Antimicrobial drug use in Austrian pig farms: plausibility check of electronic on-farm records and estimation of consumption

Longitudinal metagenomic study reveals the dynamics of fecal antibiotic resistome in pigs throughout the lifetime

BACKGROUND

The dissemination of antibiotic resistance genes (ARGs) poses a substantial threat to environmental safety and human health. Herein, we present a longitudinal paired study across the swine lifetime from birth to market, coupled with metagenomic sequencing to explore the dynamics of ARGs and their health risk in the swine fecal microbiome.

RESULTS

We systematically characterized the composition and distribution of ARGs among the different growth stages. In total, 829 ARG subtypes belonging to 21 different ARG types were detected, in which tetracycline, aminoglycoside, and MLS were the most abundant types. Indeed, 134 core ARG subtypes were shared in all stages and displayed a growth stage-associated pattern. Furthermore, the correlation between ARGs, gut microbiota and mobile genetic elements (MGEs) revealed Escherichia coli represented the main carrier of ARGs. We also found that in most cases, the dominant ARGs could be transmitted to progeny piglets, suggesting the potential ARGs generation transmission. Finally, the evaluation of the antibiotic resistance threats provides us some early warning of those high health risk ARGs.

CONCLUSIONS

Collectively, this relatively more comprehensive study provides a primary overview of ARG profile in swine microbiome across the lifetime and highlights the health risk and the intergenerational spread of ARGs in pig farm.

Use of Antimicrobials by Class in Pigs in Germany-A Longitudinal Description Considering Different International Categorisation Systems

Antimicrobial usage in both human and veterinary medicine is considered one of the main drivers of antimicrobial resistance; its reduction poses a serious challenge. To analyse the associations between usage and resistance, data from monitoring systems and classification of all antimicrobial substances are crucial. In this analysis, we investigated longitudinal data collected between 2013 and 2020 within the Veterinary Consumption of Antibiotics project from pig farms in Germany, including all antimicrobial classes, but focusing on critically important antimicrobials: third- and fourth-generation cephalosporins, fluoroquinolones, macrolides, and polymyxins. Analysing the treatment frequency, we found that a reduction in antimicrobial use in all types of pig production has occurred over time, accompanied by a rising percentage of farms without any usage. The lists of the World Health Organisation, World Organisation for Animal Health, and European Medicine Agency classify different antimicrobial substances as critically important. The vast differences between the respective weighted treatment frequencies allocated to the antimicrobials of main interest reflect the huge impact of the three categorisation systems. We concluded that, with the aim of creating national treatment guidelines supporting veterinarians to make treatment decisions, the list of the European Medicine Agency is the most suitable.

Assessing Knowledge, Beliefs, and Behaviors around Antibiotic Usage and Antibiotic Resistance among UK Veterinary Students: A Multi-Site, Cross-Sectional Survey

Antimicrobial resistance (AMR) is a profound threat to human and animal health. Antimicrobial prescribing behaviours are influenced by psychological factors such as knowledge, beliefs, and emotions. As future antimicrobial prescribers, it is important to understand beliefs about AMR and stewardship among veterinary (vet) students. This cross-sectional online survey assessed vet students’ self-reported behavior, knowledge, and beliefs in specific relation to antibiotic resistance (ABR) and antibiotic usage. Participants were early years (first- and second-year; n = 460) and later-years (third- and fourth-year; n = 113) undergraduate vet students from three UK universities. Self-reported antibiotic-related behaviors were responsible among most students. Knowledge about ABR and stewardship was moderate among early years students and good among later years students. Vet students typically believed that vets had less responsibility for both causing and preventing ABR than other groups (animal owners, human medics, and the public). This study offers evidence that vet students (along with other groups) tend to lay greater responsibility for ABR/AMR outside of their own profession, which may impact their future prescribing behaviors. It is vital that AMR and antimicrobial stewardship are embedded across veterinary curricula, and that the One Health nature of the challenge posed by AMR is emphasized to encourage shared responsibility across all stakeholder groups, thereby helping to reduce ‘other-blaming’ for AMR.

