Research Study

Veterinary Medicine
Controlling mastitis with an aerosol teat disinfectant

These investigators felt there were too many problems associated with dip cup immersion methods of teat disinfection, so they decided to test the efficacy of an aerosol disinfectant.

MASTITIS, the most thoroughly investigated disease of dairy cattle, is also the most costly disease of American agriculture.^1,2 Nearly all mastitis infections result when pathogenic bacteria invade the streak canal and infect the mammary gland. Closing the canal will bar the entry of pathogens,^3,4 but there are other control measures as well that are highly effective when properly and persistently implemented. Proper post milking teat disinfection, for example, is foremost among them.^1,5 Surveys indicate that at least 20 to 30% of dairy farmers, however, still do not follow this practice.^6-10

Postmilking teat disinfectants usually are applied by immersing the cow's teat in a dip cup. Under controlled experimental conditions, this method reduces the incidence of new intramammary infections. Several problems, however, are inherent in this procedure.

For one thing, the average dairy farm is not operated under controlled experimental conditions, and infection may be spread via the dip cup. A cup that starts out clean at the beginning of milking is often visibly contaminated by the end of the milking. Hair, bedding, manure or other environmental debris may contaminate it.

When up to 40% of the cows in a herd display some degree of mastitis,^1,4,11,12 it's probably not a good idea to use one device that touches all of those teats. When the dip cup is not actually filled with disinfectant, it may touch and contaminate the teats without properly disinfecting them. Contamination of teat dip solution and dipping cups has been shown to cause serious outbreaks of mastitis.¹³

An alternative to dipping is the use of an aerosol spray teat disinfectant. Although the efficacy of spraying has been questioned, controlled experiments have show that the method of application (spray or dip) does not affect the efficacy of the teat disinfectant.¹⁶

Under conditions found on the farm, spraying may even have advantages over dipping. Sprayers can be more sanitary; only the spray touches the cow. Contamination of the disinfectant or spread of infection from cow to cow by the sprayer is less likely than with a dip cup. There is less risk of waste with spraying because there are no spills, so product should last longer. And unlike dips, sprayers are not messy to use.

The use of hand-pump sprayers not designed for spraying bovine teats, however, can cause problems. The horizontally directed spray may not give good coverage.¹⁵ Unfortunately, hand-pumps are probably the most common type of sprayers used on the farm.

Piped in wands to direct the spray vertically for better teat coverage are available, although their connections through tubes to a large pressurized tank make these units inconvenient to use in stanchion barns.

We conducted the following experiment to evaluate the effectiveness of an aerosol spray teat disinfectant containing chlorhexidine by comparing it to a similar teat disinfectant applied with a dip cup. The incidence of new intramammary infections under conditions of natural exposure was determined using methods similar to Protocol C of the National Mastitis Council.⁵

Experimental Design

The University of Connecticut dairy herd at Storrs was used for this study. The Holstein, Guernsey, and Jersey cows were housed in a stanchion barn and milked twice daily with bucket milkers. Rations consisted of hay, corn silage, and grain. The cows' bedding was kiln-dried sawdust. Postmilking teat disinfection and whole herd dry cow therapy were routine in this herd. The study lasted 17 months (April 1984 through August 1985). Quarter milk samples in 10 ml amounts were collected aseptically at the beginning of the study and monthly to bimonthly during the study.

Samples were analyzed by direct microscopic somatic cell count (SCC). For the purposes of our study, quarter milk samples with a SCC of less than 1.0 x 10⁶ were considered nonmastitic; samples with a SCC of 1.0 x 106 or higher were considered mastitic.^12,18

Quarters found to have SCC of 1.0 x 106 or higher before the study (based on the results of one test) were ineligible for new infection in this study. When an infection was diagnosed in a quarter, that quarter was ineligible for new infection during the remainder of that lactation. Quarter samples were collected for analysis before any treatment was administered to quarters that developed clinical signs of mastitis.

Samples with an elevated SCC also were analyzed by culture on blood agar and selective media. Bacterial isolates were identified by standard microbiological methods. ¹⁹ Staphylococcus aureus, esculin-positive streptococci, and coliform bacteria were the predominant organisms cultured from the herd before and during the study.

Cows were assigned to one of two treatment groups based on their DHIA computer control numbers. Cows with even DHIA numbers were treated immediately after milking with a dip cup containing a recognized effective commercial teat disinfectant containing 0.5% chlorhexidine and 4.9% glycerine (Nolvasan® Teat Dip - Fort Dodge) (Figure 1). This formulation is similar to other teat disinfectants considered effective in controlling mastitis.^4,5,11,20-22 Two dip cups were used and maintained in a sanitary condition. Dip cups were washed and filled with fresh teat disinfectant daily.

