This study compared the efficacy of betadine and chlorhexidine for drying off mammary quarters chronically infected with Staphylococcus aureus. Fourteen cows with chronic S. aureus infections in a single quarter were randomly assigned to treatment with either betadine or chlorhexidine. While betadine appeared to permanently cease lactation in treated quarters, S. aureus could still be cultured from these quarters later. In contrast, 71% of chlorhexidine treated quarters resumed lactation in the next period and over half cleared the S. aureus infection. Therefore, chlorhexidine may be a better option for therapeutic drying off as it allows for milk production while reducing the reservoir of infection.

1. A Comparison of Betadine and Chlorhexidine For Drying-Off Mammary
Quarters
Chronically Infected With Staphylococcus aureus
John R. Middleton and Larry K. Fox
Washington State University
Pullman, Washington
Introduction
A review of the current veterinary literature found only a single study evaluating
therapeutic dry-off of chronically infected mammary quarters (1). In that study the authors
used an infusion of chlorhexidine to cause cessation of lactation in chronically infected
mammary quarters. To date no studies have evaluated the ability of a therapeutically dried
mammary quarter to return to function in the subsequent lactation, nor has there been a
study to evaluate the efficacy of such a treatment in curing chronic intramammary
infections (IMIs). The purpose of the present study was to compare the ability of
chlorhexidine and betadine to cause cessation of lactation in the treated quarter, assess milk
production in the infused quarter in the subsequent lactation, and evaluate whether a
microbiological cure could be attained.
Materials and Methods
Fourteen cows from the Washington State University dairy herd were identified as having
chronic, single quarter Staphylococcus aureus IMIs. Chronicity of S. aureus IMI was
determined by monthly quarter milk cultures performed prior to this study (2). A persistent
infection was defined as 2 out of 3 positive cultures. Cows were randomly assigned to one
of two treatment groups, betadine or chlorhexidine, such that every other cow received
chlorhexidine. Treatments were intramammarily instilled in the S. aureus infected quarters.
Milk production from each mammary quarter (kg of milk/quarter) was measured from all
cows for five consecutive days prior to treatment. Quarter milk weights were measured
again at the beginning of the subsequent lactation for five consecutive days to assess return
to function of the treated quarter. All cows were pre-treated with 600 mg of flunixin
meglumine (Banamine, Schering Plough, Union, NJ) intramuscularly 15 minutes prior to
infusion of either betadine or chlorhexidine. Cows in the betadine group were infused with
120 ml of 5% povidone-iodine solution (0.5% iodine) after quarter milk weight
measurements on the fifth day. Chlorhexidine treated cows were infused with a proprietary
chlorhexidine suspension (Nolvasan suspension, Fort Dodge Animal Health, Fort Dodge,
IA) after two milkings 24 hours apart. Treated quarters in both groups of cows were not
milked for the rest of the lactation. Milk from treated cows was withheld from the bulk tank
for 96 hours post-infusion. All non-infected quarters were infused with a dry cow
intramammary antibiotic at the end of lactation. To assess whether a microbiologic cure had
been obtained, quarter milk samples were collected monthly for the first three months of
the subsequent lactation and cultured for S. aureus. Cows having three consecutive negative
milk cultures for S. aureus were classified as cured.

2. Mean milk production in each quarter and mean milk weight difference (MMWD = mean
milk weight (kg) in the uninfected contralateral control quarter - mean milk weight (kg) in
the infected quarter) were calculated from measurements made prior to treatment and in the
subsequent lactation for each cow. Student's t-test was used to assess for significant
differences in milk production between groups.
Results
Mean milk weights and milk weight differences are summarized in Table 1. None of the
cows in the betadine group produced milk in the treated quarter in the subsequent lactation,
whereas as 5 of 7 (71%) cows in the chlorhexidine group produced milk in the next
lactation. There was no significant difference in MMWD in the chlorhexidine group
(p>0.05) before treatment or in the next lactation, whereas the MMWD was greater after
treatment in the betadine group (p=0.0007). Microbiologic cures were obtained in 4 of 7
(57%) cows treated with chlorhexidine. No cures were obtained in the betadine group.
Table 1. Mean milk weights and milk weight differences in infected and control quarters
for cows
in each treatment group.
. Mean milk weight in kg by quarter
No. Cow Treatment Sample Period Infected Control Difference
7 Betadine Before Treatment 1.6 3.2 1.6
After Treatment 0.0 4.5 4.5
7 Chlorhexidine Before Treatment 2.3 2.5 0.3
After Treatment 1.9 3.3 1.4
Conclusions
This study suggests that chlorhexidine has potential as a method of therapeutic dry-off for
mammary quarters chronically infected with S. aureus. While betadine appears to cause
permanent cessation of lactation in the treated mammary quarter, S. aureus can still be
cultured from that quarter in the subsequent lactation. Hence, betadine treated quarters may
remain a reservoir for infection of herdmates. Conversely, 71% of the chlorhexidine treated
quarters returned to lactation and greater than 50% of chlorhexidine treated quarters
became S. aureus negative. Therefore, production can be obtained, while the reservoir of
infection is diminished.
References
1. Boddie RL, SC Nickerson. 1993. Permanent Drying Off of Chronic Mastitic Quarters.
Louisiana Cattlemen. Nov: pp. 10-11.
2. Middleton JR, LK Fox, T Smith, et al. 1996. Intervention strategies to reduce the

3. incidence and prevalence of Staphylococcus aureus mastitis in a dairy herd. Proceedings
91st Annual Meeting of the ADSA, Corvallis, OR P137:163.
Presented at the National Mastitis Council 38th Annual Meeting, February 14-17, 1999.
Published in the 1999 National Mastitis Council Annual Meeting Proceedings, pg. 231.
http://www.nmconline.org/