Survey on storage, application and incorporation practices for organic fertilizers in Germany

Organic fertilizers from animal production might contain undesirable components, such as veterinary medical product (VMP) residues, that are released into the environment during application. In addition to measures to reduce the use of VMPs through animal health measures, manure management could be an expedient strategy to prevent VMPs from entering the environment. The quantity applied is mainly determined by the nitrogen content. In addition, the depth of incorporation into the soil plays a major role in the environmental risk assessment of VMPs. The new regulations of the German fertilizer ordinance (DüV, 2020), which came into force at the beginning of 2020, as well as the changes that have not yet been fully implemented, will result in adjustments to the storage, application and incorporation practices for organic fertilizer. The aim of this study was to gain more information about the practice of storage, application and incorporation and the challenges for farmers in Germany. An online survey among farmers was conducted to determine the status quo. Almost all of the 125 participants kept livestock, predominantly cattle (68%) and pigs (33%). A third of participants (30%) needed a temporary storage site, for example at neighboring farms. Of the participants, 81% (n = 125) owned cropland and/or grassland. On cropland, manure was mostly incorporated at a depth of 3-15 cm, whereas on grassland, it was mostly applied superficially. On grassland lower-emission application techniques such as slot drill or injector procedures have so far rarely been used. The survey results provided important insights about storage, application and incorporation practices for organic fertilizers in Germany which could be used for the calculation of predicted environmental concentrations (PEC) as part of the environmental risk assessments of veterinary pharmaceuticals.

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.

Current Update on Intrinsic and Acquired Colistin Resistance Mechanisms in Bacteria

Colistin regained global interest as a consequence of the rising prevalence of multidrug-resistant Gram-negative Enterobacteriaceae. In parallel, colistin-resistant bacteria emerged in response to the unregulated use of this antibiotic. However, some Gram-negative species are intrinsically resistant to colistin activity, such as Neisseria meningitides, Burkholderia species, and Proteus mirabilis. Most identified colistin resistance usually involves modulation of lipid A that decreases or removes early charge-based interaction with colistin through up-regulation of multistep capsular polysaccharide expression. The membrane modifications occur by the addition of cationic phosphoethanolamine (pEtN) or 4-amino-l-arabinose on lipid A that results in decrease in the negative charge on the bacterial surface. Therefore, electrostatic interaction between polycationic colistin and lipopolysaccharide (LPS) is halted. It has been reported that these modifications on the bacterial surface occur due to overexpression of chromosomally mediated two-component system genes (PmrAB and PhoPQ) and mutation in lipid A biosynthesis genes that result in loss of the ability to produce lipid A and consequently LPS chain, thereafter recently identified variants of plasmid-borne genes (mcr-1 to mcr-10). It was hypothesized that mcr genes derived from intrinsically resistant environmental bacteria that carried chromosomal pmrC gene, a part of the pmrCAB operon, code three proteins viz. pEtN response regulator PmrA, sensor kinase protein PmrAB, and phosphotransferase PmrC. These plasmid-borne mcr genes become a serious concern as they assist in the dissemination of colistin resistance to other pathogenic bacteria. This review presents the progress of multiple strategies of colistin resistance mechanisms in bacteria, mainly focusing on surface changes of the outer membrane LPS structure and other resistance genetic determinants. New handier and versatile methods have been discussed for rapid detection of colistin resistance determinants and the latest approaches to revert colistin resistance that include the use of new drugs, drug combinations and inhibitors. Indeed, more investigations are required to identify the exact role of different colistin resistance determinants that will aid in developing new less toxic and potent drugs to treat bacterial infections. Therefore, colistin resistance should be considered a severe medical issue requiring multisectoral research with proper surveillance and suitable monitoring systems to report the dissemination rate of these resistant genes.

Antimicrobial use on 74 Japanese pig farms in 2019: A comparison of Japanese and European defined daily doses in the field

Defined daily doses (DDD) have been established in human medicine to standardize the measurement of treatment in a population. In veterinary medicine, the European Medicine Agency published defined daily dose (DDDvet) values for antimicrobial agents used in food-producing animals in 2016. National defined doses (DDDjp) for antimicrobials used for pigs in Japan have recently been determined. The aim of this study was to compare the results of calculated antimicrobial use in the field using the DDDjp and DDDvet values. Data from 74 pig farms in Japan relative to antimicrobial use in 2019 was collected. The numbers of DDDs (the weight of biomass treated in kg-days) using DDDjp and DDDvet values for each farm and for different antimicrobial classes were compared. Associations between calculated numbers of DDDjp and DDDvet on farm level were investigated. In addition, differences in antimicrobial use were investigated between different production types of farms (farrowing, finishing and farrow-to-finish farms). Using DDDjp and DDDvet values, the aggregated number of DDDs for 74 farms were 4,099,188 and 2,217,085 respectively, with the former being larger by 1.85 times than the latter. The most frequently used antimicrobial class was penicillin regardless of whether DDDjp or DDDvet was used. The absence of DDDvet values for certain antimicrobial agents used in Japan and the differences in the number of DDDjps/PCU and DDDvets/PCU indicated the need for Japanese DDDs. The number of DDDs per kg population correction unit (PCU) per farm tended to be higher in farrowing farms than in farrow-to-finish farms and finishing farms, with no significant difference (P = 0.19).

