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

## TL;DR

This study found that applying disinfectant twice before milking doesn't improve teat cleanliness or reduce mastitis in cows with lightly dirty teats.

## Contribution

The study introduces evidence that double disinfectant application is unnecessary for lightly soiled teats in pasture-grazed dairy cows.

## Key findings

- No significant difference in teat cleanliness scores between single and double disinfectant applications.
- Double disinfectant application did not reduce bacterial counts or mastitis incidence compared to single application.
- Gram-negative and Streptococcus bacteria were most reduced regardless of disinfectant application method.

## Abstract

Summary: This study compares the efficacy of a single disinfectant application (SDA) and double disinfectant application (DDA) during premilking teat disinfection in relation to teat cleanliness, bacterial counts, and the incidence of subclinical and clinical mastitis in pasture-grazed dairy cows. On average, the cows had lightly dirty teats, leading to no significant difference in teat cleanliness scores and bacterial count reductions between the 2 treatments. The dynamics of clinical and subclinical mastitis were also similar between the 2 groups.

Summary: This study compares the efficacy of a single disinfectant application (SDA) and double disinfectant application (DDA) during premilking teat disinfection in relation to teat cleanliness, bacterial counts, and the incidence of subclinical and clinical mastitis in pasture-grazed dairy cows. On average, the cows had lightly dirty teats, leading to no significant difference in teat cleanliness scores and bacterial count reductions between the 2 treatments. The dynamics of clinical and subclinical mastitis were also similar between the 2 groups.

•Environmental conditions are conducive to lightly soiled teats before milking.•DDA is not necessary when cows have lightly soiled teats.•Clinical and subclinical mastitis dynamics were similar between treatments.

Environmental conditions are conducive to lightly soiled teats before milking.

DDA is not necessary when cows have lightly soiled teats.

Clinical and subclinical mastitis dynamics were similar between treatments.

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), Staphylococcus spp., Streptococcus 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 Streptococcus 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, Staphylococcus spp., Streptococcus 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.