Antimicrobial use in Swiss dairy farms: Quantification and evaluation of data quality

Antimicrobial Resistance and Use on Chinese Dairy Farms: Awareness and Opinions Regarding Selective Treatments of Farm Managers

BACKGROUND

In China's expanding dairy industry, a lack of oversight regarding antimicrobial use and increasing antimicrobial resistance are evident. Selective treatments of dairy cows for clinical mastitis or dry cow therapy are proposed to promote judicious antimicrobial use without adversely impacting cattle health. These approaches have been successfully implemented on farms in other countries.

METHODS

On 28 October 2023, a 2-day in-person seminar was held in Beijing, China, on selective antimicrobial treatments of dairy cows for clinical mastitis or dry cow therapy on large Chinese dairy farms. Concurrently, a qualitative study involving 15 technical managers from the 13 largest Chinese dairy groups used focus group discussions and questionnaires to explore perspectives on selective treatments of dairy cows for clinical mastitis or dry cow therapy. The main outcomes assessed were opinions and concerns regarding implementing selective antimicrobial treatments.

RESULTS

Although there was diversity of cognition on AMR and selective treatments, the technical managers were generally positive regarding adoption of selective treatments. However, they expressed a need for more evidence and tools, including anticipated economic impacts, effects of delaying treatment until diagnosis, accurate interpretation of milk recording data, safe use of internal teat sealants, and spread of pathogens. Participants stressed the need for awareness, staff training, farm management, and China-specific standards, suggesting large-scale trials to assess efficacy of selective treatments.

CONCLUSION

The findings revealed key challenges and barriers currently impeding selective AMU practices. These insights could inform efforts to promote judicious AMU on farms through targeted treatment regimens, reducing mounting selective pressure driving resistance.

Associations of the Swiss national reporting system's antimicrobial use data and management practices in dairy cows on tiestall farms

Antimicrobial use (AMU) in Switzerland is above target and requires reduction, especially in dairy cattle. Measuring AMU is pivotal to identifying starting points for AMU reduction, and so are studies investigating its potential drivers in dairy farms worldwide. However, although AMU in dairy farms is high, studies estimating AMU specifically in tiestall farms are scarce. Tiestalls are a common housing system and their prevalence among dairy farms accounts to approximatively 73%, 41%, and 40% in Canada, the United States, and Switzerland, respectively. The objectives of this cross-sectional, retrospective observational study were to estimate AMU using the newly established Swiss national reporting system for AMU in livestock and to identify associated factors on Swiss tiestall dairy farms. We calculated the treatment incidence (TI) by using the European Medicines Agency methodology and their defined daily dose (DDD) and defined course dose (DCD) standards. Data on factors potentially associated with AMU were obtained through personal interviews with farm managers on 221 farms. Retrospectively, during a 1-year period, data on a total of 7,619 treatments were extracted from the national database. Associations between management factors and TI were analyzed using a generalized linear model with gamma distribution. The mean (± SD) overall TI was 5.46 DDD/cow-year (± 4.10 DDD/cow-year). Intramammary treatment during lactation accounted for highest TI (3.24 ± 3.16 DDD/cow-year), whereas dry-cow therapy accounted for lowest TI (0.44 ± 0.49 DCD/cow-year). We found that 5 of the investigated management factors were significantly associated with TI. Organic production (estimate = -2.16; 95% CI = -3.62 to -0.70) and herd size (estimate = -0.81; 95% CI = -1.23 to -0.39) were negatively associated with TI. Specific cow breeds (Brown Swiss estimate = 1.56; 95% CI = 0.45-2.68) and Holstein Friesian (estimate = 1.42; 95% CI = 0.03-2.82; reference: other breeds) and the use of hygienic powders on the lying area (estimate = 1.10; 95% CI = 0.04-2.17) were positively associated with TI. Overall, the Swiss national reporting system is a valuable tool for AMU estimation. Several herd characteristics and management factors were associated with AMU in tiestall farms. Further studies focusing on factors associated with AMU and which are amenable to intervention will help improve stewardship programs and subsequently reduce AMU in dairy cows.

Quantification of antimicrobial use on Irish dairy farms: A comparison of three recording methods

Antimicrobial use (AMU) data are essential for monitoring usage over time, facilitating reduction strategies to combat the threat of antimicrobial resistance (AMR) to both human and animal health. The objective of this study was to measure and describe AMU over a 12-mo period in Irish dairy herds and compare 3 different recording methods to a reference method. A sample of 33 Irish dairy herds were randomly selected from 6 private veterinary practices across Ireland. The herds were followed for a 12-mo period and their AMU was monitored using 3 recording methods: 1. Veterinary prescription data (VET), 2. The inventory of medicine bins on the farms (BIN), and 3. Farmer treatment records from herd recording software (APP). Each recording method was compared with a previously developed reference method for AMU. The reference method used was based on pre- and poststudy medicine stock on the farms combined with veterinary prescription data. Antimicrobial use was analyzed using both mass- and dosed-based metrics, including mass (mg) of antimicrobial active ingredient per population correction unit (mg/PCU), defined daily doses for animals (DDDVET) and defined course doses for animals (DCDVET). Median AMU was 16.24, 10.47, 8.87 and 15.55 mg/PCU by mass, and 2.43, 1.55, 1.19 and 2.26 DDDVET by dose for VET, BIN, APP, and reference method data, respectively. Reliability of the agreement between each pair of methods was quantified using the concordance correlation coefficient (CCC). When compared with the reference method, VET data had excellent reliability [95% confidence interval (CI) of CCC: 0.992-0.998]. The BIN data had good to excellent reliability [95% CI of CCC: 0.776-0.936]. The APP data had poor reliability when compared with the reference method [95% CI of CCC: -0.167-0.156]. Our results highlight that a small number of herds were contributing most to overall use and farmers showed varying levels of consistency in recording AMU. Veterinary data were the most reliable approach for assessing AMU when compared with a reference method of AMU. This is an important finding for the future monitoring of AMU at a national level.

Surveillance of Antimicrobial Resistance of Escherichia coli Isolates from Intestinal Contents of Dairy and Veal Calves in the Veneto Region, Northeaster Italy

This surveillance study aimed to estimate the proportion of antimicrobial resistant strains and antimicrobial resistance (AMR) profiles of E. coli isolates detected from the intestinal contents of veal and dairy calves in the Veneto Region, Northeaster Italy. Additionally, we investigated the differences in AMR profiles between dairy and veal calves over the period 2017-2022. Overall 1150 E. coli isolates were tested from calves exhibiting enteric disease, with 868 from dairy and 282 from veal calves. The percentage of resistant isolates to nine antimicrobials was notably higher in veal calves compared to dairy calves, except for ampicillin. Throughout the study period, we observed a significant increase in the proportion of resistant isolates to florfenicol, gentamycin, paromomycin, tetracycline and trimethoprim/sulfamethoxazole in dairy calves, while we did not detect any significant increase in the proportion of resistant isolates among veal calves. A substantial proportion (75.9%) of the isolated E. coli exhibited multi-drug resistance (MDR). The proportion of multi-drug resistant isolates was significantly higher in veal calves (91.7%) compared to dairy calves (74.3%) all through the surveillance period (2017-2022), with no significant variation in MDR proportion among veal calves between 2017 and 2022 but a significant increase among dairy calves.

Antibiotic use in the Northern Irish sheep flock: What lessons can be learnt from medicine records and farmer attitudes to improve stewardship of these essential medicines?

Stewardship of antibiotics used in livestock production has come under increasing scrutiny, from both the animal welfare point of view and due to concerns that antibiotic use in livestock may pose a risk to human health through selection pressure to drive development of antibiotic resistant strains of bacteria. Despite this concern, however, antibiotic consumption in the sheep sector is currently poorly described. This study determines the range and quantities of antibiotics used in the Northern Irish (NI) sheep flock as well as exploring drivers for their use. A mixed-methods approach was utilised, with an anonymous online scoping survey, analysis of the medicine records from 52 NI sheep farms and semi-structured interviews undertaken with 27 farmers. Eighteen farmers contributed both records and participated in interviews. Veterinary medicine records were derived from two sources: on-farm medicine books (seven) or veterinary practice sales data (51). As six of these farmers provided information from both sources a total of 52 unique farms participated. Overall, antibiotic use in sheep on the 52 farms sampled was low, with a median value of 11.35 mgPCU-1 (mean 13.63 mgPCU-1, sd 10.7; range 0-45.29 mgPCU-1), with all farms below 50 mgkg-1. Critically important antibiotics accounted for 0.21% of all antibiotics purchased. Lameness was the main driver of antibiotic use identified by this study. Others included a range of prophylactic treatments such as oral antibiotics to prevent watery mouth, injectable antibiotics to prevent abortion and following assisted lambing. Farmers acknowledged some of these uses had become habitual over time. The veterinary medicine sales records demonstrated significant sales of antibiotics not authorised for use in sheep, on an ongoing, rather than case-by-case, basis. Farmers were positive about their veterinarian's ability and knowledge to improve flock welfare and productivity, but were unwilling to pay for this advice. However, veterinarians may have facilitated weak medicine stewardship through a failure to adequately challenge farmers seeking antibiotics. Farmers did not maintain accurate or up-to-date on farm medicine or production records in the majority of cases. Despite this lack of on-farm recording, veterinary sales records can be studied in consultation with farmers to provide veterinarians with a farm-specific insight into antibiotic use and related attitudes and behaviours. Farmers and veterinarians can then identify areas and behaviours to target collaboratively, improving antibiotic and wider medicine stewardship, whilst simultaneously improving flock health and productivity.