High Heritabilities for Antibiotic Usage Show Potential to Breed for Disease Resistance in Finishing Pigs

The use of antimicrobials in animal production is under public debate, mainly due to the risk of transfer of resistance to pathogenic bacteria in humans. Therefore, measures have been taken during the last few decades to reduce antibiotic usage in animals, for instance, by national monitoring programmes and by improving animal health management. Although some initiatives exist in molecular genetic selection, quantitative genetic selection of animals towards decreased antibiotic usage is an underexplored area to reduce antibiotic usage. However, this strategy could yield cumulative effects. In this study, we derived new phenotypes from on-farm parenteral antibiotic records from commercially grown crossbred finishing pigs used in the progeny test of Piétrain terminal sires to investigate the heritability of antibiotics usage. Parenteral antibiotic records, production parameters and pedigree records of 2238 full-sib pens from two experimental farms in Belgium between 2014 and 2020 were analysed. Heritability estimates were moderate (18–44%) for phenotypes derived from all antibiotic treatments, and low (1–15%) for phenotypes derived from treatments against respiratory diseases only. Moreover, genetic correlations between these new phenotypes and mortality were low to moderate (0.08–0.60) and no strong adverse genetic correlations with production traits were found. The high heritabilities and favourable genetic correlations suggest these new phenotypes, derived from on-farm antibiotics records, to be promising for inclusion in future pig breeding programs to breed for a decrease in antibiotics usage.

Examining the Effect of Context, Beliefs, and Values on UK Farm Veterinarians' Antimicrobial Prescribing: A Randomized Experimental Vignette and Cross-Sectional Survey

Antimicrobial resistance (AMR) is a pressing threat to public and animal health. There is evidence that antimicrobial prescribing and stewardship behaviors by veterinarians (vets) are influenced by non-clinical factors, such as psychological, social, and environmental factors. This study explored the role of context, beliefs, and values on vets' antimicrobial prescribing decisions. UK-based practicing farm vets (n = 97) were recruited to an online study. Using an experimental vignette methodology, vets were randomly assigned across four conditions, to examine the effects of different contexts (pressure on farm economics, the farmer, or the vet-farmer relationship, compared to a control condition) on vets' likelihood of prescribing antibiotics. Vets' beliefs about different groups' responsibility for causing and preventing AMR and vets' values were also measured. Key findings were that context alone, values, and beliefs about groups' responsibilities for causing AMR were not predictive of vets' likelihood of prescribing antibiotics. However, vets' beliefs about groups' responsibilities for preventing AMR were predictive of an increased likelihood of prescribing antibiotics, when vets were exposed to the experimental condition of the vignette in which the vet-farmer relationship was under pressure. Farm vets also believed that different groups have different levels of responsibility for causing and preventing AMR. Results should be interpreted cautiously, given the smaller than planned for sample size, and the possibility for both false negatives and false positives. Further research is needed to explore how these findings could inform antimicrobial stewardship interventions in veterinary medicine.

Estimating antimicrobial usage based on sales to beef and dairy farms from UK veterinary practices

BACKGROUND

Accurate estimation of antimicrobial use (AMU) is important in assessing reduction of agricultural AMU. This cross-sectional study aimed to evaluate several approaches for estimating AMU at the herd level and to report on AMU for beef and dairy farms in Scotland.

METHODS

Pharmaceutical sales data for 75 cattle herds (2011-2015) were screened for antimicrobial products and aggregated by herd and year. Several denominators for usage estimates were calculated and compared for their suitability at the herd level.

RESULTS

The median total mass of active ingredient sold per kg of bovine livestock was 9.5 mg/kg for beef herds and 14.3 mg/kg for dairy herds. The 'highest priority critically important' antimicrobials (HPCIA) were by total mass of active ingredient, 10.6% of all sales; by total defined daily dose veterinary (DDDVet), 29.8% and by DCDvet, 20.0%. These are the first estimates of AMU for beef cattle in the UK, and for cattle of any kind in Scotland. Estimates of herd-level usage based on population correction unit (PCU) were sensitive to low values for PCU for specific herd-years due to their demographic composition.

CONCLUSION

Pharmaceutical sales data can provide useful estimates of AMU, but estimating usage per PCU is not appropriate for comparing groups of cattle with different demographic compositions or for setting herd-level targets. Total mass of active ingredient per kilogram of livestock is more stable and hence suitable than PCU-based methods for assessing AMU at the herd level.

