Evaluating teat dip quality - A U.S. buyer’s primer
There are various approaches to evaluating post-milking teat dips for efficacy
Information found on the label must include the active ingredient
Teat dip efficacy evaluation procedures have been guided for many years by the National Mastitis Council guidelines. These spell out the basic protocol, which bacteria species to use, how to allocate cows to treatment groups to eliminate bias and how to collect samples and handle the resulting data. Two basic approaches have been used for evaluating post-milking teat dips. The first or "experimental challenge study" has generally been conducted at a university facility under the direction of the university researcher. It involves a comparison of an experimental product against no product whatsoever or negative control. All teats of all cows are dipped routinely in a broth of mastitis pathogens (typically Strep ag and Staph aureus) which act as the experimental challenge. Then half the teats are dipped with the teat dip and the other half are not dipped at all. When the study is completed after sufficient numbers of new infections have developed, a statistical comparison of the two groups is made. The intent is to show how the treatment product(s) compared to the negative control in limiting the number of new infections.
For experimental challenge studies, a reduction in the new infection rate of at least 50% is generally expected in order to feel confident that the dip really was effective. In many studies reductions of 60-70% are seen. The reduction percentage is usually less for Strep ag than it is for Staph aureus. These results are reported by manufacturers in data cited for product efficacy.
Another approach involves the natural exposure study. This is run on commercial farms under the direction of a trained supervisor. Since most dairies will not allow "no dipping", these studies generally involve comparing a known, efficacious product against an experimental product. The groups are allocated to minimize bias and the cows are sampled approximately monthly to determine new infection development. Such studies often last 12 months because it takes that long for any meaningful differences to emerge. At the end, the statistics compare the two groups looking for differing rates of infection.
Natural exposure studies are favored by many because they are representative of real world conditions. Successful results may indicate a different efficacy level than is the case with challenge studies.
During the course of these trials teat skin condition is monitored in a general sense. The point is to observe if treatments impact teat skin condition as well as new infection rates.
The official protocols are published in the Journal of Dairy Science, 73:2580-2585, 1990. At the most recent NMC meeting there was discussion about the best way to test teat dip efficacy in the future. University based testing, for example, where cows are intentionally infected is becoming an issue of concern to many of the university test sites where animal care policies are in place. They may not be able to do such testing in the near future.
The active ingredient of a product has to be listed on the label of that product if it is to be sold. The label is supposed to represent the actual amount of the active ingredient in the product. With iodine products, the label statement for active ingredient is simply, "active ingredient iodine” with the percentage listed. For other actives, the label statement has to accurately describe what the specific material is and its concentration. Chlorhexidine products, since there are two forms available, usually state whether they contain chlorhexidine gluconate or chlorhexidine acetate and the appropriate percentage.
The emollient content is not as clear-cut in some cases. A label may state explicitly that it contains a certain percentage of particular emollient (example 10% glycerin). Alternatively some labels only list a certain percentage of emollients and not state exactly what emollients are.