Effect of a dairy farmworker stewardship training program on antimicrobial drug usage in dairy cows

Antimicrobial use (AMU) is critical to preserving animal health and welfare. However, the development of antimicrobial resistance (AMR) represents a public health threat. Although most antimicrobials used on the farm require a veterinarian prescription, farmworkers make daily on-farm treatment decisions. Therefore, farmworker training is vital to promote responsible AMU. This research project aimed to evaluate the effect of farmworker antimicrobial stewardship (AMS) training on the quantity of AMU on dairy farms in Ohio and California. We hypothesized that farms receiving AMS training would have reduced AMU in dairy cattle compared with farms where training wasn't administered. We designed a quasiexperimental study with 18 conventional dairy farms enrolled in Ohio and California. Twelve farms received AMS training, and 6 farms did not. The AMS program included a 12-wk training focused on accurate identification of cows requiring antimicrobial treatment. We quantified AMU by collecting used drug containers, manually counted by researchers during farm visits. Treatment incidence (TI) was calculated using animal daily doses (ADD), and Poisson regression models were used to analyze the TI data. Disease incidence rate (DIR) in lactating cows was 2.2, 1.5, 1.0, 0.4, 0.3, 0.2, and 0.03/1,000 cow-days for mastitis, lameness, metritis, pneumonia, retained placenta, diarrheas, and other diseases (e.g., conjunctivitis, injuries), respectively. The highest TI by antimicrobial class (provided in ADD/1,000 cow-days) was cephalosporin (5.9), penicillin (5.2), tetracyclines (0.4), lincosamides (0.2), and sulfonamides (0.1). Among the trained farms using a within-treatment group analysis, no significant differences were observed in TI pre-intervention (10.9 ADD/1,000 cow-days) compared with TI postintervention (10.3 ADD/1,000 cow-days). Treatment incidence from the training group was 10.8 ADD/1,000 cow-days and although numerically lower, it was not significantly different compared with TI in the control groups at 13.9 ADD/1,000 cow-days (rate ratio = 0.77, CI = 0.25-2.38). Future research on AMS should incorporate farmworker training with social science approaches to overcome barriers and promote on-farm responsible use.

Barriers to recording calf health data on dairy farms in Ontario

Establishing accurate illness and treatment rates in dairy calves is crucial, yet calf health records are often incomplete. Thus, the objective of this study was to investigate barriers for dairy farmers for recording calf illnesses and treatments on dairy farms in Ontario, Canada. An online survey was completed by a convenience sample of 88 Ontario dairy farms in 2022, with 34 questions regarding farm demographics, current practices surrounding record keeping and analysis, and factors that would improve recording compliance. Multivariable models were built to assess associations between explanatory variables and the following outcomes: likelihood of making management or treatment protocol changes based on records analysis, factors that would increase the use of electronic recording methods, and whether all calf illnesses and treatments are recorded. Pearson's chi-squared tests were also used to investigate associations between explanatory variables and whether the respondent agreed or disagreed with a proposed reason for why a calf illness or treatment would not be recorded on their farm. Producers had 3.45 times greater odds of recording all antimicrobial treatments if they used a computer software system compared with those that did not. With respect to anti-inflammatory treatments, producers had 3.11 times greater odds of recording these treatments if records were located in the calf barn than elsewhere. Nonfamily employees had 6.08 times greater odds of recording all supportive therapy treatments than farm owners. When calf health records were kept in the calf barn, respondents were less likely to report that illnesses were not recorded due to time constraints (5% vs. 36% if records were elsewhere) or because calf health records were not analyzed (10% vs. 34% if records were elsewhere). On farms that recorded calf treatments in a paper booklet, respondents were more likely to report that treatments were not recorded because calf health records were not analyzed (44% for paper records vs. 21% for other systems). The most commonly indicated factors that would increase recording of illness were recording with a mobile app (27% of respondents) and for the recording system to be easy to use (31% of respondents). Overall, these data indicate that recording may be improved by keeping calf health records in close proximity to the calves and using a recording method that allows for data analysis. An easy-to-use mobile app may also improve recording if it could be used in the calf barn, provide data analytics, and allow for time-efficient data entry.

Adoption and decision factors regarding selective treatment of clinical mastitis on Canadian dairy farms

As clinical mastitis (CM) treatments are responsible for a large portion of antimicrobial use on dairy farms, many selective CM treatment protocols have been developed and evaluated against a blanket treatment approach of CM cases. Selective treatment protocols use outcomes of diagnostic tests to exclude CM cases from antimicrobial treatment when they are unlikely to benefit. To tailor interventions to increase uptake of selective treatment strategies, a comprehension of current on-farm treatment practices and factors affecting treatment decisions is vital. Two questionnaires were conducted among 142 farms across 5 provinces participating in the Canadian Dairy Network for Antimicrobial Stewardship and Resistance in this cross-sectional study. Self-reported adoption of selective CM treatments by dairy farmers was 64%, with median of 82% of cows treated in those herds using selective treatment. Using logistic regression models, the odds to implement a selective CM treatment protocol increased with a decreasing average cow somatic cell count. No other associations were identified between use of a selective CM treatment protocol and farm characteristics (herd size, CM incidence, province, milking system, and housing system). Three subsets of farmers making cow-level CM treatment decisions were identified using a cluster analysis approach: those who based decisions almost exclusively on severity of clinical signs, those who used various udder health indicators, and farmers who also incorporated more general cow information such as production, age, and genetics. When somatic cell count was considered, the median threshold used for treating was >300,000 cells/mL at the last Dairy Herd Improvement test. Various thresholds were present among those considering CM case history. Veterinary laboratories were most frequently used for bacteriological testing. Test results were used to start, change, and stop treatments. Regardless of protocol, reasons for antimicrobial treatment withheld included cow being on a cull list, having a chronic intramammary infection, or being at end of lactation (i.e., close to dry off). If clinical signs persisted after treatment, farmers indicated that they would ask veterinarians for advice, stop treatment, or continue with the same or different antibiotics. Results of this study can be used to design interventions targeting judicious mastitis-related antimicrobial use, and aid discussions between veterinarians and dairy producers regarding CM-related antimicrobial use.

Assessing antibiotic usage data capture accuracy on dairy farms in England and Wales

BACKGROUND

Accurate farm-level data on antibiotic usage (ABU) are needed for the surveillance of antibiotic resistance. Therefore, this study aimed to determine the accuracy of ABU data capture by dairy farmers in South West England and Wales.

METHODS

Through a cross-sectional survey of 48 dairy farmers, the accuracy of ABU recording was measured by farmers' assessment of the completeness and timeliness of ABU recording ('perceived accuracy') and the completeness and correctness of on-farm ABU records ('actual accuracy'). Completeness and correctness were compared for paper and software recording methods.

RESULTS

Perceived accuracy was higher than actual accuracy. Antibiotic names, withdrawal periods and dates that products were fit for human consumption were often incomplete or incorrect. More inaccuracies were seen with paper than software. In some software platforms, the date that milk would be fit for human consumption was frequently rounded down by half a day, increasing the risk of residue failures.

LIMITATION

The small number of on-farm records assessed limits the generalisability of the results.

CONCLUSIONS

Electronic recording of ABU should be encouraged. However, functionality needs improvement, alongside consultation with dairy farmers to increase awareness of inaccuracies.

Quantifying antimicrobial use on Canadian dairy farms using garbage can audits

Antimicrobial resistance in pathogenic bacteria is one of the preeminent concerns for the future of global health. There is a dose-dependent relationship between antimicrobial use (AMU) and the prevalence of antimicrobial-resistant pathogens. As most AMU in Canada is related to animal agriculture, there is a need to reduce overall AMU, which could be accomplished through surveillance of AMU in animal agriculture, including the dairy industry. The objective of this study was to quantify AMU on dairy farms across Canada. This study had two parts: a description of data collected in 2019-2020, and a meta-analysis comparing this data to previous estimates of AMU in the Canadian dairy industry. The first included a garbage can audit (GCA) on 107 farms in four Canadian provinces (British Columbia, Alberta, Ontario, and Nova Scotia) in 2020; AMU data were converted to the dose-based metrics of defined course doses (DCD) and defined daily doses (DDD). Mixed-effect linear models were fit to determine the relationship between province and use of different classes of antimicrobials. On average, for every 100 animals on the farm, 117 DCD of antimicrobials were administered per year (IQR: 55, 158). These treatments amounted to 623 DDD / 100 animal-yr (IQR: 302, 677 DDD/100 animal-years). Penicillins were the most used class of antimicrobials, followed by first-and third-generation cephalosporins. Farms in Ontario used more third-generation cephalosporins than other provinces. The second part of this study compared AMU in 2020 to previously reported Canadian studies through a meta-analysis. A GCA was conducted in 2007-2008 in Alberta, Ontario, Québec, and the Maritime provinces (Prince Edward Island, New Brunswick and Nova Scotia); another GCA was conducted in Québec in 2018. Overall, AMU was lower in 2018-2020 than in 2007-2008, with the exception of third-generation cephalosporin use, which increased.

Bayesian latent class models to determine diagnostic sensitivities and specificities of two point of care rapid tests (Selma plus, Dipslide) for the detection of Streptococcus uberis associated with mastitis in dairy cows

Introduction

Development and validations of accurate mastitis diagnostics are crucial to make timely and evidence-based decisions on mastitis therapy in order to reduce its impact on productivity, animal welfare and practicing the prudent use of antimicrobials on dairy farms.

Methods

The objectives of this study were to assess the agreement between test results from reference laboratory and two point of care tests (Selma plus, Dipslide) and to estimate the test accuracies with Bayesian latent class models (BLCMs). In total of 509 single quarter milk samples from cows with mastitis were included in the study.