The Use of Antimicrobials in Italian Heavy Pig Fattening Farms

Data on antimicrobial use (AMU) in heavy pig production (>150 kg) are limited. The aim of this study was to investigate the AMU in this production. Data from 2015 were collected for 143 fattening farms. The AMU was estimated through a treatment index per 100 days (TI₁₀₀) using the defined daily dose animal for Italy (DDDAit). When possible, a comparison with the European Medicines Agency's defined daily doses for animals (DDDvet) was performed. The median TI₁₀₀ was 10.7 (range, 0.2-49.5). Group treatments represented 94.6% of overall consumption. The AMU calculated using DDDAit and DDDvet were strongly correlated (ρ = 0.976; p < 0.001). The AMU was negatively correlated with injectables use (ρ = -0.46, p < 0.001) and positively correlated with oral products (ρ = 0.21, p = 0.014), premixes (ρ = 0.26, p = 0.002), and mortality (ρ = 0.18; p = 0.027). Farm size was negatively correlated with AMU (ρ = -0.29, p < 0.001). Smaller farms were more frequently above the median TI₁₀₀ (odds ratio = 2.3, 95% confidence interval = 1.2-4.7), suggesting that they may have lower biosecurity and management standards. The results of this study should provide useful insights for the development of an Italian monitoring system.

Effect of antimicrobial use and production system on Campylobacter spp., Staphylococcus spp. and Salmonella spp. resistance in Spanish swine: A cross-sectional study

Antimicrobial resistance is a worldwide public health threat; hence, current trends tend to reduce antimicrobial use in food-producing animals and to monitor resistance in primary production. This study aimed at evaluating the impact of antimicrobial use and production system on swine farms in the antimicrobial resistance of Campylobacter, Salmonella and Staphylococcus, the main zoonotic pathogens in pig herds, in order to assess their potential value as sentinel microorganisms in antimicrobial resistance surveillance schemes. A total of 37 Spanish swine farms, 18 intensive and 19 organic/extensive farms, were included in the study. The antimicrobial resistance of 104 Campylobacter, 84 Staphylococcus and 17 Salmonella isolates was evaluated using Sensititre plates following the EUCAST guidelines. Mixed-effects logistic regression was used to evaluate the influence of production system and antimicrobial use in resistant and multidrug-resistant (MDR) phenotypes to the antimicrobials tested. The results showed that antimicrobial use was higher (p < .001) on intensive farms than on organic/extensive farms. MDR in Campylobacter and Staphylococcus was lower on organic/extensive farms (OR < .01p < .001). Antimicrobial resistance in Campylobacter and Staphylococcus isolates was, also for most of the antimicrobials studied, significantly higher in intensive than organic/extensive pig herds. Tetracycline resistance was associated with total antimicrobial consumption in both microbial species (p < .05), and some cross-associations between distinct antimicrobial substances were established, for instance resistance to erythromycin was associated with macrolide and phenicol consumption. No significant associations could be established for Salmonella isolates. The results demonstrate the link between antimicrobial consumption and resistance in zoonotic bacteria and evidence the potential value of using Campylobacter and Staphylococcus species in monitoring activities aimed at determining the impact of antimicrobials use/reduction on the occurrence and spread of antimicrobial resistance.

Colistin Update on Its Mechanism of Action and Resistance, Present and Future Challenges

Colistin has been extensively used since the middle of the last century in animals, particularly in swine, for the control of enteric infections. Colistin is presently considered the last line of defense against human infections caused by multidrug-resistant Gram-negative organisms such as carbapenemase-producer Enterobacterales, Acinetobacter baumanni, and Pseudomonas aeruginosa. Transferable bacterial resistance like mcr-genes was reported in isolates from both humans and animals. Researchers actively seek strategies to reduce colistin resistance. The definition of guidelines for colistin therapy in veterinary and human medicine is thus crucial. The ban of colistin use in swine as a growth promoter and for prophylactic purposes, and the implementation of sustainable measures in farm animals for the prevention of infections, would help to avoid resistance and should be encouraged. Colistin resistance in the human-animal-environment interface stresses the relevance of the One Health approach to achieve its effective control. Such measures should be addressed in a cooperative way, with efforts from multiple disciplines and with consensus among doctors, veterinary surgeons, and environment professionals. A revision of the mechanism of colistin action, resistance, animal and human use, as well as colistin susceptibility evaluation is debated here.

Quantification, description and international comparison of antimicrobial use on Irish pig farms

Background

There is concern that the use of antimicrobials in livestock production has a role in the emergence and dissemination of antimicrobial resistance in animals and humans. Consequently, there are increasing efforts to reduce antimicrobial use (AMU) in agriculture. As the largest consumer of veterinary antimicrobials in several countries, the pig sector is a particular focus of these efforts. Data on AMU in pig production in Ireland are lacking. This study aimed to quantify AMU on Irish pig farms, to identify the major patterns of use employed and to compare the results obtained to those from other published reports and studies.

