I recently had a dairy producer call me with a question. In an effort to reduce expenses, he was reviewing his dry cow program. A fellow producer had suggested "splitting” dry cow tubes—using one tube per cow instead of one tube per quarter. I responded that in my experience, this is one of those situations where cutting costs can easily result in a milk quality disaster.
The strategy of splitting an antibiotic preparation that is packaged for individual use comes with a number of significant risks. The first is a basic sanitation issue.
Using the same tip to treat multiple teats, even if you have sanitized the teat ends with alcohol, increases the chances of carrying bacteria into the teat and udder when you treat. Practical experience tells me that the most likely and common way that new infections are created at dryoff is by using poor treatment technique. It doesn't matter that you are infusing antibiotics: If you are carrying bacteria into the teat when you treat, you will frequently create a new infection.
The other concern
with splitting single-use medications is that you are altering the dosage. These preparations are designed to deliver a certain level of antibiotic and to have it be present in the target tissue at or above a certain concentration for a certain period of time.
In theory, each type of bacteria reacts differently to a given antibiotic. In a laboratory setting, bacteriologists establish what is called a minimum inhibitory concentration (MIC), which is the threshold level of antibiotic that needs to be present to inhibit the growth of a particular bacterial strain.
The suggested dosage for an antibiotic is established by calculating the amount needed to provide levels above a target MIC level for a certain time. Once an antibiotic is administered, the body begins to eliminate or break down the product.
How long the drug is actually in the animal's tissue at or above the critical level depends on the balance of initial dosage and how fast it is eliminated. In other words, it is not just the level of antibiotic that is important, but also the duration that it is above the critical MIC level in the animal's tissue.
Reducing the dosage for a dry cow antibiotic might still deliver adequate initial levels. But the time that it is in the tissue at a level that will affect bacteria will be significantly shortened. Undoubtedly, this will have a meaningful impact on cure rates.
Finally, there is some evidence to suggest that you increase the risk of creating resistant strains of bacteria when you dose at levels below those intended.
When attempting to reduce the expense associated with antibiotic usage, it is probably more to the point to try to focus usage on those animals that truly need it and have a reasonable likelihood of a positive response. One needs to be cautious working through treatment strategies.
Many times, we can cut antibiotic usage significantly and still obtain the same or better results on a herd basis. For example, repeatedly treating chronic mastitis during lactation is a poor investment versus treating affected animals during the dry period.
In the case of the dry treatment, one alternative might be to go to a selective treatment strategy at dryoff. Most research still indicates that blanket dry cow therapy is generally the most economically effective strategy.
Yet there is some evidence that if you can determine at dryoff which cows have infected glands and which are uninfected, you can focus your treatment on those that are infected.
The trick, of course, is accurately identifying uninfected animals. To do so, you need to be working with a herd that has low levels of subclinically infected animals, and you need to be able to establish each cow's udder health status at dryoff.
You probably need to make sure that they are being dried off to a relatively clean environment. And you need to closely watch your fresh cows to ensure that the strategy is working.
"Mastitis Prevention Strategies For The Dry Period"
by Ken Leslie, University of Guelph, Guelph, Ontario, Canada