Results

Among all analyzed mastitis pathogens, Streptococcus spp. was detected in up to one third of all analyzed samples and for Selma all Streptococcus samples were considered as Streptococcus uberis. The agreement (κ) when comparing two tests varied greatly depending on the bacteria, ranging from no agreement to good agreement (κ = negative to 0.86) depending on the prevalence of identified pathogens. Based on BLCMs to assess diagnostic test accuracies for the pathogen Streptococcus uberis, posterior sensitivities of 76, 71, and 64% for Selma plus, Dipslide and laboratory standard culture and specificities of 93%, 98% for Selma and Dipslide, respectively, were obtained.

Discussion

The two point of care rapid culture systems Dipslide and Selma plus plate can provide important preliminary pathogen identification for targeted mastitis therapy, especially when general information about growth and a rough classification of the bacteria into groups have an impact on treatment strategy. The two evaluated rapid culture systems, Dipslide and Selma plus plate, show good test accuracies for Streptococcus uberis at least at genus level. Therefore, using these tests may contribute to prudent use of antibiotics.

Antimicrobial Use and Resistance in Surplus Dairy Calf Production Systems

Surplus calves, which consist predominately of male calves born on dairy farms, are an underrecognized source of antimicrobial-resistant (AMR) pathogens. Current production systems for surplus calves have important risk factors for the dissemination of pathogens, including the high degree of commingling during auction and transportation and sometimes inadequate care early in life. These circumstances contribute to an increased risk of respiratory and other infectious diseases, resulting in higher antimicrobial use (AMU) and the development of AMR. Several studies have shown that surplus calves harbor AMR genes and pathogens that are resistant to critically important antimicrobials. This is a potential concern as the resistant pathogens and genes can be shared between animal, human and environmental microbiomes. Although knowledge of AMU and AMR has grown substantially in dairy and beef cattle systems, comparable studies in surplus calves have been mostly neglected in North America. Therefore, the overall goal of this narrative review is to summarize the existing literature regarding AMU and AMR in surplus dairy calf production, highlight the management practices contributing to the increased AMU and the resulting AMR, and discuss potential strategies and barriers for improved antimicrobial stewardship in surplus calf production systems.

Realities, Challenges and Benefits of Antimicrobial Stewardship in Dairy Practice in the United States

The use of antimicrobials for the treatment of food-producing animals is increasingly scrutinized and regulated based on concerns about maintaining the efficacy of antimicrobials used to treat important human diseases. Consumers are skeptical about the use of antibiotics in dairy cows, while dairy producers and veterinarians demonstrate ambivalence about maintaining animal welfare with reduced antimicrobial usage. Antimicrobial stewardship refers to proactive actions taken to preserve the efficacy of antimicrobials and emphasizes the prevention of bacterial diseases and use of evidence-based treatment protocols. The ability to broadly implement antimicrobial stewardship in the dairy industry is based on the recognition of appropriate antimicrobial usage as well as an understanding of the benefits of participating in such programs. The most common reason for the use of antimicrobials on dairy farms is the intramammary treatment of cows affected with clinical mastitis or at dry off. Based on national sales data, intramammary treatments comprise < 1% of overall antimicrobial use for food-producing animals, but a large proportion of that usage is a third-generation cephalosporin, which is classified as a highest-priority, critically important antimicrobial. Opportunities exist to improve the use of antimicrobials in dairy practice. While there are barriers to the increased adoption of antimicrobial stewardship principles, the structured nature of dairy practice and existing emphasis on disease prevention provides an opportunity to easily integrate principles of antimicrobial stewardship into daily veterinary practice. The purpose of this paper is to define elements of antimicrobial stewardship in dairy practice and discuss the challenges and potential benefits associated with these concepts.

Survey on the disposal of waste milk containing antimicrobial residues on Swiss dairy farms

Feeding waste milk containing antimicrobial residues (WMA) to calves has been associated with increased antimicrobial resistance in calves' commensal bacterial flora. The objectives of this study were (1) to document practices related to the disposal of WMA on Swiss dairy farms and (2) to evaluate the association between farm characteristics and the feeding of WMA to calves. A web-based questionnaire on practices surrounding waste milk disposal was completed by 1,625 dairy producers (10.9% of solicited producers). Logistic regression models were built to evaluate the association between herd characteristics and the practice of feeding WMA. Waste milk produced during and up to the first milking after completion of antimicrobial treatment or during the withdrawal period was fed to at least some of the calves on 47.3% of respondents' farms. Farms in organic production had lower odds of feeding WMA to calves than nonorganic farms [odds ratio (OR) 0.59]. Farms located in the eastern region of Switzerland, as opposed to those in the western region, had increased odds of feeding WMA to calves (OR 2.01). A yearly average bulk tank somatic cell count ≥150,000 cells/mL was associated with increased odds of feeding WMA to calves compared with the reference category of <100,000 cells/mL (OR 1.62). An average cow-level annual milk production ≥8,500 L was associated with increased odds of feeding WMA to calves compared with farms in the interquartile range with a production of 6,500 to 8,499 L (OR 1.24). Further research is warranted to investigate dairy farmers' motivations affecting this practice, and to quantitatively define calves' exposure to antimicrobial residues and the resulting antimicrobial resistance in calves' commensal flora on these farms.

Evaluation of the use of antibiotic waste bins and medicine records to quantify antibiotic use on sheep, beef, and mixed species farms: A mixed methods study

There is a lack of robust data on antibiotic use on sheep and beef farms in the UK, particularly for farms with mixed species. On mixed farms, quantification of antibiotic use is reliant on accurate farmers' records as veterinary prescription data does not provide information at the species level. Previous studies that have investigated multiple antibiotic use collection methods were conducted on single species farms and failed to collect data on the reasons why differences in methods may exist. This study aimed to evaluate sheep and beef farmers' antibiotic recording practices by comparing quantities of antibiotics measured from medicine records and empty antibiotic packaging collection bins, and identify barriers and facilitators of the antibiotic use collection methods. Thirty-five farms were followed for a year period. Farmers were asked to record their antibiotic treatments and deposit empty antibiotic packaging used in sheep or beef cattle into a bin. Semi-structured qualitative interviews were conducted to understand the experiences of farmers taking part in the study and explore the possible differences in methods. Bins and medicine records were collected and the mass of active ingredient (mg) was calculated. The level of agreement between the two antibiotic use collection methods was measured using rank parameters of Kendall's T_a. The bins were 67 % (CI = 29-87 %) more likely to measure more antibiotic use than the medicine records. The scale of variability of the measurements between two random farms was 33 % (CI = 6-56 %) larger for the antibiotic waste bins than the scale of variability between the medicine records. Sheep farmers often missed neonatal lamb treatments off their medicine records, with a median of 32.5 missing treatments per farm (IQR = 18-130). Of the mixed species farms, 28 % of treatment entries were missing the species the antibiotic was used in. Farmers reported that the bin was easy to use but they also reported that there was a tendency to under-report actual use where there were multiple workers on the farm or where treatments were administered by the veterinarian. The qualitative analysis identified contextual barriers to accurate medicine recording, such as difficulties with animal identification, with recording in the field, and with recording during lambing time. This study demonstrated that there were significant differences in antibiotic use measured by the bins and the medicine records. The mixed-methods approach provided an understanding of the contextual barriers that impacted farmers' medicine recording and use of the bin. This information on the contextual barriers can be used to inform the design of data collection methods to improve antibiotic consumption data in the sheep and beef sectors.

Association between antimicrobial use and antimicrobial resistance of Streptococcus uberis causing clinical mastitis

It is unknown whether overuse of antimicrobials against clinical mastitis (CM) from Streptococcus uberis is associated with increased antimicrobial resistance (AMR). Therefore, the aim of this study was to evaluate the association between antimicrobial use (AMU) and AMR in relation to the Strep. uberis causing CM in dairy herds. A total of 83 Strep. uberis isolates were selected from a collection created during a previous study evaluating the epidemiology of CM in dairy herds (n = 17) of southeastern Brazil. For each case of CM identified on farm, the following information was recorded: cow's identification number, affected mammary quarter, date of CM diagnosis, antimicrobial commercial names, number of administrations, and descriptions of protocol changes during the treatment. Streptococcus uberis isolates were confirmed by conventional culture, MALDI-TOF mass spectrometry, and quantitative multiplex PCR analyses. Thus, a total of 8 antimicrobials commonly used for CM treatment were evaluated for antimicrobial activity against Strep. uberis isolates. The minimum inhibitory levels of antimicrobials were determined at the lowest concentrations able to inhibit 50 and 90%, respectively, of Strep. uberis isolates. Data related to the antibiotics used for treatment of CM was used to calculate the frequency of administered antimicrobials as the number of defined daily doses (DDD). The highest frequencies of resistant Strep. uberis were observed for erythromycin (80.7% resistant, R), tetracycline (R = 59%), and penicillin G (R = 57.8%), whereas against ceftiofur only 10.8% of Strep. uberis isolates were resistant, and only 1.2% of the Strep. uberis isolates were resistant to enrofloxacin. Regarding the evaluation of resistance for antimicrobial classes, the highest frequency was observed for macrolides (R = 80.7%; 19.3% susceptible, S). Additionally, a frequency of 18.7% of Strep. uberis isolates were resistant to cephalosporins (S = 81.3%), respectively. Further, 94% of Strep. uberis isolates were multiresistant; all these isolates presented resistance to at least 3 different antimicrobial classes. The overall monthly average of antimicrobial treatment incidence (ATI) among the 17 herds enrolled in the study was 23.7 DDD per 1,000 lactating dairy cows [standard deviation (SD) = 13.9], ranging from 5.0 to 55.4 DDD per 1,000 cows in lactation-day. Cephalosporins and penicillins were the most commonly used antimicrobial classes among the evaluated herds (n = 16; 94.1%), followed by tetracyclines (n = 15 herds; 88.2%), fluoroquinolones (n = 14; 82.3%), and sulfonamides (n = 14; 82.3%). The tetracycline class had the highest ATI mean (5.0 DDD per 1,000 lactating cow-days, SD = 5.8), followed by fluoroquinolones (4.7 DDD per 1,000 lactating cow-days, SD = 6.0) and cephalosporins (3.8 DDD per 1,000 lactating cow-days, SD = 6.0). The overall use of antimicrobials was associated with the resistance of Strep. uberis to the antimicrobial tetracycline.

