Choosing the right teat dip for your farm can be an overwhelming process. There are several germicides in varying concentrations available in the market today. When choosing a teat dip, however, it is important to remember the dip’s most important job: killing organisms that can cause mastitis.
With that in mind, it is extremely important to buy a dip with known germicidal properties. This is why most teat dip manufacturers have a method to evaluate teat dips for efficacy.
The National Mastitis Council currently recommends the following protocols for testing teat dips: efficacy of a post-milking teat dip after experimental exposure of teats to mastitis, efficacy of a post-milking teat dip based on reduction of naturally occurring new intramammary infections (uses a negative control), comparing an experimental post-milking teat dip with a product of known efficacy based on incidence of naturally occurring new intramammary infections (uses a positive control).
There have been many teat dips evaluated under the three protocols mentioned above. These protocols are the gold standard when evaluating teat dip efficacy. These methods of testing teat dips will yield the most reliable results, without question.
You will notice, however, all three protocols require the work be done on-farm and on live animals. The use of live animals can become very expensive and labor-intensive. It can also be difficult to find a private farm or university farm willing to expose their animals to mastitis-causing pathogens, as is necessary for the first protocol.
These studies can also take extended periods of time to complete. In light of these issues, most manufacturers have sought alternate methods to evaluate effectiveness of their teat dip. While these alternate methods give us some indication of the germicidal activity in the dip, it is important to remember there is no replacement for a “real world” trial. That is a study done on a farm in real conditions on real, lactating cows.
Because a lab-based method of testing the germicidal activity of a teat dip is better than not testing the germicidal activity at all, we will outline some of the methods that may be used by teat dip manufacturers.
One test method used by several major teat dip manufacturers is commonly referred to as the AOAC. The AOAC actually stands for Association of Analytical Communities. This organization is an international, non-profit scientific association. It publishes standardized, chemical analysis methods designed to increase confidence in results of chemical and microbiologic analyses.
The test most commonly used with teat dips is the AOAC Method 960.09 Germicidal and Detergent Sanitizing Action of Disinfectants. In this method, a sample of the disinfectant is inoculated with a suspension of a representative test organism. Following a 30-second exposure, the sample is neutralized and quantitatively assayed for bacterial survivors.
The resulting plates are incubated, the number of survivors is enumerated, and a percent and log10 reduction is determined as compared to a population control. In order to successfully demonstrate sanitizing efficacy, the product must demonstrate a 99.999 percent (or 5 log10) reduction. All of the most common mastitis-causing organisms can be evaluated using this method.
Another method being utilized is called the EN 1656. This test is a standard test utilized in Europe. It is very similar to the AOAC. The bacteria are exposed in suspension to the teat dip being evaluated. The main difference is: This test uses an “interfering substance” (usually milk) when the bacteria is exposed to the teat dip being tested.
Following the exposure time (15 seconds, 30 seconds, etc.), the teat dip is neutralized and assayed for bacterial survivors much like the AOAC test.
When looking at data from these two tests, it is important you take note of the organisms being tested. It is prudent to be sure the teat dip in question will kill bacteria that are known mastitis-causing pathogens. In addition to this, if you know you have a mycoplasma problem, you should search for a dip that has been tested against mycoplasma.
Also note the contact time, that is, the time allowed for the dip to kill organisms before the active ingredient in the dip was neutralized. If the dip took 45 seconds to achieve 99.999 percent kill, and your pre-dip is only on your cows’ teats for 30 seconds, you may want to look for a teat dip with a quicker kill.
Finally, some manufacturers use an excised teat protocol. This method involves collecting teats from slaughtered cows, freezing them and transporting them to the lab. Teats are generally cleaned extensively and frozen until they are ready to be used. A broth of pathogens is then created, and the teats are dipped in the broth once they are defrosted and cleaned again. The teats then “drain” for a period of time.
After draining, the teats are dipped in the teat dip to be tested. After the teats are dipped, the organisms are removed by rinsing the teat, plated on agar, incubated – and finally any bacteria that may be present are counted. It is important to note these results are compared to control teats dipped into the pathogen broth but not dipped with the teat dip product.
This article is not an all-inclusive review of lab-based methods of testing teat dips. It is meant to give a quick review and a very basic understanding of some of the testing methods major teat dip manufacturers may use other than on-farm trials. Manufacturers also may use a combination of these methods.
Research studies conducted on-farm utilizing live, lactating cows will always be the most reliable way to evaluate teat dip products. But these lab-based tests do provide us with some useful information and are certainly better than not testing a teat dip at all. When choosing a teat dip for your farm, you should ask how the teat dip was tested to ensure you are receiving a product with known germicidal activity.