Results

Antimicrobial use data for 2016 was collected from 67 Irish pig farms which represented c. 35% of national production. The combined sample population consumed 14.5 t of antimicrobial by weight of active ingredient suggesting that the pig sector accounted for approximately 40% of veterinary AMU in Ireland in 2016. At farm level, median AMU measured in milligram per population correction unit (mg/PCU) was 93.9 (range: 1.0–1196.0). When measured in terms of treatment incidence (TI200), median AMU was 15.4 (range: 0.2–169.2). Oral treatments accounted for 97.5% of all AMU by weight of active ingredient and were primarily administered via medicated feed to pigs in the post weaning stages of production. AMU in Irish pig production in 2016 was higher than results obtained from the national reports of Sweden, Denmark, the Netherlands and France but lower than the United Kingdom.

Conclusions

Pig production in Ireland is an important consumer of veterinary antimicrobials. The quantities and patterns of AMU on Irish pig farms are comparable to pig production in other European countries but higher than some countries with more advanced AMU reduction strategies. This AMU is characterised by a high proportion of prophylactic use and is primarily administered to pigs post weaning via medicated feed. Further studies to better understand the reasons for AMU on Irish pig farms and strategies to improve health among weaner pigs will be of benefit in the effort to reduce AMU.

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.

mcr-Colistin Resistance Genes Mobilized by IncX4, IncHI2, and IncI2 Plasmids in Escherichia coli of Pigs and White Stork in Spain

Colistin has become the last-line antimicrobial for the treatment of multidrug resistant (MDR) Enterobacterales in human medicine. To date, several colistin resistance genes have been described. Of them mcr-1 is disseminated worldwide in Escherichia coli of human and animal origin. The aim of this study was to characterize mcr-mediated resistance plasmids from E. coli of animal origin in Spain. From our strain collection, 70 E. coli of pig origin collected between 2005 and 2014 (10 per year, except for years 2009–2010–2013) were randomly selected and screened for the presence of mcr-genes. Additionally, 20 E. coli isolated in 2011 from white storks (Ciconia ciconia) from the same urban household waste landfill associated colony were also included. Whole genome sequencing of mcr-positive isolates was carried out on a MiSeq (Illumina). Hybrid whole genome sequencing strategy combining nanopore and Illumina technologies were performed in a selection of isolates to close the genomes and plasmids and identify the presence of antimicrobial resistance genes. Minimum inhibitory concentration (MIC) was used to assess the susceptibility to colistin. Mating experiments were carried out to evaluate transferability of the mcr-genes. A total of 19 mcr-1 and one mcr-4 positive isolates were detected, 15 from pigs distributed during the study period, and five from storks collected in 2011. No other mcr-variants were found. The MICs for colistin ranged between 4 and >4 mg/L. High diversity of STs were detected among the mcr-1 positive E. coli isolates, with only ST-10 shared between pigs and white storks. Except for one isolate, all were genotypic and phenotypically MDR, and five of them also harbored cephalosporin resistance genes (bla_CTX–M–14, bla_SHV–12, and three bla_CMY–2). mcr-1 genes were mobilizable by conjugation, associated with IncX4, IncHI2, and IncI2 plasmids. In our study, mcr-1 genes have been circulating in pig farms since 2005 harbored by a variety of E. coli clones. Its persistence may be driven by co-selection since plasmids containing mcr-1 also exhibit resistance to multiple drugs used in veterinary medicine. Furthermore, this is the first report of the presence of mcr-1 gene in isolates from white storks in Spain. This finding highlights the potential importance of wildlife that forage at urban household waste landfills in the transmission and spread of colistin resistance genes.

Colistin Resistance in Enterobacterales Strains - A Current View

Colistin is a member of cationic polypeptide antibiotics known as polymyxins. It is widely used in animal husbandry, plant cultivation, animal and human medicine and is increasingly used as one of the last available treatment options for patients with severe infections with carbapenem-resistant Gram-negative bacilli. Due to the increased use of colistin in treating infections caused by multidrug-resistant (MDR) bacteria, the resistance to this antibiotic ought to be monitored. Bacterial resistance to colistin may be encoded on transposable genetic elements (e.g. plasmids with the mcr genes). Thus far, nine variants of the mcr gene, mcr-1 – mcr-9, have been identified. Chromosomal resistance to colistin is associated with the modification of lipopolysaccharide (LPS). Various methods, from classical microbiology to molecular biology methods, are used to detect the colistin-resistant bacterial strains and to identify resistance mechanisms. The broth dilution method is recommended for susceptibility testing of bacteria to colistin.

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.