Immediately after milking, the teats of cows with odd DHIA numbers were treated with an aerosol spray disinfectant containing 0.4% chlorhexidine and 10% glycerine (Fight Bac® - Deep Valley Farm, Brooklyn, CT) (Figure 2). This teat disinfectant is packaged in a 15-oz * can with a water-soluble, non-fluorocarbon propellant and vertical spray nozzle. The propellant rapidly vaporizes on release from the pressurized can. The vaporization of the propellant from the disinfectant solution as it is sprayed onto the cow's teat increases the concentration of disinfectant on the teat (about 0.6% chlorhexidine and 15% glycerine).

* Note: Fight Bac® is now available in a 22-oz. can

The two groups were unbiased in milking order because they were evenly distributed throughout the milking line. The dip group contained 46 cows - 29 Holsteins, eight Jerseys, and nine Guernseys. The aerosol spray group contained 51 cows - 33 Holsteins, 11 Jerseys, and seven Guernseys.

The age distribution in the dip group was:

• First lactation - 26.09%
• Second lactation - 32.61%
• Third lactation - 19.57%
• Fourth and later lactation - 21.74%

The age distribution in the aerosol spray group was:

• First lactation - 39.22%
• Second lactation - 25.49%
• Third lactation - 17.65%
• Fourth and later lactation - 17.65%

The randomized selection by DHIA computer control number resulted in an imbalance in lactation number between the treatment groups - a higher percentage of cows in the aerosol spray group were in their first lactation. Analysis of our data, however, shows equal numbers of infection in first lactation groups. The first lactation cows in the aerosol spray group had a lower infection rate than the dip group, but the difference was not statistically significant. No bias in results occurred from the imbalance of lactation number.

Interpreting the results

Table 1 shows the number and type of new intramammary infections from a study of 382 quarters monitored during the 17-month period. A total of 14.4% of the quarters in the dip group became infected with major pathogens (S. aureus, coliforms, and streptococci other than Streptococcus agalactiae (This herd was S. agalactiae free.); 10.5% of the quarters in the aerosol spray group became infected.

The aerosol spray group had 27.2% fewer new intramammary infections as compared with the infection rate in the dip group, but the difference is not statistically significant. Teat end condition of both groups was normal throughout the study. No evidence of teat irritation was noted in either treatment group.

The new method of teat disinfection was as effective as dip application in reducing the rate of intramammary infection. A chief reason for the failure of mastitis control on the dairy farm is poor compliance with recommended procedures. The aerosol spray method of teat disinfection provides an alternative method for applying teat disinfectant that many farmers find convenient. (About 50,000 cans of spray have been sold to date). This convenience may encourage more persistent use.

Nearly all intramammary infections result form pathogenic bacteria passing through the teat canal, and the diameter of this canal influences a cow's susceptibility to infection. The wider the diameter, the more likely the mammary gland will become infected. The progressive dilation of the teat canal that occurs with age may be a factor in the higher incidence of intramammary infections in older cows.^4,23

The vacuum created by machine milking leaves the streak canal relaxed or dilated for up to two hours after milking, so cows may be highly susceptible to infection at this time.^3,24-26 Elastic fibers and an involuntary smooth muscle sphincter keep the streak canal closed.^27,28

Dipping the teat in ice water (38°F) for 30 seconds after milking markedly increases contractile tension of the teat sphincter muscle. This increased tension lasts more than three minutes, and does not return to the baseline value within 15 minutes.²³ Chilling the teat, as well as disinfecting it after milking could help reduce intramammary infections.

The aerosol spray teat disinfectant tested in this study was developed with a non-fluorocarbon propellant system that delivers the active ingredient to the teat at a temperature of about 34°F. The effect of briefly chilling the teat may be an addition benefit, but this needs further study. Also, although our study showed that the two products were equally effective, an additional research topic might be the effect of glycerin content on product efficacy.

Acknowledgment - The authors express their thanks to Sam Shepherdson of the University of Connecticut for his technical assistance, and to J. Woodrow Pankey of the University of Vermont for his evaluation of the manuscript and recommendations.

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Unpublished Study – Dr. Ken Leslie, Dr. Don Barnum, Anna Dashiri, Johnathon McTaggart: Ontario Veterinary College, Ontario, Canada. November 1996 study, adhering to National Mastitis Council protocol, showed 96% reduction in mastitis.