From the other perspective: Behavioural factors associated with UK sheep farmers' attitudes towards antibiotic use and antibiotic resistance

Research suggests that many sheep farmers continue to carry out traditional antibiotic use practices despite new ’good practice’ recommendations. The aim of this study was to group farmers depending on their attitudes around antibiotic use and antibiotic resistance, and determine the behaviours that are associated with the farmers in these groups. In 2017, a flock health survey was sent to British sheep farmers. K-means cluster analysis was used to identify groups of farmers with similar attitudes towards antibiotic use and resistance. A multivariable logistic regression model was built to determine the associations between farmers’ past behaviours and their antibiotic attitude group. There were 461 responses. Two groups of farmers were identified based on their antibiotic attitudes. Cluster 1 were defined as the "discordant" group who had positive views of using antibiotics prophylactically and negative views of reducing antibiotic use. Cluster 2 were defined as the "concordant" group who were positive about reducing antibiotic use and had negative views about using antibiotics prophylactically. Using antibiotics in all lambs (OR = 2.689, CI = 1.571, 4.603), using antibiotics in all ewes (OR = 3.388, CI = 1.318, 8.706), always trimming diseased feet over the past three years (OR = 2.487, CI = 1.459, 4.238), not using a computer to record information over the past three years (OR = 1.996, CI = 1.179, 3.381), not changing worming practices over the past three years (OR = 1.879, CI = 1.144, 3.087), and farmers’ perceptions that their sheep flock did not make a financial loss in the past three years (OR = 2.088, CI = 1.079, 4.040) were significantly associated with belonging to the discordant group. Talking to their veterinarian about antibiotic use or the frequency of veterinary visits were not associated with antibiotic attitude group. These results suggest that farmers who had attitudes relating to antibiotic use that did not align with current recommendations carried out more traditional practices, which were strengthened by their positive perceptions of profitability.

Comparison of Quantification Methods to Estimate Farm-Level Usage of Antimicrobials Other than in Medicated Feed in Dairy Farms from Québec, Canada

The objective of the study was to compare three quantification methods to a “garbage can audit” (reference method, REF) for monitoring antimicrobial usage (AMU) from products other than medicated feed over one year in 101 Québec dairy farms. Data were collected from veterinary invoices (VET method), from the “Amélioration de la Santé Animale au Québec” provincial program (GOV method), and from farm treatment records (FARM method). The AMU rate was reported in a number of Canadian Defined Course Doses for cattle (DCDbovCA) per 100 cow-years. Electronic veterinary sales data were obtained for all farms for VET and GOV methods. For the FARM method, a herd management software was used by 68% of producers whereas farm treatment records were handwritten for the others; records could not be retrieved in 4% of farms. Overall, agreement was almost perfect between REF and VET methods (concordance correlation coefficient (CCC) = 0.83), but moderate between REF and GOV (CCC = 0.44), and between REF and FARM (CCC = 0.51). Only a fair or slight agreement was obtained between any alternative method of quantification and REF for oral and intrauterine routes. The billing software used by most of Québec’s dairy veterinary practitioners seems promising in terms of surveillance and benchmarking of AMU in the province.

Antimicrobial use quantification in adult dairy cows - Part 2 - Developing a foundation for pharmacoepidemiology by comparing measurement methods

As stewardship programmes seek to influence therapeutic choices and reduce resistance selection pressure, it is essential to understand the multiple factors which may influence any given antimicrobial use measure. This article compares 9 measures of antimicrobial use pertaining to adult cows in US dairy systems based on treatment records standardized to a single standardized regimen (SReg) format. There are 3 fundamental parameters underlying the nine measures: amount of active substance (AMOUNT), number of SRegs (ANIMALS) and treatment time (TIME). Additionally, three use categories were considered in the analysis: control of mastitis (Dry Cow), treatment of detected mastitis (Clinical Mastitis) and treatment of other diseases (Other Treatment). The assumptions necessary for calculation of each of the nine measures are identified. The influence of measure choice on farm rank was explored at the farm level both within and across fundamental parameters. Across all use categories, when measures of TIME and ANIMALS were compared, correlations between measures were greater than 0.91. However, when measures of AMOUNT were compared to either measures of TIME or ANIMALS, the correlation between measures was more variable across use categories (R = 0.31-0.91). These comparisons demonstrate that the selection of antimicrobial use metric can affect which dairies are considered the highest users of antimicrobials. Measurement selection also influences which use category has the greatest potential for use reduction. This indicates that measure selection can influence which use category is prioritized as a target for reduction of antimicrobial use. Utilization of this information may allow those developing dairy antimicrobial stewardship programmes to better understand the potential effects of measurement selection on driving changes in antimicrobial use.

Reducing Antimicrobial Use by Implementing Evidence-Based, Management-Related Prevention Strategies in Dairy Cows in Switzerland

The aim of this study was to reduce antimicrobial use (AMU) on dairy farms that implemented evidence-based management strategies. The study not only examined whether these strategies led to a reduction in AMU in practice, but also examined the influence of the level of their implementation on AMU. For data analysis, practice software recordings of the farm veterinarians were used. The AMU data of 50 farms with prevention strategies applied (intervention group, IG) over 3 years (2017–2019) and of 74 farms without prevention strategies (control group, CG) over 2 years (2018–2019) were analyzed. Project participation was supported with 500 Swiss francs (~545 USD) per farmer per year. The AMU was compared between the IG and CG using the treatment incidence. In December 2017/January 2018, the farmers of the IG had chosen at least one of the proposed 17 prevention strategies from one of three sectors, i.e., udder health, uterine health and/or replacement calf health. The prevention strategies, were developed in a standard operating procedure protocol and were discussed in detail with the farmers before the implementation. Forty-eight farms chose at least one udder strategy, 10 farms at least one uterine strategy and 37 farms at least one calf strategy. By choosing an udder health strategy or a uterine health strategy, the corresponding systemically administered AMU could be significantly reduced (p < 0.04) in the IG compared with the CG. In addition, udder strategies that were well-implemented led to a significant reduction (p = 0.05) of intramammary “highest priority critically important antimicrobials (HPCIA)” (quinolones, cephalosporins 3rd and higher generation, macrolides and ketolides, glycopeptides, and polymyxins). The level of implementation was significantly lower in 2019 compared to 2018 (p < 0.05, Fisher's exact test). No significant reduction in AMU could be achieved for the calf sector. A reduction of AMU in dairy farms is possible by implementing evidence-based management-related prevention strategies. The level of implementation has only an influence on the consumption of HPCIA. The reduction of AMU in practice by means of evidence-based measures requires supportive human resources instead of financial support, because financial support for farmers seems not to motivate them sufficiently.

Antimicrobial consumption: Comparison of three different data collection methods

The increasing incidence of antimicrobial resistance represents a global threat. As a result, surveillance programmes monitoring antimicrobial consumption and resistance in animals have been implemented in several countries throughout the world. However, such programmes depend on the accurate and detailed collection of data on antimicrobial consumption. For this reason, the aim of this longitudinal study was to compare the consistency of data on antimicrobial consumption between three different data collection methods. Antimicrobial consumption data associated to udder health were collected from 20 veterinary practices and 92 dairy farms for 18 months. The compared data sources were: 1) data extracted from veterinary practice software 2) farm treatment journals and 3) on-farm discarded drug packages (garbage). Two different procedures were chosen to analyse the data issued from treatment journals: 1) only complete entries were analysed 2) entries with missing dosage were supplemented with the information provided by the Swiss Compendium of Veterinary Medicinal Products. The antimicrobial data were divided into intramammary preparations used during lactation (IMM), intramammary preparations used for dry off (DRY) and systemic treatments (SYS). We compared the quantities of injectors (IMM and DRY), the quantities of active substances (SYS) and the treatment incidences (TI) for the defined daily dose (DDD) per 1000 cow-days (IMM and SYS) and the defined course dose (DCD) per 1000 cow-days (DRY). Additionally, the variety of antimicrobial products among the different data sources was compared. The highest quantity of antimicrobials for IMM, DRY and SYS could be collected with the software data. The lowest quantity was collected by using the data of the treatment journal with only complete entries. For IMM and DRY, software and garbage performed similar, with agreement on the number of injectors used in 56.1% of the analysed cases. The widest variety of intramammary antimicrobial preparations was found in the garbage whilst most systemic preparations were collected using software data. The results of the study show a lack of data consistency between the three different data sources. None of the methods was able to collect the integral antimicrobial consumption in the participating farms. Finally, the results emphasise the need to implement a standardised system to quantify and assess the antimicrobial consumption at veterinary practice and farm level.