Antimicrobial usage on 72 farrow-to-finish pig farms in Japan from 2015 to 2017

In Japan veterinary antimicrobials are used most in the pig production sector. However, there is a paucity of data on the quantity of antimicrobials used on pig farms in Japan. This study describes antimicrobial use on Japanese pig farms in 2015, 2016 and 2017 in terms of mg of active ingredient per kg of PCU (population correction unit). Data on antimicrobial use from a total of 72 farrow-to finish farms over these three years were used in the study. The results revealed that the average use of antimicrobials in 2015, 2016 and 2017 was 304.8 (SD = 226.3), 311.2 (SD = 241.0) and 342.9 (SD = 291.3) mg/kg PCU, respectively. Most (97%) of the antimicrobials were administered orally. The most commonly used antimicrobials were tetracyclines, followed by macrolides, penicillins and sulfonamides. Tohoku was the region in which the lowest quantities of antimicrobial were used whilst South Kanto was the region in which the largest amount was used. The use of antimicrobials was on the increase in the North Kanto, South Kanto and Kyushu regions.

Antimicrobial Use on 36 Beef Feedlots in Western Canada: 2008-2012

The accurate quantification of antimicrobial use (AMU) in production animals is critical for monitoring trends in exposure to antimicrobial drugs (AMD) over time and examining potential associations with antimicrobial resistance in bacteria. In this study, a census sample of cattle was used to quantify individually-dosed and in-feed AMU as both numbers of animal daily doses (nADD) and total grams of AMD (gAMD) used in cattle placed in 36 western Canadian feedlots between 1-November, 2008 and 31-October, 2012; representing about 21.5% of fed cattle in Canada during that time period. Of the ~2.6 million cattle placed during the 48-month period, 45% were calves, 63% were male, 62% arrived in the fall or winter, and 39% were assessed as high risk for developing bovine respiratory disease (BRD). The proportion of cattle categorized as high risk (HR) for developing BRD was consistent over the 4 years of placement cohorts. Both medically important AMU and ionophore use were summarized but presented separately. A decrease in AMU was observed over the study period, both as nADD and total gAMD, which was primarily driven by a decline in the in-feed administration of tetracyclines. Most in-feed AMU was directed toward prevention and control of liver abscesses. The majority of individually dosed AMU was administered as metaphylaxis to address BRD risks, with category III AMD (medium importance to human medicine as categorized by Health Canada Veterinary Drugs Directorate) used most frequently. Not surprisingly, risk level for developing BRD influenced parenteral AMD exposures, with 95% of cattle categorized as being HR for developing BRD receiving individually dosed AMD compared to 59% of cattle categorized as being low risk (LR) for developing BRD. Cattle categorized as HR for developing BRD were more likely to receive macrolides for BRD metaphylaxis compared to cattle categorized as LR for developing BRD, and cattle categorized as LR for developing BRD were more likely to receive tetracycline for the same purpose. In summary, these data provide an unprecedented representation of AMU in fed cattle in western Canada and direction for future monitoring of AMU in fed cattle.

Used Daily Dose vs. Defined Daily Dose-Contrasting Two Different Methods to Measure Antibiotic Consumption at the Farm Level

Tackling the problem of rising antibiotic resistance requires valid and comparable data on the use of antimicrobial drugs in livestock. To date, no harmonized monitoring of antimicrobial usage in animals is available, and there is no system to assess usage data throughout Europe, thus hampering a direct comparison between different European countries. Most of the currently applied monitoring systems are based on sales data. Placement of sales data in relation to the population at risk requires overall assumptions about the weights of the animals treated and the doses applied. Only a few monitoring systems collect data in which the number of treated animals is reported exactly and does not need to be estimated. To evaluate the influence of different calculation methods on the standardizing procedure of antibiotic usage and benchmarking of farms, the treatment frequency for several farms (broiler, suckling piglets, and fattening pigs) was calculated in the following two different ways: first, based on the Used Daily Dose (TF_UDD), and second, based on the Defined Daily Dose (TF_DDD). To support this evaluation, consumption data from the Veterinary Consumption of Antibiotics Sentinel (VetCAb-S) project in Germany were used as example data. The results show discrepancies between both outcomes depending on the calculation method applied. In broiler holdings, the median values of TF_DDD were 20.89% lower than the median values of TF_UDD. In suckling piglets and fattening pig holdings, the median values of TF_DDD were increased 77.14% and 16.33%, respectively, which may have serious implications for the benchmarking of farms. Furthermore, this finding reflects that the calculation procedure also has an impact on the comparison between populations. Therefore, UDD-based calculations should be preferred to run monitoring systems with a benchmark mission. If, in contrast, the DDD approach is chosen to compare antimicrobial usage between populations, additional considerations should be made to adjust for the addressed discrepancies.

