Quick facts
- A selective dry cow therapy (SDCT) program treats some cows at dry off with an antibiotic.
- SDCT can reduce antibiotic use and costs for dairy farms.
- All cows should be treated with an internal teat sealant.
- SDCT is not appropriate for every dairy farm.
- Well trained employees and veterinary involvement are crucial for SDCT success.
Dry cow therapy
Intramammary infusion with long-acting antibiotics at dry off (dry cow therapy) is a long-standing practice in the dairy industry and for good reason.
- Dry cow therapy (DCT) is associated with:
- Curing existing infections at dry off.
- Decreased risk of new infections during the dry period.
- Reduced risk of clinical mastitis in early lactation.
- Decreased somatic cell count (SCC) in early lactation.
- The practice of blanket dry cow therapy (BDCT), treating every cow at dry off, has significantly contributed to reduced prevalence of Staphylococcus aureus and Streptococcus agalactiae.
What is selective dry cow therapy (SDCT)?
Selective dry cow therapy (SDCT), as opposed to blanket dry cow therapy (BDCT), employs a specific strategy to avoid treating every cow with antibiotics at dry off.
- BDCT accounts for approximately one-third of the total antibiotic use on a conventional dairy.
- SDCT can provide a more targeted approach and a more judicious use of antibiotics without compromising future cow health or performance.
- SDCT programs identify two categories of cows:
- Cows eligible for treatment with antibiotics and internal teat sealant.
- Cows eligible for treatment with internal teat sealant alone.
Why should producers consider SDCT?
Increasing public concern about antibiotic use in agriculture has led the dairy industry to explore ways to use antibiotics in a more judicious manner.
- BDCT accounts for approximately one-third of the total antibiotic use on a conventional dairy farm, and SDCT has been shown to reduce dry cow antibiotic use by 55%.
- Decreased use of antibiotics also means that producers have the opportunity to save money with a SDCT program.
- A cost-saving calculator is available through the UMN College of Veterinary Medicine dairyKnow website.
What dairy farms have the best chance of SDCT success?
SDCT is not the correct choice for every producer. Specific herd criteria help identify when an SDCT program is most appropriate to implement and include:
- An annual bulk tank somatic cell count (SCC) less than 250,000 cells/ml.
- Contagious mastitis pathogens are under control (low numbers of Staphylococcus aureus and Streptococcus agalactiae).
- Use of teat sealant in all quarters of all cows at dry off.
- Correct technique for intramammary infusions at dry off.
- Well-trained personnel to make correct screening and treatment decisions.
- The ability to monitor the program to verify it is working.
How to identify which cows to treat with antibiotics in an SDCT program
There are two approaches to classify cows in an SDCT program: an algorithm-guided method and a culture-guided method.
Herds that routinely test with DHIA or have access to similar data can use an algorithm-guided method to categorize cows. Those herds without access to reliable SCC and clinical mastitis records may need to use a culture-guided method.
- Algorithm-guided and culture-guided SDCT programs both show a similar reduction in dry cow therapy antibiotic use.
- There is no difference in effectiveness between the two methods in terms of significant cow health or production outcomes according to a multi-herd, multi-state study led by University of Minnesota researchers.
- While both approaches had a positive average net return, there is potentially greater cost-savings associated with an algorithm-guided SDCT program if adequate DHIA records are already available.
Criteria to identify groups of cows in an algorithm guided SDCT program
Cows eligible for treatment with antibiotics and internal teat sealant in all four quarters can meet ANY of these criteria:
- SCC greater than 200,000 at any test during the current lactation.
- Any clinical mastitis cases in the last 14 days of lactation.
- 2 or more clinical mastitis cases during the current lactation.
Cows eligible for treatment with internal teat sealant alone in all four quarters must meet ALL of these criteria:
- Lactation SCC less than 200,000 for all tests during the current lactation.
- No clinical mastitis in the last 14 days of lactation.
- Less than 2 clinical mastitis cases during the current lactation.
In culture-guided SDCT, aseptic milk samples are collected 2 days before dry-off and cultured to identify subclinical mastitis that would require treatment with dry cow antibiotics. Inexpensive rapid culture may be conducted on the farm for farms with a milk culture lab already in place or may be conducted in the local veterinary clinic.
In addition to culture results, producers may use additional information gathered from SCC and clinical mastitis records to determine cow eligibility for treatment. There are two culture-guided methods for SDCT.
Quarter sampling culture
Each quarter of the udder can be cultured and categorized separately. A positive culture makes the quarter eligible for antibiotics and internal teat sealant, while a negative culture is eligible for internal teat sealant alone. The Minnesota Easy® 4Cast® plate is designed for quarter culture use and is available through the UMN Laboratory for Udder Health.
Composite sampling culture
Sampling all quarters of the udder and combining those into one sample is also an option for culture-guided SDCT. This method reduces dry cow therapy antibiotic use, but less so than for the quarter sampling culture approach or the algorithm guided methods.
How to monitor a SDCT program
As with any big decision on a dairy, it is crucial to work with the herd veterinarian to monitor and evaluate the program. An ideal monitoring program includes continual evaluation of milk quality and the SDCT program.
- Regular bulk tank cultures to screen for contagious pathogens.
- SCC testing.
- Routine culture of clinical and chronic mastitis cases.
- Monitoring cows for mastitis during the dry period, particularly just after dry off.
- Monitoring clinical mastitis rate and SCC in early lactation
- Veterinary involvement and evaluation of records.
For herds using the culture approach, monitor the cleanliness of samples, since a high contamination rate will result in unnecessary use of antibiotics, reducing the net-return of the program.
SDCT keys to success
Successful SDCT programs are highly dependent on a few key factors.
- Use of an internal teat sealant in quarters not treated with dry cow antibiotics
- A proper intramammary infusion technique is essential. Failure to follow aseptic technique can result in the introduction of harmful pathogens to the udder.
- Well trained, vested employees are crucial.
Veterinary involvement is strongly encouraged to help set protocols, train employees, and monitor the program. In some cases the herd veterinarian could also provide trained, experienced veterinary technicians to do sampling or to conduct dry-off procedures.
SDCT is not something all herds should implement. Producers should work with their veterinarian to make sure an SDCT program is right for their herd using the appropriate herd criteria.
This infographic is available in alternative formats on request.
Rowe, S. M., et al. "Randomized controlled non-inferiority trial investigating the effect of 2 selective dry-cow therapy protocols on antibiotic use at dry-off and dry period intramammary infection dynamics." Journal of Dairy Science (2020).
Rowe, S. M., et al. "Randomized controlled trial investigating the effect of 2 selective dry-cow therapy protocols on udder health and performance in the subsequent lactation." Journal of Dairy Science (2020).
Reviewed in 2023