An observational cohort study on antimicrobial usage on dairy farms in Quebec, Canada

Quantification of antimicrobial usage (AMU) is crucial to measure the effect of intervention programs, to determine associations between usage and resistance, to compare populations, and for benchmarking purposes. The primary objective of the study was to describe quantitatively the AMU on Quebec dairy farms over 1 yr: (1) the total AMU, (2) the AMU per administration route (intramammary, injectable, oral, intrauterine), and (3) the AMU per antimicrobial class and according to the categorizations of Health Canada and the World Health Organization. The secondary objective was to assess the effect of several characteristics (herd size, level of milk production, and incidence rate of common infectious diseases) on AMU rate. The AMU data were obtained for 101 dairy farms randomly selected in 3 important Quebec dairy regions by collecting and recording all empty drug packaging and invoices for medicated feed (spring 2017 to spring 2018). The AMU rate was reported in number of Canadian defined course doses for cattle per 100 cow-years. The average herd size was 67 cows per farm, and 2/101 farms were certified organic. Overall, an estimated mean of 537 Canadian defined course doses for cattle/100 cow-years was observed. The intramammary route during lactation was the most frequently observed, followed, in decreasing order of usage, by oral route in the feed, intramammary route at drying-off, and injectable route. Oral (other than in animal feed) and intrauterine formulations were infrequently collected from the garbage cans. The 5 most frequently observed antimicrobial classes were, by decreasing order of usage, ionophores, penicillins, aminocoumarins, aminoglycosides, and polymyxins. Highest priority critically important antimicrobials as defined by the World Health Organization were mainly collected from intramammary formulations during lactation followed by injectable and drying-off intramammary formulations. The herd size was positively associated with the total AMU rate but not with the usage rate of highest priority critically important antimicrobials. Incidence of diseases along with preventive use of antimicrobials (drying-off and medicated feed with antimicrobials) explained 48% of the variance in total AMU rate.

First Case Report on Quantification of Antimicrobial Use in Corporate Dairy Farms in Pakistan

Intensive livestock farming has become indispensable to meet the rapidly increasing demand for animal-based nutrition in low- and middle-income countries (LMICs) where antimicrobials are frequently used for treatment and prophylactic or metaphylactic purposes. However, very little is known about the trends of antimicrobial use (AMU) in dairy animals in LMICs. The objective of this study was to quantify AMU in two large commercial dairy farms in Pakistan. A retrospective study was conducted at two large corporate commercial dairy farms located in Punjab province for the year 2018. AMU was calculated using three metrics: active ingredient (AI; kg) and milligrams per population unit (mg/PU; mg/kg), which quantifies the amount of AI used, and antimicrobial treatment incidence (ATI; DDDA/1,000 cow-days), which estimates the per-day number of treatments to 1,000 cows. Total on-farm AMU was found to be 138.34 kg, 65.88 mg/kg, and 47.71 DDDA/1,000 cow-days. Measured in ATI, aminoglycosides (11.05 DDDA/1,000 cow-days), penicillins (8.29 DDDA/1,000 cow-days), and tetracyclines (8.1 DDDA/1,000 cow-days) were the most frequently used antimicrobial classes. A total of 42.46% of all the antimicrobials used belonged to the critically important antimicrobials for human medicine as defined by the World Health Organization. Considerably high AMU was found compared to other farm-level studies across the world. This was the first study to quantify AMU in the dairy industry in Pakistan. Our results showed that corporate commercial dairy management practices are associated with increased antimicrobial consumption and highlight the need for antimicrobial stewardship programs to encourage prudent use of antimicrobials in commercial dairy.

Evaluation of the antimicrobial use in pigs in Japan using dosage-based indicators

The use of antimicrobial agents in food-producing animals may lead to the emergence and spread of antimicrobial resistance in bacteria of animal origin. The use of antimicrobial agents in pigs in 2018 in Japan was evaluated in terms of the weight of active ingredient and number of defined daily doses (DDD), using annual sales data of veterinary antimicrobials sold for use in pigs. In addition, the use of antimicrobial agents in the Japanese pig sector in 2008 to 2017 was evaluated to determine whether or not there were any differences in temporal change pattern by use of different metrics. In 2018, 447 metric tons of active ingredient, corresponding to 77,379 × 106 kg-days (Japanese DDD) and 34,903 × 106 kg-days (European DDD) were sold. The proportion of the sales amount of sulfonamides, trimethoprim and lincosamides to the total sales amount was significantly different depending on the metric used. For most antimicrobial classes, the number of Japanese DDDs was greater than the number of European DDDs. These results indicate that the DDD-based metric, which is more reflective of the selective pressure of antimicrobials, is recommended for use in monitoring the antimicrobial use in pigs in Japan. The differences in the number of Japanese DDDs and European DDDs appear to confirm the need for Japanese DDDs.

Antibiotic Consumption on Dairy and Beef Cattle Farms of Central Italy Based on Paper Registers

The overuse of antibiotics in livestock contributes to the antibiotic resistance pandemic. The assessment of the actual antibiotic consumption is crucial in limiting the expansion of the problem effectively. The aim of this study was to provide the first qualitative and quantitative analysis of antimicrobial usage using data from paper-based registers on dairy and beef farms located in the Umbria region, Italy. Antimicrobial therapies of a one-year period were collected from 101 farms with at least 50 cattle each. Defined daily doses (DDDvet) and defined course doses (DCDvet) were calculated per administration route and antimicrobial class. The total courses administered were fewer in beef (330.7 × 10-3 DCDvet/year) than in dairy farms (1034.1 × 10-3 DCDvet/year). The use of the highest priority critically important antimicrobials (HPCIAs) was higher (p = 0.0033) in dairy than in beef herds. In terms of DDDvet, the parenteral fluoroquinolone administration ranked second and fourth on dairy and beef farms, respectively; the consumption of beta-lactams was ten times higher on dairy than on beef farms. Our results confirm that intensive dairy management practices are associated with increased antibiotic consumption and highlight the necessity to strengthen the existing stewardship programs by involving all stakeholders in effective antimicrobial resistance reduction plans.

Knowledge, attitude and practices of Swiss dairy farmers towards intramammary antimicrobial use and antimicrobial resistance: A latent class analysis

Understanding farmers' mindsets is important to improve antimicrobial stewardship in the dairy industry. This cross-sectional study aimed to determine farmers' knowledge, attitude, and practices with respect to lactational intramammary antimicrobial use (AMU) and antimicrobial resistance (AMR) in Swiss dairy herds. Based on their approach towards subclinical mastitis (SCM) and non-severe cases of clinical mastitis (CM), subgroups of farmers were identified and compared regarding their knowledge, attitude and practices towards AMU and AMR. After conducting qualitative interviews to develop a questionnaire, an online survey was sent to 1296 randomly selected Swiss dairy farmers. Information was gathered on demographic data and farmers' knowledge, attitude, and practices towards AMU and AMR. A latent class analysis was performed to identify subgroups of farmers based on management of SCM and non-severe CM cases. Based on the results of 542 completed questionnaires, poor knowledge with respect to AMU and AMR was identified, as well as discrepancies between farmers' perceptions and their actual practices. Farmers approached cows with SCM and non-severe CM similarly, indicating they perceived both mastitis states as the same disease. Intramammary antimicrobial products containing cefquinome, which is a highest priority critically important antimicrobial, were among the 3 most commonly applied intramammary antimicrobials. Five latent classes of farmers were identified based on their management towards SCM and non-severe CM. One group of farmers (18.5% of respondents) indicated that they did not treat those mastitis cases, one group only treated SCM cases (13.8% of respondents), one group only treated non-severe CM cases (28.6% of respondents) and the largest group treated both mastitis states (39.1% of respondents). The latter group was subdivided into a latent class of farmers following guidelines for AMU/AMR (25.5% of respondents) and a group of farmers that were not strictly following these guidelines (13.7% of respondents). Regional differences between farmers, according to altitude and language region, explained some of the variation in latent class membership. Latent class membership was associated with farmers' attitude to use antimicrobials as little as possible and with using antimicrobials only after performing bacteriological and susceptibility testing. This study gave detailed insight into Swiss farmers' knowledge, attitude, and practices regarding AMU and AMR and provides opportunities to improve antimicrobial stewardship in Swiss dairy herds. The identified groups of farmers, based on their management practices regarding SCM and non-severe CM, may help to design tailored intervention strategies for improving prudent AMU in the heterogeneous population of dairy farmers in Switzerland.

Comparison of animal daily doses and days of therapy for antimicrobials in species of veterinary importance

Characterizing antimicrobial use in animal populations is critical for purposes of antimicrobial stewardship. While dose-based metrics such as the animal daily dose (ADD) are typically used for such purposes, duration of therapy is emerging as a critical and more intuitive metric. In theory, the number of ADDs should approximate the number of days of therapy (DOTs), but no studies have examined whether this is the case. The objective of this study was to compare antimicrobial ADDs with antimicrobial DOTs in three populations: canine patients, large animal hospital patients, and dairy herds. In the first two populations, dose-based metrics were calculated using administrative hospital records while duration-based metrics were ascertained from manual chart review of individual animals. In the dairy herds, both metrics were obtained via farmer self-report. We found that the correlation between the number of ADDs and DOTs was poor for hospital patients (Lin correlation coefficients of 0.16 and 0.18 for small and large animals, respectively) and that there were often large differences between the two metrics for all populations, with ADDs most often overestimating the number of DOTs. While the median (IQR) differences between the number of DOTs and ADDs were relatively small (-9.4 (-25.7-(-0.92)), 0.34 (-5.0-4.0), and 0.0 (-18.0-9.0) among canine patients, large animal hospital patients, and dairy herds, respectively), the limits of agreement (-89.4-13.2, -37.7-9.9, and -100.0-53.0, respectively) were likely too large to be acceptable for most investigative purposes. Increased discrepancies between the two metrics were significantly associated with certain animal species (e.g., dogs, small ruminants) and drug classes (e.g., penicillins, cephalosporins, macrolides), decreased animal weight, and increased length of hospital stay. While the number of ADDs can approximate the number of DOTs under certain circumstances, the large limits of agreement between these two measurements suggest that the ADD is generally not a reliable proxy for the duration of therapy.

