Use Teat Dips That Have Been Tested for Effectiveness

From the NMC Newsletter "Udder Topics", Vol. 17, No. 1, February 1994

Choosing an effective teat disinfectant for use in a mastitis control program is no easy task. Numerous products containing several different germicides are currently on the market. At this time, no U.S. governmental agency requires efficacy, safety or residue data on teat disinfectants prior to marketing. As a result, some commercially-marketed teat dips have been tested for their ability to reduce new intramammary infections, while others have not been tested at all.

A teat dip should be chosen based on research evidence demonstrating safety and efficacy. Many teat dip products are safe and effective and have research data supporting their claims. If manufacturers have conducted the appropriate studies, they will be more than willing to share results of teat dip safety and efficacy studies with potential customers. Teat dips that have not been evaluated should not be assumed to be safe and effective and should not be recommended. Furthermore, an effective postmilking teat dip should not be assumed to be safe and effective as a premilking teat dip.

Protocols for evaluating pre- and postmilking teat disinfectants have been developed by the National Mastitis Council. Teat dip manufacturers are encouraged to utilize NMC protocols for determining teat dip safety and efficacy. Protocols for postmilking teat dips (published in the Journal of Dairy Science, Vol. 73, No. 9, 1990, p. 2580) and premilking teat disinfectants (published in the NMC 1991 Annual Meeting Proceedings, p. 157) are summarized below.

Determining Efficacy of a Postmilking Teat Dip After Experimental Exposure of Teats to Mastitis Pathogens.
This protocol is also referred to as "Experimental Challenge". After milking, all teats of experimental cows are dipped in a bacterial suspension containing specific mastitis pathogens. The experimental teat dip is then applied to two teats of each udder immediately after exposure to the bacterial challenge suspension; the remaining teats are not dipped. Efficacy of the experimental teat dip is based on the reduction in rate of new intramammary infections (IMI) in dipped quarters as compared to rate among undipped (control) quarters.

Advantages of the Experimental Challenge protocol for evaluating teat dip efficacy are: 1) efficacy can be determined in a much shorter time, generally a few months, compared to natural exposure studies that require 12 months or more; 2) experimental conditions and experimental cows can be controlled and monitored more closely; and 3) effectiveness against a particular pathogen can be determined. Disadvantages of the Experimental Challenge protocol are: 1) studies need to be conducted in research herds; 2) efficacy is only determined against one or two pathogens; and 3) it does not take into account herd management factors and seasonal variation in incidence of IMI.

Determining Efficacy of a Postmilking Teat Dip Based on Reduction of Naturally Occurring New Intramammary Infections.
Also referred to as "Natural Exposure", these studies can be conducted in commercial or research herds. At least two herds should be used and the trial should last at least 12 months. Experimental design can be either split-herd or split-udder. In a split-herd design, teats of half the cows are dipped in the experimental product immediately after machine removal, while the teats of remaining cows serve as undipped negative controls. In a split-udder design, two teats (diagonal or either side) of each udder are dipped in the experimental product immediately after machine removal; remaining teats are not dipped and serve as negative controls. Efficacy is based on the reduction in rate of new IMI in dipped quarters as compared to rate among undipped control quarters.

Advantages of the Natural Exposure protocol are: 1) it does not require a research herd to conduct the study; 2) the experimental teat dip is evaluated under more realistic conditions; 3) it takes into account stage of lactation and seasonal influences; and 4) data on a wider array of pathogens can be obtained. Disadvantages are: 1) it requires at least 12 months to obtain data; and 2) if commercial herds are used it may be difficult to control experimental procedures.

Comparing an Experimental Postmilking Teat Dip with a Product of Known Efficacy Based on Incidence of Naturally Occurring New Intramammary Infections.
This protocol is essentially the same as the Natural Exposure protocol previously described, except that a teat dip of known efficacy (a positive control) is used instead of no teat dip (negative control). For example, if a split-herd design is used, all teats of half the cows are dipped in the experimental product and teats of cows in the remaining half of the herd are dipped in a previously tested product and serve as positive controls. This type of study is advantageous when it is impractical to not dip cows' teats such as in commercial dairy herds, or if the purpose is to compare two teat dip products.

Determining Efficacy of a Premilking Teat Dip Based on Reduction of Naturally Occurring Infections.
Trials should be conducted in at least two herds for at least 12 months, using either a split-herd or split-udder design. Teats of all cows should be forestripped, washed and dried with single service paper towels prior to milking. Teats of cows in the treatment group are then dipped in the experimental product and dried thoroughly with a single service paper towel. A postmilking teat dip of known efficacy should be applied to all teats after milking. Efficacy of the experimental product is based on the reduction in new intramammary infection rate in predipped quarters compared to the rate among non-predipped quarters. (Note: currently there is not an NMC protocol for determining efficacy of a premilking teat disinfectant under experimental challenge conditions.)

Source: The Bovine Proceedings, No. 26, January, 1994, p. 79
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