Take the Blanket Off
How to Determine which Method of Dry Cow Therapy is Right for Your Herd and Tips for a Successful Dry Period
Mastitis has been the leading cause of production losses on dairy farms for decades. The 5 Point Mastitis Control Plan, initially developed in the 1960’s, has made huge strides in improving hygiene measures to control the disease. This has resulted in a reduction in cases of mastitis caused by contagious pathogens, however this void has been filled with an increase in environmentally transmitted pathogens1.
This shift, coupled with the increasing pressure on all livestock farmers to reduce the use of antibiotics, has instigated the revision of dry cow treatment protocols. In 2012, 88% of Canadian herds and 72% of American herds reported implementing comprehensive or “blanket” dry cow therapy (BDCT)2. Dry cow therapy (DCT) is the leading cause of antibiotic use on dairy farms and it is estimated that at least 4 metric tons were used in the year 20003.
Recent studies evaluating the benefits of selective dry cow therapy (SDCT) have been generating positive results. By 2007, 11% of dairies in the Netherlands were already implementing SDCT4 and the protocol has been gaining popularity in the UK and Europe. In the past, the limiting factor against using this method was the lack of cost-effective screening tools5, but with the expansion of portable and in-house testing devices this factor is no longer a concern.
The Dry Period & Effects of Mastitis
The dry period is a critical point in the lactation cycle and therefore requires careful management. Treating cows for mastitis during the dry period is generally more effective and economic than during lactation since there is no antibiotic treated milk that needs to be discarded or withheld from the bulk tank. Although there is the opportunity to achieve high cure rates in the mid-dry period due to the lack of milk as a bacterial growth medium, there can also be a higher risk of developing new infections in the early and late dry period. In fact, the risk of developing a new infection is 20 times higher in the early dry period (or active involution stage)6.
This is due to increased pressure in the udder dilating the teat canal and making it easier for bacteria to penetrate, as well a change in housing and the absence of germicidal teat dipping at this time.
In addition to decreasing the production and quality of milk during lactation, mastitis has many negative effects on reproductive health7. Cows that calve with even a subclinical infection demonstrate decreased colostrum quality and yield, which negatively impacts calf health and growth. The presence of a subclinical infection also increases the risk of developing a clinical infection after calving by 25%-30% and results in decreased service-conception rates.
Blanket vs. Selective Dry Cow Therapy
In order to prevent these negative consequences of infection, the goal of the dry period is to effectively treat any infected quarters and prevent uninfected quarters from becoming infected. BDCT involves administering antibiotics to every quarter of every cow when they enter the dry period, regardless of whether or not they have either a subclinical or clinical infection. In the past, it was believed that antibiotics would have a prophylactic (preventative) effect on uninfected quarters, but this is now being called into question8.
If there is no benefit to using antibiotics to prevent infections, their use on some cows may do more harm than good. Administering antibiotics without the presence of infection creates selective pressure on the small population of pathogens that are present, allowing the stronger, more resistant organisms to survive and multiply9. One study found that treating low SCC cows with antibiotics at dry off increases the risk of gram-negative clinical infections during the next lactation10.
SDCT aims to identify and treat with antibiotics only the cows in the herd that need it due to the presence of a clinical or subclinical infection. A large part of this method also involves increased identification of the causal pathogen in order to target treatment more effectively; not all antibiotics are indicated for use in all pathogen species. Any quarters that are not treated for infection will have a teat sealant applied in order to prevent new infections from developing.
One herd in the UK reported that 9 months after implementing SDCT, herd infection rate due to Staphylococcus aureus went from between 23%-27% to 16%11. A cure rate of 80% for chronically high cows was achieved and 90% of the herd now enters and exits the dry period with a low SCC compared to the previous 67%. These effects have resulted in the bulk tank SCC decreasing from 200,000 cells/mL to 160,000 cells/mL.
Separate studies by researchers in the U.S., Holland and Canada have concluded that when SDCT is used in appropriate herds there is no adverse effect on general udder health or milk yield and antibiotic use as well as treatment cost is reduced12. However, when applied in herds that are not appropriate for this treatment plan, although antibiotic use can decrease by as much as 85%, the incidence of clinical mastitis cases will also increase.