Patterns of antibiotic use in global pig production: A systematic review

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Many classes of antibiotic used for humans are also used in food animals, including the highest priority of the critically important antimicrobials for human medicine in the World Health Organisation's list.

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Penicillins and Tetracyclines classes were the most commonly used antibiotics in many countries.

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Improve understanding of the use of antibiotics and factors influencing antibiotic use will help promoting prudent use of antimicrobials in livestock.

This review assesses the evidence for patterns of antibiotic use in pig on the basis of papers published in peer-reviewed journals in English between 2000 and 2017. Thirty-six articles were identified and reviewed, of which more than 85% of studies were conducted in Europe and North America. Penicillins and Tetracyclines groups were the most commonly used antibiotics in many countries. Oral medication in suckling and post-weaning periods were the most common applications of antibiotic administration in pig production. Antibiotic use is driven by age-specific diseases and the common pathogens causing these conditions where epidemiological profiles varied greatly across countries. In addition, the type and size of farm were associated with antibiotic use with finisher and larger farms using more antibiotics than farrow-to-finish and smaller farms. There is variation in the use of the highest priority critically important antimicrobials in humans across studies. However, this review indicates that they are still commonly used in pig production, for treatment and prevention of infection. This evidence calls for global efforts on the prudent use of antibiotics in response to the emergence of antimicrobial resistance (AMR) in the agricultural sector.

The use of antimicrobials in global pig production: A systematic review of methods for quantification

BACKGROUND

Overuse of antimicrobials in both humans and animals is recognized as one of the main drivers of Antimicrobial Resistance (AMR); and the optimisation of their use has been advocated as a key strategy for dealing with AMR. The measurement of antimicrobial use is vital for the design, monitoring and evaluation of such strategies. This systematic review describes and compares methods and measurements used to quantify antimicrobial use in pigs in order to inform efforts to standardize measurement.

METHODS

The peer-reviewed literature was systematically searched using four online databases: MEDLINE, ScienceDirect, Scopus and Web of Science. Eligibility criteria for inclusion in the review included: articles published in English, involving pigs of any age and types of production, providing quantitative data on antimicrobial use, containing a clear description of the methodology, and having moderate to high rank in the quality assessment.

RESULTS

Of 2,362 abstracts reviewed, a total of 25 studies were included based on the eligibility criteria. All studies were published between 2001 and 2017. Twenty of the studies were conducted in eight European countries. Twelve studies estimated antimicrobial use and eight studies were primarily methodological papers comparing different methods or variables, or developing new methods. The two main sources of antimicrobial use data were farm surveys and national sales data. A large variety of units of measurement was found. In this review, the ten measurements identified were categorized into four groups: 1) antimicrobials use measured by milligrams of active substance per animal weight; 2) antimicrobials use measured by daily dose per weight at treatment; 3) antimicrobial use measured by daily dose per treatment period; and 4) antimicrobials use measured by daily dose per period at risk of treatment.

CONCLUSION

There is no global standardized measurement of antimicrobial use in pigs. Given the importance of monitoring the use antimicrobials, we recommend that at a minimum, all countries should develop macro-level monitoring using national sales data and report use by milligram of active ingredients per Population Correcting Unit. Monitoring in specific animal species requires the development of systems to capture prescription at national or farm level. Findings from monitoring antimicrobial use may help to guide effective interventions for optimising use of antimicrobials, as recommended by the WHO Global Action Plan on AMR.

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.

Antibiotic use on German pig farms - A longitudinal analysis for 2011, 2013 and 2014

To study antibiotic use in livestock in a temporal context with the development of antimicrobial resistance, long-term changes in antibiotic use must be mapped and their possible causes must be explored. Therefore, the present work assesses the changes in antibiotic use over time in German livestock husbandry. In addition, factors associated with antibiotic use were analyzed to identify possible strategies for further reducing antimicrobial usage. For 2011, 2013 and 2014, antibiotic usage data were collected and examined within the VetCAb project. Three hundred participating pig holdings provided information on their antibiotic use based on obligatory application and delivery forms (ADFs) filled in by their veterinarian as well as information on their current stabling capacities for each production type held. Data on sow, piglet, weaner and fattening pig holdings were described separately, using the semi-annual treatment frequency (TF) to measure antibiotic consumption. Multiple linear mixed models were used to investigate the effects of time, farm size, region and farm management category on the treatment frequency. The study yielded significant time changes with p-values below 0.001 in antibiotic administration with a decreasing median TF in piglets from 3.8 in the first half of 2011 (IQR = 1.1-10.6) to 1.7 in the second half of 2014 (IQR = 0.2-4.5) and in fattening pigs from 5.1 in the first half of 2011 (IQR = 0.2-15.4) to 0.7 in the second half of 2014 (IQR = 0.1-6.7). Meanwhile the TF fluctuated between 8.2 and 12.2 in weaners during the observational period (IQRs between zero (lower quartile) and 37.9 (upper quartile)). Piglet, weaner and fattening pig holdings belonging to the upper third of the holdings in size used significantly more antibiotics than the other holdings investigated. Particularly for weaner and fattening pig holdings, a higher TF was noted for farms without breeding units. The region was only a significant factor in weaners. In conclusion, for 2011, 2013 and 2014, the present study shows a clear reduction in antibiotic treatment frequency in German pig holdings. In addition, the association with various factors such as herd size and farm organization on the antibiotic usage frequency is indisputable. Therefore, these factors should be included in monitoring systems and considered when evaluating intervention measures.

