Dry cow treatments are effective in eliminating many Streptococcal bacteria infections in the dry period
Dry cow infections occur more frequently during the first few days of the dry cow period and the last few days of the dry cow period.
Dry periods are high risk periods for new infections
Blanket treatment versus selective treatment depends on local practices
2003 National Mastitis Conference
Ft. Worth Texas
A focus of the 2003 NMC meeting was management of mastitis during the dry period. In a pre-conference symposium several speakers detailed the status of dry cow mastitis management. It was clear that there are different strategies for managing this critical period depending on the country and region.
Dr. Ken Leslie, University of Guelph, Guelph, Ontario, Canada opened the session by reviewing the history as well as the current status of dry cow therapy (DCT). The use of high dose sustained release antibiotic treatments at dry-off is a 50 year old recommended practice that is still widely applied in many countries. The use of DCT at dry off is a key element of the current NMC recommended mastitis control program.
Dry cow treatments are effective (70-90%) in eliminating Streptococcal bacteria infections that may be present during the early dry period. They are much less effective against infections caused by Staph aureus or gram-negative organisms such as the coliforms. As cows approach calving, 45-60 days post dry-off, the antibiotic protective effect is gone and so no protection is provided by DCT during this critical period. Other approaches will have to be implemented to help reduce pre-calving new infections.
In certain countries it is recommended that all quarters of all cows receive treatment at dry-off. Some infection free quarters are treated following this protocol. Concern about antibiotic resistance and the fact that many herds have a low prevalence of intramammary infections have caused the practice of blanket dry cow therapy to be challenged. On the other hand, comparative studies have demonstrated that cows treated in all four quarters produced more milk in subsequent lactations than cows treated in selective quarters and was overall more cost effective. Part of the economic advantage is associated with testing costs to determine the infection status of each quarter at dry-off. Currently there is no fast, accurate way to do so other than milk sampling and culturing and this adds significant cost.
Dry cow infections occur more frequently during the first and last 10 days of the dry period. The rate of new infections appears related to housing conditions, teat end condition and the formation or lack of formation of an intact teat keratin plug following dry off. Keratin plug formation has been assumed to always occur but new research has indicated a significant percentage of teats fail to form an effective teat canal plug for part or all of the dry period leaving such cows more susceptible to new infections. This has created an opportunity for research and product development in the area of teat sealant, both external and internal.
In countries where detailed quarter infection information is readily available, selective therapy is recommended. Such factors as antibiotic resistance, relatively low infection prevalence in many well managed herds, low somatic cell counts in herds, failure of teat plug formation, overall costs and the ineffectiveness of antibiotics near calving will make the dry cow period the focus of additional creative research.
The Nordic countries approach to dry cow management was presented by Dr. Torkel Ekman of the Swedish Dairy Association. These countries have very comprehensive animal health record keeping systems and data bases that allow dairymen and the attending veterinarian to know the quarter infection status of cows. In addition there is a strong sentiment to reserve antibiotic treatment to truly sick animals or infected quarters. The overall focus and emphasis of veterinarians and dairymen is preventing disease rather than treating sick animals.
The Nordic countries have small herds and a national somatic cell count limit of 400,000. They emphasize disease preventive measures and they have national policies regarding who can treat cows for mastitis and with what treatment drugs. There is also a trend toward more organic dairy farming.
The net result is that Norwegian, Swedish and Finnish dairies average very low somatic cell counts, dry treat quarters on a selective basis relying on culture work and infection status history and focus heavily on preventive approaches rather than wholesale treatment approaches. It appears to work well for them.
Dr. Elizabeth Berry of the Institute for Animal Health, Compton, UK reported on recent evaluations of dry cow strategies tried in several countries. Attempts to treat quarters, based on infection status, requires accurate and quick test methods to determine infection status of individual quarters. Bacteriological testing of milk samples remains the ”gold standard” for this but adds cost. Other tests such as somatic cell data are not sufficiently accurate to be used as the sole basis for treatment.
A US study indicated treating all quarters of all cows produced fewer new infections and better yields in the following lactation than cows that were not treated. An Australian study compared three treatment strategies. Treatment of all quarters, treatment only of quarters considered infected based on a NAGASE positive test and no treatment at all, were evaluated. Treatment, either selective or blanket treatment of all quarters at dry-off reduced new infections at calving and during the dry period. The comprehensive treatment of all quarters produced fewer new infections than selective therapy. Similar results have been reported from UK studies. Based on these results it was her conclusion that administering dry cow therapy at the cow level rather than quarter level would produce the best results.
Parenteral administration of antibiotics is recommended in several countries but Dr. Berry indicated there is little scientific evidence of improved efficacy compared to use of intramammary dry cow tubes alone.
Teat sealant, both internal and external, was reviewed. They have been shown to reduce new infections when applied at dry off. So long as the external sealant is present and intact it provides protection for the teat end. Internal teat sealant has also demonstrated an ability to reduce new infections. Studies from New Zealand and the UK have provided evidence that the internal sealant can reduce new infections significantly, especially against the environmental Streptococci.
Dr. Hank Hogeveen of the Netherlands discussed a technique to model the costs and effects of various dry cow therapies. Using data from various studies and entering default values for issues such as intramammary infection percentages at dry off, cure rate for product used, new infections occurring during the dry period, a model can be built that simulates dry cow management and possible outcomes from implementing various treatment strategies. The outcomes can be expressed in economic terms. The model is only as accurate as the values used for each decision point but when such values are in line with actual empirical data, outcomes can be quite accurate. It allows various “what if” scenarios to be evaluated.
William Meaney of Teagasc Research Center, Moorepark, Ireland presented the final session of the pre-conference symposium. Their focus for some time has been development of an internal teat sealing material that could plug the teat canal from the inside. Several studies have shown that the internal teat seal performed effectively when used in herds that had relatively low levels of contagious pathogen contamination and needed protection mainly against environmental bacteria. The material used in the internal sealant is an inert material, bismuth sub-nitrate, and it is in the form of a paste. It is packaged in a plastet similar to a dry cow tube. After infusion through the streak canal it settles into the canal plugging it. At calving the material can be removed by applying sufficient pressure to the teat and squirting it out. Small flakes of residual material may be shed for several days after removal but this has not posed a milk quality concern.
The current material contains no antibiotic and has no ability to treat existing infections or prevent introduced bacteria at infusion from developing into new infections. Teat cleanliness at time of use is critical in order to prevent transfer of pathogens into the teat. Meaney and co-workers are also researching a “natural” anti-bacterial agent that could be infused prior to insertion of the sealant.
The objective is to provide non-antibiotic alternatives for the treatment and prevention of new infections during the dry period. This would reduce the risks associated with traditional antibiotics such as contaminated milk, bacterial resistance etc.
In summary the symposium presenters indicated the dry period is a high-risk period for new infections. Blanket dry cow therapy at dry off still has advantages in many countries while selective treatment appears to work well in areas where detailed quarter infection history is well known. Modeling techniques may allow various dry cow management strategies to be assessed before actually using them and in the future teat sealant will likely be a part of recommended dry cow management practices.