Why Selective Dry Cow Therapy (SDCT)?
Keep Mastitis and Somatic Cell Count (SCC) Low
Dairy farms around the world are shifting to selective dry cow therapy (SDCT) to improve the judicious use of antibiotics without compromising cow health or welfare. Mathijs Bakker, dairy veterinarian and consultant based in the Netherlands, has worked with many dairy farmers who have made the switch, and experience has told him that farmers can’t continue using the same blanket treatment protocols – even if it takes a higher level of management to keep mastitis and somatic cell count (SCC) levels low with SDCT.
Challenges of Selective Dry Cow Therapy
Important Factors for Success: Amount of Milk, Feed Rations, Separation Groups
“First, you have to reduce the amount of milk. In the Netherlands, we used to dry off cows at 20 liters (44 pounds) per day, and now we are advising farmers to dry off cows at 10 liters (22 pounds) per day,” he said. “Farmers need to change dry-off cows’ feed ration and move them to another group, particularly when working with a robotic milking system. It’s more labor and time to get dry-off cows from the robot to the separation group and, once a day, back to the robot. If a farmer isn’t willing to do this, SDCT can be a mess.”
Clean, Dry Bedding
Another important dry-off factor that farmers should consider is a cow’s bedding. Clean, dry bedding is extremely important to the success of the program, because bedding can act as a reservoir for some mastitis pathogens. Thus, replacing bedding often and reconsidering the source of bedding may also reduce bedding bacteria count. Farmers should work with their veterinarian to determine the best bedding source for their farm.
Internal Teat Sealant to Prevent Infections
Employee training to follow proper intramammary infusion technique.
Then, at the time of dry-off, farmers should use an internal teat sealant in all quarters to ensure cows don’t pick up an infection. Failure to follow a proper intramammary infusion technique can result in the introduction of mastitis pathogens to the udder. Well-trained employees are also crucial to the process and its success, so prior to dry-off is an optimal time for a veterinarian to visit and retrain the farm staff.
Post-Dry-Off Monitoring
Another point that Bakker makes is the importance of checking cows’ udders daily to feel if they are swollen or feverish and hot to the touch after dry-off.
“For several weeks post-dry-off, it’s important that farmers touch the udder, so they can feel if the udder is hot or swollen,” Bakker noted. “Also, check to see if dry-off cows are active—getting up to go to the feed bunk and to get water. You want to make sure they are active and functioning as you’d expect. If they are not, it may be a sign of infection. The first week after dry-off is most important.”
Proven Efficacy of SDCT
A 2021 systematic review and meta-analysis investigating the efficacy of SDCT compared to blanket dry cow therapy showed that SDCT “reduced the use of antimicrobials at dry-off without any negative effect on udder health or milk production during the first months of the subsequent lactation, if, and only if, internal teat sealants are used for healthy, untreated quarters per cow.” Also, SDCT reduced the use of antibiotics at dry-off by 66%.1
Importance of Diagnostic Testing for Successful SDCT Programs
Diagnostic testing and monitoring are essential to implementing a SDCT program. In Europe where SDCT is or is soon becoming regulated in many countries, milk from an infected cow is tested to determine if the mastitis is caused by a gram positive or gram negative bacteria. Diagnostic testing such as real-time PCR is a quick and effective way to identify the mastitis-causing pathogen, along with whether it is gram positive or negative, in order to properly treat the infection.
Standardization of SDCT Protocols
In the Netherlands, the protocol for SDCT is the same on every farm:
- Producers start with individual somatic cell count (SCC) from data collected by DHI (Dairy Herd Improvement) sampling for cows that are ready to dry off.
- For cows, antibiotics can be used if an individual SCC is above 50,000. For heifers, the threshold for a SCC is 150,000. Cows under those thresholds are not eligible to receive any antibiotic therapy; a teat sealant can be applied at dry off.
- If eligible for antibiotics, producers determine the antibiotic that is prudent to use:
- First choice—can be used “empirically,” e.g., before it is known which bacteria are causing the infection and without carrying out sensitivity testing
- Second choice—can only be used if sensitivity testing (e.g., diagnostic testing with real-time PCR to see whether the bacteria are resistant to certain antibiotics) shows that first-choice antibiotics would be unlikely to work
- Third choice—can only be used if sensitivity testing shows that neither first- nor second-choice antibiotics would work
Real-Time PCR Diagnostics for Herd Health
“As a veterinarian, if I must make the choice between first- and second-choice dry-off therapy, it’s always problem driven. If the cure rate is very low, then we must dive into it and determine what’s going on with that cow or the herd,” he said. “I always start with real-time PCR, just to make sure I know if it’s a gram-negative or gram-positive problem, and after that, I go to the antibiotic susceptibility test.”
Real-Time PCR to Monitor SCC Levels & Diagnose Mastitis
Speed is Key
Speed is a key benefit with PCR because results are often available the same day. This is especially true for Bakker because he’s performing the PCR tests in his own lab. He also likes to deliver the results directly to his client. Diagnostic testing is also needed to monitor clinical mastitis and SCCs during lactation, but it’s especially important in early lactation.
Related: Diagnosing Bovine Mastitis: Real-Time PCR for Fast Results
See these related articles about Real-Time PCR and Bovine Herd Health:
• Protect Herd Health and Productivity With Real-Time PCR
• The Importance of Sensitivity and Specificity in Diagnosing Bovine Mastitis
• Diagnostic Solutions for Dairy Cattle
（February 18, 2022. From “ The Cattle Site”）
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Post time: Feb-18-2022