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.

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 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.
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