Antimicrobial use for treatment of clinical mastitis in dairy herds from Brazil and its association with herd-level descriptors

The aims of this prospective and descriptive study were to: (a) characterize treatment profile and quantify antimicrobial consumption for treatment of clinical mastitis (CM) in dairy herds of Brazil; and, (b) determine the association of antimicrobial use (AMU) for treatment of CM and herd-level descriptors, such as herd size, average milk yield, bulk milk somatic cell count (BMSCC), bulk milk total bacterial count (BMTBC), season and housing type. Data on treatment practices were obtained from 19 of 20 dairy herds selected for the study for a period of 12 months per herd. Treatment protocols were recorded in each case of CM by the farm personnel using a form that included information at the cow- and treatment-level. The frequency of antimicrobial consumption for treatment of CM was determined monthly in units of defined daily dose (DDD) and expressed as antimicrobial treatment incidence (ATI; the number of DDD per 1,000 lactating cow-days). Mixed linear regression models were used to determine the association between log-transformed ATI and herd level descriptors. The overall monthly mean ATI was 21.9 DDD per 1,000 lactating cow-days (15.4 DDD per 1,000 lactating cow-days for intramammary compounds, and 6.4 DDD per 1,000 lactating cow-days for systemically administered antimicrobials). Among intramammary drugs, aminoglycosides had the highest ATI (11.7 DDD per 1,000 lactating cow-days), followed by a treatment with a combination of tetracycline, aminoglycoside and polypeptide (10.3 DDD per 1,000 lactating cow-days). For systemically administrated antimicrobials, fluoroquinolones (6.1 DDD per 1,000 lactating cow-days), penicillin combinations (3.9 DDD per 1,000 lactating cow-days), and the combination of sulfonamide and pyrimidine (3.6 DDD per 1,000 cows per day) were the most frequently used antimicrobials. The use of combination therapy (i.e., association of intramammary and systemically administered antimicrobials) was reported for 64.3 % of treatments at the cow-level. The AMU tended to be higher in herds with highest BMSCC. In addition, a higher AMU for treatment of CM was observed during the rainy season compared to the dry season in Brazil. This seasonal effect was mostly characteristic in herds housing cows in outdoor housing systems (i.e., paddocks).

Assignment of Canadian Defined Daily Doses and Canadian Defined Course Doses for Quantification of Antimicrobial Usage in Cattle

Standardized units are essential to allow quantification and comparison of antimicrobial usage (AMU) between species and regions. In Canada, defined daily and course doses have not yet been harmonized for cattle. Our objective was to assign defined daily and course doses (named DDDbovCA and DCDbovCA, respectively) for cattle in Canada, by antimicrobial agent (AM) and by route of administration, based on the label of all products containing at least one AM, marketed and authorized in Canada for use in cattle. In April and December 2019, a systematic search was performed from the online Drug Product Database (DPD) of Health Canada to identify veterinary products containing at least one AM, marketed in Canada for use in cattle. Products were divided by route of administration (intramammary, intrauterine, injectable, oral, and topical). The monograph was retrieved for each product from the DPD, or from the Canadian Edition of the Compendium of Veterinary Products (CVP), and read completely to extract recommended dosages in cattle. Standard weights were applied to compute doses if required. DDDbovCA and DCDbovCA were assigned by calculating an average of daily and course doses, respectively, by AM and route of administration. Two products were excluded from calculations because of their claim as growth promotion or feed efficiency (no longer authorized in Canada for certain categories of AM). Overall, 39 injectable, 75 oral (including 23 medicated premixes), 8 intramammary (4 for lactating cows and 4 for dry cows), 5 intrauterine, and 4 topical products were used for calculations. DDDbovCA and DCDbovCA values were assigned successfully for each AM identified, by route of administration. These metrics will allow harmonized and transparent quantification of AMU in cattle in Canada.

Do Dairy Farming Systems Differ in Antimicrobial Use?

Simple Summary

The overuse and misuse of antimicrobials in dairy farming may lead to the development of antimicrobial resistance and thus to the reduction of the antimicrobial treatment efficacy against animal or human bacterial diseases. This study aims to investigate antimicrobial use differences in four farm groups: mountain farms with specialized high-yield dairy breeds or with dual-purpose breeds raised for milk production, and lowland farms with specialized high-yield dairy breeds or with dual-purpose breeds raised for milk production. From the results, we found a significant difference between mountain farms with dual-purpose breeds and lowland farms with specialized breeds for the overall antimicrobial use and for the use of those antimicrobial classes that are most important in human medicine. Mountain farms have a generally lower milk production and smaller herd size than lowland farms, provide cows with access to pasture, and limit concentrates in the diet. These management practices and the use of local/dual-purpose breeds could reduce the risk of production diseases and the consequent need for antimicrobial use.

Abstract

The quantitative assessment of antimicrobial use (AMU) in food-producing animals contributes to the provision of essential information for developing relevant and effective policies to reduce use and to control antimicrobial resistance. Information on AMU is available mainly for intensive dairy farming systems and specialized high-yielding breeds. The aim of this study is to investigate AMU in different dairy farming systems by comparing the treatment incidence in mountain farms with specialized high-yield dairy breeds or with dual-purpose breeds raised for milk production to the treatment incidence in lowland farms with specialized high-yield dairy breeds or with dual-purpose breeds raised for milk production. Significant differences were found only between the overall treatment incidence, as well as the treatment incidence of highest-priority critically important antimicrobials for human medicine, in lowland farms with high-yielding breeds and mountain farms with dual-purpose breeds. Mountain farms have a generally lower milk production and smaller herd size than lowland farms, provide cows with access to pasture, and limit concentrates in the diet. These management practices and the use of local/dual-purpose breeds could reduce the risk of production diseases and the consequent need for AMU.

Sales data as a measure of antibiotics usage: Concepts, examples and discussion of influencing factors

Monitoring and surveillance of antimicrobial usage in animals is a public health concern and different methods are currently discussed widely in public, science and politics. The objective of the paper is to present the available methods of monitoring and to discuss possible differences in the assessment of the antibiotics treatment. Sales data are expressed as the average amount of substance per animal or kg live weight (e.g. population‐corrected unit, PCU). The number of Defined Daily Doses (nDDDvet) is calculated by extrapolating sales data with average animal weights and defined drug doses to a number of treatments theoretically applied to animals. In contrast, the number of Used Daily Doses (nUDDvet) displays the actual number of treatments which have been applied. As sales data are relatively easily obtained, they are frequently used. However, their results are influenced by the composition of the population and by the dose of the substances. As both may vary strongly between countries, direct comparison of sales data between countries may be misleading. The concept of analysing sales data is shown by exemplarily using the methods in the ESVAC report 2015. The presentation of usage data in terms of nDDDvet or of nUDDvet increases the comparability of the data from different countries or time periods. Furthermore, fluoroquinolones and third‐/fourth‐generation cephalosporins which, among other substances, bare a potential risk for human health, are used at low doses. Hence, their use contributes to a sales reduction while contrasting the guidelines of prudent use. nDDDvet or nUDDvet have the ability to better reflect the treatment frequency and thus to better link antibiotics use to public health concerns. Quantification of antibiotics should assist to focus on prudent use of antimicrobials to reduce the burden of resistant bacteria and, thus, enhance public health, animal health and animal welfare.

Data-driven approach to using individual cattle weights to estimate mean adult dairy cattle weight

BACKGROUND

Knowledge of accurate weights of cattle is crucial for effective dosing of individual animals and for reporting antimicrobial usage. For the first time, we provide an evidence-based estimate of the average weight of UK dairy cattle to better inform farmers, veterinarians and the scientific community.

METHODS

Data were collected for 2747 lactating dairy cattle from 20 farms in the UK. Data were used to calculate a mean weight for lactating dairy cattle by breed and a UK-specific mean weight. Trends in weight by lactation number and production level were also explored.

RESULTS

Mean weight for adult dairy cattle in this study was 617 kg (sd=85.6 kg). Mean weight varied across breeds, with a range of 466 kg (sd=56.0 kg, Jersey) to 636 kg (sd=84.1, Holsteins). When scaled to UK breed proportions, the estimated UK-specific mean weight was 620 kg.

CONCLUSION

This study is the first to calculate a mean weight of adult dairy cattle in the UK based on on-farm data. Overall mean weight was higher than that most often proposed in the literature (600 kg). Evidence-informed weights are crucial as the UK works to better monitor and report metrics to measure antimicrobial use and are useful to farmers and veterinarians to inform dosing decisions.

Veterinary peer study groups as a method of continuous education-A new approach to identify and address factors associated with antimicrobial prescribing

Within the dairy industry, most antimicrobials are used for dry-cow therapy or mastitis treatment. To reduce antimicrobial usage in dairy cows, increasing awareness and behaviour change is necessary. As veterinarians are known to be influenced by their peers, peer study groups as a continuous education might contribute to this. Therefore, the objective of this study was to analyse written records of veterinary peer study group meetings to identify factors associated with antimicrobial prescribing decisions, and to analyse veterinarians' attitude towards the benefits of this continuous education method. Twenty-three participating Swiss cattle practitioners were divided into three groups. Each group met every two to five months, together with a facilitator and an expert on the topic to be discussed. Written records from every meeting were taken and analysed qualitatively to identify factors influencing veterinarians' decisions on antimicrobial prescribing and mastitis therapy. In addition, focus group discussions were conducted after the last meeting, to assess the veterinarians' learning achievements gained during the peer study group meetings. Extrinsic factors such as external pressure, competition, farmer, individual animal, farm and diagnostics as well as intrinsic factors such as own experience/attitude, knowledge and change of mindset during career could be shown to influence veterinarians' decisions on antimicrobial prescribing. In the focus group discussions, the veterinarians stated that they gained new knowledge, received new stimuli, exchanged with their peers and felt supported in their relationship to their farmers. Since the identified factors are partly interrelated, it is not sufficient to change a single factor to achieve a change in the antimicrobial prescription behaviour of veterinarians. Veterinary peer study groups could contribute to the intention to change, because veterinarians experienced multiple benefits from this method of continuous education. In order to quantify this, the prescription data of the veterinarians are analysed in a next step.

