By Dr. Michael Payne, UC Davis, School of Veterinary Medicine; Director, CDQAP

The federal Food and Drug Administration is poised to require nation-wide veterinary oversight of the use of medically important antibiotics in all livestock. The new requirement will be enacted probably by mid-2023. In part this means that regardless of the type of livestock or poultry being raised, farmers wanting to use antibiotics that are also used in human medicine will need a prescription from their herd or flock veterinarian.

While the change may be important in other states, it won’t affect producers in California. Since 2018, with the passage of Senate Bill 27, California has already required livestock producers to consult with their herd veterinarians on antibiotic use. In fact, rather than concerning news, this new national initiative by FDA not only levels the regulatory playing field across the country, it also highlights the progress the California’s livestock industries have made over the last four years.

California’s Leadership on Antibiotic Stewardship

At the heart of the state’s effort to preserve antibiotic effectiveness is CDFA’s Antimicrobial Use & Stewardship (AUS) Program. Consisting of veterinarians, epidemiologists and specialists, the program addresses the complex issue of antibiotic resistance on a variety of fronts. This includes data collection of antibiotic sales, monitoring development of drug resistance, surveys of industry practices, funding research on antibiotic alternatives and industry outreach.

In partnership with CDFA, California producers have led the nation in adaption of practices which help preserve the effectiveness of antibiotics for humans and livestock alike. Even before the implementation of the new regulations, 92% of the state’s dairy producers already relied on their herd veterinarian for antibiotic guidance. In the years after SB 27, California dairy farmers have reported increased use of alternatives to antibiotic drugs, increased sampling for disease diagnosis and changes to their practices in order to control and prevent disease outbreaks.

Testing for Resistance on the Farm

These efforts seem to be working. Of particular interest to dairy veterinarians is CDFA and USDA data on pathogen sensitivity to various antibiotics. Testing of some 4,329 isolates from dairy cow manure, for instance, indicated a low rate of antibiotic resistance to drugs commonly administered to adult dairy cows. CDFA continues to collect and summarize antibiotic susceptibility data from livestock in California, to assist producers and veterinarians in selecting the lowest cost drug which is still effective.

There are some caveats however when using antibiotic susceptibility testing for animal pathogens. The older susceptibility testing method, the Kirby-Bauer disk assay, is correlated to human antibiotic blood concentrations, and has little relevance to drug concentrations in the udder achieved by intramammary mastitis tubes. In addition, even for therapies which testing indicates the bacteria should be sensitive, there may be individual cases that fail to respond, like Staph cows that have abscesses or significant scar tissue.

In order to address these human/animal disconnects, CDFA is referencing animal-specific interpretive data generated by the Clinical and Laboratory Standards Institute, CLSI. This technology utilizes the gold standard of sensitivity testing, Minimum Inhibitory Concentration (MIC). For more information on California-focused livestock pathogen sensitivity, veterinarians can sign up to have information delivered directly to their email.

Return on Investment for the Dairy

Antibiotic stewardship isn’t just about helping protect antibiotic use in human medicine. Careful selection of which antibiotics are used on the farm can be a powerful tool in preserving efficacy of treatments and reducing treatment costs on the dairy as well. As described in this video from CDQAP, using periodic sampling from mortalities, the herd veterinarian can determine which strains of bacteria are causing disease and which antibiotics they are sensitive to. Picking the “right drug for the right bug” not only assures treatment will be effective but also allows vets to select the least costly treatment. There’s no point, for instance, in treating weanling pneumonia in a calf with a later-generation cephalosporin, costing several dollars a day, if the bacterial strain is also sensitive to a tetracycline costing only pennies each day.

New Mastitis Research

Interest in reducing both the cost of mastitis and antibiotic use has led to renewed focus on Selective Dry Cow Therapy (SDCT), a management practice where only infected or at-risk cows are treated. Recent research using data from California dairies estimated that following implementation of SDCT, a 29% reduction of antibiotics used in dry cows could be achieved with no adverse economic impact to the producer. Producers are cautioned however that not every dairy is a good candidate for SDCT. Producers should perform a complete review of their mastitis management with their herd veterinarian before the implementation of an SDCT program.

How much does a case of clinical mastitis cost a California producer? New research from UCD estimates a single case of clinical mastitis on average costs about $295, with the greatest losses due to decreased production and discarded milk. A customizable mastitis cost calculator is available.

Resources on Antimicrobial Stewardship

For producers interested in learning more about antibiotic stewardship there’s a wealth of information available on-line. For California producers here are some good places to start:

Antibiotic Resistance and Dairy Producers Videos: Produced by CDQAP and UCD, this series of four short videos explain clearly and graphically what antibiotic resistance is, why producers have a stake in it and how to combat it.

Frequently Asked Questions: Produced by CDFA’s Antimicrobial Use and Stewardship (AUS) program, this 2-page fact sheet explains the basics of California’s plan to address antibiotic resistance in livestock.

Antimicrobial Stewardship Planning Workbook: Produced by CDFA’s (AUS) program, this 9-page workbook is one way to open discussion between you and your veterinarian to review your drug use program and get started reducing drug use and therapy costs.