Rafael Portillo-Gonzalez, Samantha Locke, and Greg Habing, Department of Veterinary Preventive Medicine, The Ohio State University
Why is it Important to Monitor Antimicrobial Use on Your Farm?
Antimicrobial resistance occurs when bacteria evolve to survive antimicrobial treatments, making infections harder to treat. Although this process happens naturally, it is accelerated by the misuse and overuse of antimicrobials. On dairy farms, bacterial infections such as mastitis, metritis, diarrhea, respiratory diseases, and lameness significantly affect animal health. Improper management of these infections can lead to the development of resistant bacteria, which will make treatment of previously minor infections in cattle difficult or impossible. Additionally, some resistant bacteria can spread to humans, causing serious health issues. Responsible use of antimicrobials minimizes the risk of resistant infections, protects animal welfare, and improves treatment outcomes. Monitoring antibiotic use at the farm level is key to maintaining responsible use and complying with regulations. It also optimizes farm efficiency by reducing the risk of antimicrobial residues in food products. By tracking antibiotic use, farmers can make data-driven decisions to improve animal health, reduce the need for antimicrobials over time and contribute to the global fight against antibiotic resistance.
How Do We Measure and Monitor On-farm Antimicrobial Use?
Antimicrobial use (AMU) is measured by determining how frequently animals on a farm receive antimicrobial treatments over a specific period (Figure 1). One common method to assess antibiotic use is by calculating the Animal Daily Dose (ADD). This metric standardizes the definition of a “dose” for each antibiotic and shows the number of doses of antibiotic used for a standard population size over time. For instance, 10 ADD per 1000 cow-days means that a farm uses, on average, 10 doses of antibiotics every day for every 1000 cows on the farm. This standardized metric helps identify patterns in antibiotic use within farms or allows apples-to-apples comparisons across farms, leading to better decision-making regarding responsible and effective use.
Figure 1. Record keeping is very important in management of antimicrobial use.
Monitoring antibiotic use alongside disease metrics, such as metritis or mastitis incidences, provides a comprehensive view of antibiotic use and treatment practices at the farm level. Disease incidence indicates how frequently health issues occur, while antibiotic use metrics reveal how antimicrobials are used in response. Together, these measures help identify patterns such as overuse or under-treatment, enabling more informed management decisions.
How Much Variation in Antibiotic Use is There Between Farms?
The variation in antibiotic use between farms can be substantial, influenced by how each farm manages animal health, identifies disease, and designs treatment protocols. A recent study published by our research team aimed to describe and quantify on-farm antibiotic use in large dairy farms in Ohio and California. The study found substantial differences in AMU among enrolled dairy farms. The overall mean treatment ADD was 11.8, with values ranging from 1.7 to 71.6 ADD/1,000 cow-days (Portillo-Gonzalez et al., 2023; Figure 2). This considerable variation highlights opportunities to reduce antimicrobial use on some farms, promoting more responsible practices. (Link to the study: https://pubmed.ncbi.nlm.nih.gov/38056568/)
Figure 2. Mean Animal Daily Dose (ADD)/1,000 cow-days by farm for the whole study period (180 days). The overall mean ADD for all the farms (n=18) was included as a reference.
Why does the Amount of Antibiotic Use Vary so Much Between Farms?
Variation in the amount of on-farm antibiotic use can be influenced by disease incidence, disease case definitions, and the design of on-farm treatment protocols. Farms with weaker disease prevention practices, such as inadequate vaccination, biosecurity, or barn hygiene, naturally tend to rely more heavily on antimicrobials. Also, the disease case definition plays an important role. Some farms may be very selective with antimicrobials by using alternatives (fluids, anti-inflammatories) or by identifying only the cases most likely to benefit from treatment. Lastly, the dose and duration specified in the veterinary treatment protocol significantly impact total antimicrobial use on the farm. For example, some farms in our study treated mastitis for a longer duration than was necessary. Changing the protocol to a shorter, yet equally effective, duration resulted in a marked reduction in antibiotic use.
How Can Farms Monitor Their Own AMU?
Farms can monitor their AMU by keeping appropriate records of each antimicrobial treatment,
including antimicrobial name, dosage, route of administration, withholding period, the number of animals treated, and the reason for use. Herd management software can help organize treatment records, which can then be used more easily for analysis. Farms can work with their veterinarian to calculate ADD, monitor sales records, and monitor inventory. Analyzing these records alongside other performance indicators can help identify areas where enhanced disease prevention measures or adjustments to treatment protocols may be needed.
What Can Producers Do to Reduce Their AMU?
Dairy farmers can reduce AMU by focusing on four key strategies. The first and most obvious strategy is to reduce disease incidence and therefore reduce the need for antimicrobials. This can be achieved through appropriate nutrition, vaccination, improved biosecurity, and early disease detection, which helps prevent outbreaks and reduces the need for antimicrobial treatments. Second, farms should work closely with their veterinarian to regularly review the adherence to treatment protocols. The protocol should include clear directions on the disease case definition so that antimicrobials are only administered to cows likely to benefit from the treatment. Accurate disease identification requires substantial training and experience, and some infections may resolve or worsen without antimicrobials. Treatment alternatives, such as fluids and anti-inflammatories, can further lower antimicrobial dependence. Third, producers should also review treatment protocols with their veterinarian to ensure that the dose and duration of treatments are appropriate. Adjusting these factors can prevent overuse while maintaining treatment efficacy. Lastly, producers might consider selective dry cow therapy, which targets antimicrobials only for cows at higher risk of infection or those with existing infections, such as high somatic cell counts (SCC). On some farms, this method has successfully reduced AMU while maintaining udder health.
Reductions in unnecessary antibiotic use can improve animal health, enhance farm sustainability, and play a vital role in combating antibiotic resistance, which is critical for public health and the future efficacy of antimicrobials.