Monitoring Antibiotic Usage in German Dairy and Beef Cattle Farms-A Longitudinal Analysis

It is well-established that antimicrobial use is a major factor for the development of antimicrobial resistance. To analyze the associations between antimicrobial resistance and usage of antimicrobial agents, data from monitoring and surveillance systems are crucial. Within the project VetCAb (Veterinary Consumption of Antibiotics), antibiotic usage data in German livestock is regularly collected and evaluated. Based on a cross-sectional study in 2011, the project was continued as the longitudinal study VetCAb-Sentinel with ongoing participant recruitment and data collection from 2013. The data collection is based on official German application and delivery forms (ADF), voluntarily provided by veterinarians and farmers. In this study the results of antibiotic usage data of dairy cows, dairy calves and beef cattle were described, using a semi-annual treatment frequency, and 95,944 ADF issued between 2011 and 2015 were analyzed. Results show that the median of the treatment frequency in dairy calf and beef cattle holdings slightly decreased from 0.4 to 0.3 and from 0.2 to 0 days, respectively, whereas the median in dairy cow holdings ranged between 1.9 and 2.3 during the observed period. Temporal changes and the effect of the factors "farm size" and "region" on the treatment frequency were investigated, using multiple linear mixed and logistic regression models. Generally, the factor "time" has a statistically significant impact on the treatment frequency in all production types. In addition, a temporal trend test over the first six half-years shows that an increasing linear trend can be stated in dairy cows and dairy calves (p = 0.017; p = 0.004, respectively). If the time-period is extended to all eight half-years under study, this turns into a quadratic effect (dairy cows: p = 0.006; dairy calves: p < 0.001). In dairy calves and beef cattle the factor "farm size" also has a statistically significant impact. The factor "region," in contrast, shows no statistically significant impact at all. Compared to other livestock populations in Germany, the use of antimicrobials in dairy cows, dairy calves, and beef cattle appears to be low, but varies across several associated factors. Considering these effects, it is recommended that the size of dairy calf and beef cattle holdings is regularly considered in the evaluation of antimicrobial usage data over time.

Aetiology and prevalence of subclinical mastitis in dairy herds in peri-urban areas of Kigali in Rwanda

The aim of this cross-sectional study was to evaluate the prevalence of subclinical mastitis (SCM) and associated risk factors in dairy cows in peri-urban areas of Kigali, Rwanda, and identify causative udder pathogens. A sample of 256 cows from 25 herds was screened with the California Mastitis Test (CMT), and udder quarters with CMT score ≥ 3 (scale 1–5) were milk sampled for culture and final bacteriological identification with matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). All resultant staphylococci species were tested for beta-lactamase production with the clover leaf method. In parallel, herd bulk milk somatic cell count (SCC) of each herd was analysed using a portable device, the DeLaval cell counter. The prevalence of SCM was 43.1% at quarter level and 76.2% at cow level based on CMT test. Multiparous, Holstein cows were 2.50 (C.I = 1.32–4.71) and 10.08 (C.I = 1.54–66.13) times more likely to contract SCM infection than primiparous animals or cows of other breeds, respectively. The median and mean SCC of all herds were 1108 × 10³ cells/mL and 1179 × 10³ cells/mL, respectively. The most prevalent pathogens were non-aureus staphylococci (NAS; 40.2%) followed by Staphylococcus aureus (22%) and less prevalent pathogens (6%). Samples with no growth or contamination constituted 30.4% and 1.4% of the diagnoses, respectively. The most prevalent species within NAS were S. epidermidis (38.2%) followed by S. sciuri (19.5%), S. chromogenes (9.8%), and nine less prevalent NAS species (32.5%). Out of 209 staphylococci isolates, 77% exhibited beta-lactamase production. The study shows that there is high prevalence of SCM and high herd bulk milk SCC in herds in Kigali, indicating udder health problems in dairy cows. Additionally, beta-lactamase production among staphylococci species was common. Improved milking hygiene and application of biosecurity measures, or a complete mastitis control plan, is required to lower the prevalence of SCM and minimize the spread of pathogens among dairy cows.

Effects of management practices, animal transport and barn climate on animal health and antimicrobial use in Swiss veal calf operations

To assess the effects of transport, management factors and barn climate on calf health, 43 Swiss veal farms (11 large farms fattening ≥100 calves and 32 small farms fattening >20 but <100 calves per year) were monitored in a prospective cohort study over a period of one year. Detailed questionnaires on farm structure, management, housing system and animal health were filled out with the farmers during bimonthly visits, and barn temperature, humidity, ammonia and CO₂ concentrations were measured. Temperature and humidity were also measured continuously over 72 h once each in winter and summer. In addition, calf purchase and transport from birth farm to fattening unit were documented by the farmers, and the study team accompanied one transport per farm whenever possible. Antimicrobial treatment incidence was calculated from the used daily dose (TI_UDD). Risk factors for mortality, average daily weight gain (ADG) and antimicrobial use, as well as factors related to transport and barn climate measures were evaluated with mixed regression models. The overall mortality rate was 5.1% (6.2% in large herds and 3.1% in small ones). Identified risk factors for mortality >3% included a lower number of calves fattened per year and a good hygiene of the feeder. This surprising result was likely due to the fact that the threshold of 3% mortality was rather exceeded in smaller farms. Furthemore, higher temperature variation (range between maximal and minimal temperature over 3 measurement days) in the calf pen was associated with mortality >3% in the univariable analysis. The overall mean ADG was 1.40 ± 0.16 kg. Calf purchase was significantly associated with decreased ADG. The median overall TI_UDD was eight daily doses per calf and year (2.1 in small farms and 26 in large farms, respectively); the main indication for treatment was respiratory disease (81.1%). Risk factors for increased TI were no quarantine upon arrival, access to an outside pen, higher numbers of calves per drinking nipple, mechanical ventilation, vaccination against bovine respiratory disease, and a maximum ammonia value >10 ppm in the calf pen. In addition, a higher number of birth farms and calf purchase from markets were associated with increased TI in the univariable analysis. The identified risk factors associated with increased TI and mortality and with decreased ADG should be addressed in priority in veal calf operations to improve calf health and reduce antimicrobial use.

Storage of prescription veterinary medicines on UK dairy farms: a cross-sectional study

Prescription veterinary medicine (PVM) use in the UK is an area of increasing focus for the veterinary profession. While many studies measure antimicrobial use on dairy farms, none report the quantity of antimicrobials stored on farms, nor the ways in which they are stored. The majority of PVM treatments occur in the absence of the prescribing veterinarian, yet there is an identifiable knowledge gap surrounding PVM use and farmer decision making. To provide an evidence base for future work on PVM use, data were collected from 27 dairy farms in England and Wales in Autumn 2016. The number of different PVMs stored on farms ranged from 9 to 35, with antimicrobials being the most common therapeutic group stored. Injectable antimicrobials comprised the greatest weight of active ingredient found, while intramammary antimicrobials were the most frequent unit of medicine stored. Antimicrobials classed by the European Medicines Agency as critically important to human health were present on most farms, and the presence of expired medicines and medicines not licensed for use in dairy cattle was also common. The medicine resources available to farmers are likely to influence their treatment decisions; therefore, evidence of the PVM stored on farms can help inform understanding of medicine use.

The effect of mastitis management input and implementation of mastitis management on udder health, milk quality, and antimicrobial consumption in dairy herds

The main objective of this study was to evaluate evolutions in herd-level antimicrobial consumption (AMC) and in udder health and milk quality parameters between herds that received mastitis management input on a regular basis (actively advised by the first author; referred to as intervention herds) and herds that did not (referred to as control herds). Strikingly, herds in the intervention group had a significantly higher prevalence of new intramammary infections compared with those in the control group. No significant differences were observed in the percentage of chronically infected cows, the bulk milk somatic cell count, and the bacterial and coliform count between the intervention and control herds, nor did the herd-level AMC differ between them. Furthermore, the level of mastitis management applied in each herd was assessed and scored [mastitis management score (MMS); higher is better], as was the level of implementation of different recommended mastitis management practices over time, expressed as the mastitis management implementation score (MMIS; higher is better). A large variation was observed in MMS and MMIS in the intervention herds (median = 16 and range = 12 to 22; median = 13 and range = -5 to 31, respectively) and the control herds (median = 16 and range = 9 to 22; median = 9 and range = -13 to 22, respectively). Also, intervention herds in which the herd veterinarian attended each herd visit executed by the first author had a higher MMS and MMIS (median = 20 and 24, respectively) compared with herds in which the veterinarian sometimes (median = 16 and 17, respectively) or never (median = 16.5 and 7.5, respectively) attended the herd visits. Further, the association between MMS or MMIS on one hand and udder health, milk quality, and the herd-level AMC over time on the other was studied using the data of both groups of herds. Better mastitis management was associated with a reduction in the consumption of antimicrobials that are critically important for human health over time and with lower bacterial counts and bulk milk somatic cell count. Better mastitis management can be helpful in obtaining better milk quality and more responsible use of critically important antimicrobials on dairy farms.

Quantification of antibiotic use on dairy farms in Pennsylvania

Antibiotic use data are critical for drawing conclusions about the epidemiological connections between antibiotic use in farms animals, antibiotic resistance, animal health, and human health. The goal of this study was to quantitatively and qualitatively characterize antibiotic use on dairy farms in Pennsylvania, the state with second largest number of dairy farms nationally. A survey was sent to 10% of the 6,580 dairy farms registered in Pennsylvania and completed by 235 producers (response rate of 36%). Data on antibiotic use in the previous month and in the previous 6 mo were collected based on farmer self-report, using either recall or treatment records. Two metrics were used to quantify antibiotic consumption: animal-defined daily doses (ADD) and days of therapy (DOT), a metric used in human medicine for purposes of antimicrobial stewardship. Across all farms, 24,444 ADD and 19,029 DOT were reported, representing treatment incidences of 4.2 ADD/1,000 animal-days and 3.3 DOT/1,000 animal-days. These rates were generally lower than those found in other states and countries. The main indication for antibiotic use was mastitis, and first-generation cephalosporins were the most commonly used class of antibiotic for all indications, followed by penicillins and third-generation cephalosporins. Trends in use were similar for ADD and DOT, but the numbers of recorded DOT and associated treatment incidences were generally lower than the number of ADD and associated treatment incidences. Rates of treatment were significantly associated with herd size. This study is the first to quantify antibiotic use on dairy farms in Pennsylvania and the first to use the DOT metric in a dairy setting.

