the effect of treatment on bacterial count, TCS, and SCS. After disinfection, gram-negative and <i>Streptococcus</i> spp. were the most reduced type of bacteria regardless treatment. No significant differences were observed between the DDA and SDA groups for TCS, counts of coliforms, gram-negative noncoliform bacteria, <i>Staphylococcus</i> spp., <i>Streptococcus</i> spp., and TBC PRE and POST application or in reducing these variables. We transformed SCC into SCS, which was similar between groups, as well as the subclinical and clinical mastitis cases. In situations with lightly soiled teats, an extra application of disinfectant during premilking teat disinfection did not significantly improve TCS, reduce bacterial counts, SCS, or decrease the incidence of subclinical and clinical mastitis compared with a single application of disinfectant.