By Dr. Michael Payne, UC Davis, School of Vet. Medicine; Director, CDQAP
Producer’s wanting to reduce antibiotic use should consider Selective Dry Cow Therapy, but it won’t be for everyone.
Since the 1940s, as human medicine’s dependence on antibiotics has accelerated, so has bacterial pathogens’ ability to resist those treatments. The Centers for Disease Control estimates that every year about 2.8 million Americans develop antibiotic resistant infections, with some 35,000 of them dying from it.
This crisis in human health has spurred millions of dollars of research and mitigation programs. In California for instance, every human hospital and nursing home must implement a plan describing how the facility will minimize development of antibiotic resistant strains.
Focus on Antibiotics in Livestock – Efforts have also been made to slow the development of resistance in livestock and poultry. Implemented in 2013, FDA’s strategy required veterinary oversight of antibiotics used in feed and water, and also prohibited using antibiotics to increase weight gain and production. In 2018, California led national efforts to further reduce resistance by requiring all antibiotic use in food animals to be overseen by a veterinarian. In June of this year, federal regulations will mimic California’s legislation, requiring veterinary antibiotic management in all 50 states.
Focus on Dry Cow Treatments – Most antibiotics sold for use in food animals are administered in feed or water, a practice that, for milk quality reasons, isn’t used in dairy cows. Similarly, the use of dry and lactating intramammary treatments accounts for less than 1% of all antibiotics given to animals. There is no data suggesting dry cow treatment promotes development of significant resistance. The combination of dry and lactating treatments does however remain the most common antibiotic use on dairies, making it a potential target for legislation.
In 2021, Maryland prohibited the use of Blanket Dry Cow Therapy (BDCT), meaning routine treatment of all quarters in all cows at dry-off. Under the new regulation, any cow receiving dry-treatment must first be diagnosed as having an infection, using a test method approved by the state’s Secretary of Agriculture. New York has a similar draft legislation.
Blanket Dry Cow Therapy – BDCT programs became standard practice in the 1970’s when contagious pathogens like Strep agalactiae and Staph aureus were a common challenge for producers. Blanket therapy’s effectiveness explains its persistence in most dairy’s mastitis control programs today; more than 94% of large dairies still use blanket dry cow treatment. Consequently, dry treatment accounts for about 40% of all antibiotic treatments used on dairies. Because cull cows and heifers are not typically treated, not all cows on the dairy are treated.
Selective Dry Cow Therapy – Infections by contagious mastitis pathogens are far less common than in previous decades. Selective Dry Cow Therapy (SDCT), treating only those cows or quarters with evidence of infection, has the potential to reduce antibiotic use and possibly even treatment costs. Numerous studies have compared blanket verses selective dry cow therapy. Collectively this research provides important guidance for producers considering SDCT:
- SDCT does reduce use of antimicrobials on the dairy, typically something in the range of 30% and 60%, depending on the program.
- SDCT can result in modest savings of treatment costs, with one model estimating savings of between 30 cents and $2.30 per cow.
- Use of internal teat sealants, such as Orbeseal® or Lockout®, in untreated quarters is essential for the success of a SDCT program.
- SDCT can be effective for some operations, but proper selection of herds is critical to prevent potential mastitis surges.
Selecting Cows for SDCT – Perhaps the thorniest question for producers implementing SDCT is how to determine, accurately and economically, which cows to treat. Some dairies have had great success setting up On-Farm Culture programs for quarter milk samples. Such programs do however have associated material and labor costs. In addition, there may be up to a 40% false negative rate, resulting in undertreatment of subclinical infections.
Recent studies demonstrate that a selection algorithm incorporating monthly SCC data and clinical mastitis history can be as effective as culture in determining which cows need to be treated. For the more than half of California dairy herds already using monthly testing, such an algorithm could be an economical solution. Alternatively, producers using robotic milkers may have real-time access to SCC through sensor data. Finally, there may be some commercially available on-farm SCC test kits that could be used, but the accuracy of those assays has yet to be determined.
SDCT Isn’t for Everyone – Not every herd is ready for SDCT. Typical recommendations for good candidates for a SDCT program include:
- herds that have eliminated Strep agalactiae and Staph aureus
- herds that routinely culture bulk tanks and have a Bulk Tank SCC of less than 250,000
- herds with a clinical mastitis incidence rate of less than 5% per month
- herds that forestrip and that have with good clinical mastitis records