Criteria for Selective Dry Cow Therapy
With the increasing use of robotic milking machines and other technology that delivers personalized care to each cow, it is only rational that whenever possible, each cow’s dry period should be managed on an individual basis. As already mentioned, SDCT is not appropriate for every herd, so how do you know if your herd might be suitable?
Things that should be considered when considering SDCT are your herd’s current infection status, your hygiene practices at drying off, whether you plan to treat on the cow or quarter level, the average dry period length and your monitoring capability (which will also depend on your herd size)13.
Guidelines between countries vary regarding SCC thresholds based on industry regulations, but the general consensus is that for your herd to be suitable for SDCT, herd prevalence of subclinical infections must be under control. In North America, a bulk tank SCC under 250,000 cells/mL is a good threshold to determine herd suitability.
The most important factors to consider regarding practical application of dry cow therapy are hygiene practices and monitoring capability. Since not every cow or quarter may be receiving antibiotics, it is vital that new infections are not introduced when drying off, this will be discussed in more detail in the next section. You must also have the appropriate tools to accurately select which cows will receive antibiotics.
Selection methods could include 90-day cow health records (provided they are regularly updated and accurate), quarter culturing/PCR testing or in parlor CMT/SCC tests14. In parlor, SCC tests are the most accurate and efficient method of determining cow suitability. It is also advisable to determine the causative pathogen for any infected quarters, either through in parlor tests or lab culturing (although this method will take longer to receive results).
Cows that are selected for antibiotic treatment should have no history of clinical infection within the last 90 days and at the time of dry off should have an SCC under 200,000 cells/mL or a CMT score of 2 or less15. You may choose to treat only the quarters that do not meet these criteria or to treat the whole udder if one quarter does not meet the criteria.
If the SCC is over 200,000 cells/mL and there has been more than 1 clinical infection in the last 90 days, it is recommended that the whole udder receives antibiotic treatment. In addition, some researchers have recommended using different SCC criteria for primiparous and multiparous cows entering the dry period; under 150,000 cells/mL and under 200,000 cells/mL respectively16.
Tips for a Successful Dry Period
Care must be taken not to introduce bacteria into the teat canal when administering dry cow therapy. This can be done by:
- Using only one intramammary infusion tube per quarter
- Using a clean pair of gloves for each cow
- Using the partial insertion method to avoid damaging the keratin plug and pushing any pathogens present further into the teat cistern
- Dedicating a specific time and area for drying cows off to avoid introducing environmental pathogens from milking equipment, airborne particles etc17
If pathogens are introduced into a quarter while teat sealant is being applied, there is no way for those organisms to be shed and they will multiply throughout the dry period, causing high SCC and infection.
Select antibiotics based on causal pathogen
This will increase treatment efficacy and efficiency as well as reducing the chance of resistant strains developing.
House dry cows away from the milking parlor (especially during the early dry period)18
This will avoid any milk let down response, which can increase susceptibility to mastitis due to the presence of a growth medium for bacteria.
Always consult your veterinarian
You should always seek professional advice when considering switching to a new management program. This is especially critical when it comes to dry cow management since it is such a high-risk period for mastitis.
It is also important to work with your nutritionist to develop an effective transition diet.
The dry period is a critical time for mastitis management and prevention. Many industries are being encouraged to reduce antibiotic use, and Selective Dry Cow Therapy is the direction that many farms worldwide are going.
To determine if your herd is a good fit for this program, consider your average BTSCC and your records/testing capability. Cows and quarters that are selected for treatment should be based on clinical mastitis records and current SCC data. When used in appropriate herds in consultation with your veterinarians and other professionals, SDCT can decrease your herd’s antibiotic usage, treatment costs and the pain of mastitis.
About the Author
Anna Schwanke is an undergraduate student at the University of Guelph, Ontario. She is responsible for researching and writing about a wide variety of topics related to dairy cow welfare and management for Dairy Quality Inc. The 10 years she spent living in Australia, as well as her love of travelling, give her a firsthand viewpoint of issues facing the international dairy community. She plans to graduate from the University’s College of Physical & Engineering Science in 2019 and pursue a career in the Life Sciences or Agriculture industry.
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