Antimicrobial Usage in Animal Production: A Review of the Literature with a Focus on Low- and Middle-Income Countries

Antimicrobial use (AMU) in animal production is a key contributor to antimicrobial resistance (AMR) worldwide. As consumption of animal protein and associated animal production is forecast to increase markedly over coming years in low- and middle-income countries (LMICs), accurate monitoring of AMU has become imperative. We summarized data from 89 scientific studies reporting AMU data in animal production published in English since 1998, identified through the 'ISI Web of Knowledge' search engine. The aims were as follows: (a) to describe methodologies and metrics used to quantify AMU; (b) to summarize qualitative (on-farm prevalence of use) and quantitative (amounts of antimicrobial active principle) data, in order to identify food animal species at the highest risk of AMU; and (c) to highlight data gaps from LMICs. Only 17/89 (19.1%) studies were conducted in LMICs. Sixty (67.3%) reported quantitative data use, with 'daily doses per animal-time' being the most common metric. AMU was greatest in chickens (138 doses/1000 animal-days [inter quartile range (IQR) 91.1⁻438.3]), followed by swine (40.2 [IQR 8.5⁻120.4]), and dairy cattle (10.0 [IQR 5.5⁻13.6]). However, per kg of meat produced, AMU was highest in swine, followed by chickens and cattle. Our review highlights a large deficit of data from LMICs, and provides a reference for comparison with further surveillance and research initiatives aiming to reduce AMU in animal production globally.

Factors associated with high antimicrobial use in young calves on Dutch dairy farms: A case-control study

Since 2012, the Dutch Veterinary Medicine Authority reports antimicrobial usage (AMU) in young calves (<56 d) on dairy farms on an annual basis. The AMU distribution in this age group is skewed, with a low AMU in young calves on the majority of dairy farms and a high AMU in a relatively small number of farms. This results in a notable difference between the mean and median AMU. To further reduce the mean AMU, the AMU on the high-AMU farms must be decreased. The objective of this study was to evaluate the association between both young stock management and an indication of the farmers' mindset and AMU in young calves on Dutch dairy farms with a high and low AMU in young calves. This knowledge may be helpful in decreasing AMU in young calves on high-AMU farms. We performed a case-control study in which 200 dairy farms (100 with high AMU and 100 with low AMU in young calves) participated. Case farms were defined as farms with an animal daily-defined dose at the farm level in young calves >28 in 2012 and 2013, based on the 90th percentile of the use of antimicrobials in young calves in 2012. Control farms had an animal daily-defined dose at the farm level in young calves of <0.5 in 2012 and 2013, which was determined to be low use. A questionnaire was conducted about general farm and young stock management, hygiene, housing, vaccination, and calf health. An indication of the farmers' mindset with regard to AMU and treatment of sick calves was determined by including statements (agree/disagree) in the questionnaire. In addition, routinely collected data on herd size, growth in herd size, replacement, and calf mortality were available for analysis. Dairy farmers that immediately started antimicrobial treatment in sick calves had higher odds of being in the high-AMU group than farmers who started treatment of sick calves with supportive nonantimicrobial therapy. Other variables associated with a high AMU in young calves included housing calves on partially slatted floors, a high prevalence of respiratory disease, an unfavorable Salmonella status, and not agreeing with the statement "Young stock need specific management." Both dairy farm management and opinions of dairy producers regarding AMU, indicative of mindset, are important when distinguishing farms with high and low AMU in young calves. Although the rationale behind mindset warrants more research, likely a change in both aspects seems to be required to reduce the AMU in young calves on dairy farms.

Risk Ranking of Antimicrobial-Resistant Hazards Found in Meat in Switzerland

Human exposure to bacteria resistant to antimicrobials and transfer of related genes is a complex issue and occurs, among other pathways, via meat consumption. In a context of limited resources, the prioritization of risk management activities is essential. Since the antimicrobial resistance (AMR) situation differs substantially between countries, prioritization should be country specific. The objective of this study was to develop a systematic and transparent framework to rank combinations of bacteria species resistant to selected antimicrobial classes found in meat, based on the risk they represent for public health in Switzerland. A risk assessment model from slaughter to consumption was developed following the Codex Alimentarius guidelines for risk analysis of foodborne AMR. Using data from the Swiss AMR monitoring program, 208 combinations of animal species/bacteria/antimicrobial classes were identified as relevant hazards. Exposure assessment and hazard characterization scores were developed and combined using multicriteria decision analysis. The effect of changing weights of scores was explored with sensitivity analysis. Attributing equal weights to each score, poultry-associated combinations represented the highest risk. In particular, contamination with extended-spectrum β-lactamase/plasmidic AmpC-producing Escherichia coli in poultry meat ranked high for both exposure and hazard characterization. Tetracycline- or macrolide-resistant Enterococcus spp., as well as fluoroquinolone- or macrolide-resistant Campylobacter jejuni, ranked among combinations with the highest risk. This study provides a basis for prioritizing future activities to mitigate the risk associated with foodborne AMR in Switzerland. A user-friendly version of the model was provided to risk managers; it can easily be adjusted to the constantly evolving knowledge on AMR.

Antimicrobial consumption on Austrian dairy farms: an observational study of udder disease treatments based on veterinary medication records

Background

Antimicrobial use in livestock production is an important contemporary issue, which is of public interest worldwide. Antimicrobials are not freely available to Austrian farmers and can only be administered to livestock by veterinarians, or by farmers who are trained members of the Animal Health Service. Since 2015, veterinarians have been required by law to report antimicrobials dispensed to farmers for use in food-producing animals. The study presented here went further than the statutory framework, and collected data on antimicrobials dispensed to farmers and those administered by veterinarians.

Methods

Seventeen veterinary practices were enrolled in the study via convenience sampling. These veterinarians were asked to contact interested dairy farmers regarding participation in the study (respondent-driven sampling). Data were collected from veterinary practice software between 1st October 2015 and 30th September 2016. Electronic data (89.4%) were transferred via an online interface and paper records (10.6%) were entered by the authors. Antimicrobial treatments with respect to udder disease were analysed by number of defined daily doses per cow and year (nDDD_vet/cow/year), based on the European Medicines Agency technical unit, Defined Daily Dose for animals (DDD_vet). Descriptive statistics and the Wilcoxon rank sum test were used to analyse the results.

Results

Antimicrobial use data from a total of 248 dairy farms were collected during the study, 232 of these farms treated cows with antibiotics; dry cow therapy was excluded from the current analysis. The mean number of DDD_vet/cow/year for the antimicrobial treatment of all udder disease was 1.33 DDD_vet/cow/year. Of these treatments, 0.73 DDD_vet/cow/year were classed as highest priority critically important antimicrobials (HPCIAs), according to the World Health Organization (WHO) definition. The Wilcoxon rank sum test determined a statistically significant difference between the median number of DDD_vet/cow/year for acute and chronic mastitis treatment (W = 10,734, p < 0.001). The most commonly administered antimicrobial class for the treatment of acute mastitis was beta-lactams. Intramammary penicillin was used at a mean of 0.63 DDD_vet/cow/year, followed by the third generation cephalosporin, cefoperazone, (a HPCIA) at 0.60 DDD_vet/cow/year. Systemic antimicrobial treatments were used at a lower overall level than intramammary treatments for acute mastitis.

Discussion

This study demonstrated that Austrian dairy cows in the study population were treated with antimicrobial substances for udder diseases at a relatively low frequency, however, a substantial proportion of these treatments were with substances considered critically important for human health. While it is vital that sick cows are treated, reductions in the overall use of antimicrobials, and critically important substances in particular, are still possible.

Comparison of treatment records and inventory of empty drug containers to quantify antimicrobial usage in dairy herds

Assessment of antimicrobial use (AMU) is vital for interpreting the origin of changes in antimicrobial resistance (AMR). The objectives of the present study were to estimate the association between AMU determined using on-farm treatment records (TR) and inventory of empty drug containers (INV). Herds were selected to represent Canadian dairy farms. Producers were asked to record animal health events and treatments on a standard General Health Event form. For inventory data, 40-L receptacles were placed at various locations considered convenient to deposit all empty drug containers. Antimicrobial defined-daily dosages (ADD) were calculated for 51 Canadian herds using the 2 methods. Estimation of AMU was 31,840 ADD using the INV and 14,487 ADD using the TR, indicating that for every TR entry, 2.20 times more treatments were observed using the INV. Mastitis, reproductive conditions, and dry cow therapy were the most frequent reasons for antimicrobial therapy when assessing TR. For all antimicrobials evaluated, mean ADD was higher using the INV versus TR. Regardless, a strong positive correlation (0.80) was observed between the 2 methods, indicating that herds with increased number of ADD recorded using the INV also had increased number of ADD recorded using TR. Furthermore, a positive association was observed for the 6 most commonly used antimicrobials. In comparison to methods used in surveillance programs on AMU in livestock that assume a constant use in all herds (i.e., sales data), INV provided a herd-level specific quantity of AMU positively correlated with AMU recorded at the animal level in general. The INV was easy to implement and provided a measure of total AMU in the herd. Availability of such information would be valuable for interpreting changes in AMR at the herd level and enabling evaluation of interventions for decreasing AMR.