Effect of Early-Life Treatment of Piglets with Long-Acting Ceftiofur on Colonization of Streptococcus suis Serotype 7 and Elicitation of Specific Humoral Immunity in a Farm Dealing with Streptococcal Diseases

In newborn piglets treatment with long-acting ceftiofur is a common approach to reduce losses due to streptococcal diseases on farms, even if problems start after weaning. The purpose of this study was to examine the influence of a single early-life treatment on Streptococcus (S.) suis colonization, transmission, immunoreaction, and drug resistance over an observation period of 14 weeks. In a farm with a history of streptococcal disease and isolation of a S. suis cps 7 mrp+, arcA+ isolate from diseased piglets, half of each litter was treated with a long-acting ceftiofur on day 1. S. suis-isolates were profiled and serum samples were tested for opsonizing antibodies. Treated and untreated pigs did not differ according to average daily weight gains, S. suis-isolation rates and level of opsonizing antibodies. Although the invasive cps 7 strain was not detected in a single piglet over 14 weeks, all animals developed bactericidal activity. No resistance to ceftiofur, but resistance to tetracyclins (100%), and trimethoprim/sulfamethoxazole (53%) was shown. Our results indicate that early treatment with ceftiofur does not prevent colonization and transmission of S. suis or the induction of bactericidal humoral immunity in nursery and fattening pigs. The necessity of continuous usage should be reconsidered.

Control of Antimicrobial Resistance Requires an Ethical Approach

Ethical behavior encompasses actions that benefit both self and society. This means that tackling antimicrobial resistance (AMR) becomes an ethical obligation, because the prospect of declining anti-infectives affects everyone. Without preventive action, loss of drugs that have saved lives over the past century, will condemn ourselves, people we know, and people we don't know, to unacceptable risk of untreatable infection. Policies aimed at extending antimicrobial life should be considered within an ethical framework, in order to balance the choice, range, and quality of drugs against stewardship activities. Conserving availability and effectiveness for future use should not compromise today's patients. Practices such as antimicrobial prophylaxis for healthy people 'at risk' should receive full debate. There are additional ethical considerations for AMR involving veterinary care, agriculture, and relevant bio-industries. Restrictions for farmers potentially threaten the quality and quantity of food production with economic consequences. Antibiotics for companion animals do not necessarily spare those used for humans. While low-income countries cannot afford much-needed drugs, pharmaceutical companies are reluctant to develop novel agents for short-term return only. Public demand encourages over-the-counter, internet, black market, and counterfeit drugs, all of which compromise international control. Prescribers themselves require educational support to balance therapeutic choice against collateral damage to both body and environment. Predicted mortality due to AMR provides justification for international co-operation, commitment and investment to support surveillance and stewardship along with development of novel antimicrobial drugs. Ethical arguments for, and against, control of antimicrobial resistance strategies are presented and discussed in this review.

Antimicrobial use in food-producing animals: a rapid evidence assessment of stakeholder practices and beliefs

Food-producing animals throughout the world are likely to be exposed to antimicrobial (AM) treatment. The crossover in AM use between human and veterinary medicine raises concerns that antimicrobial resistance (AMR) may spread from food-producing animals to humans, driving the need for further understanding of how AMs are used in livestock practice as well as stakeholder beliefs relating to their use. A rapid evidence assessment (REA) was used to collate research on AM use published in peer-reviewed journals between 2000 and 2016. Forty-eight papers were identified and reviewed. The summary of findings highlights a number of issues regarding current knowledge of the use of AMs in food-producing animals and explores the attitudes of interested parties regarding the reduction of AM use in livestock. Variation between and within countries, production types and individual farms demonstrates the complexity of the challenge involved in monitoring and regulating AM use in animal agriculture. Many factors that could influence the prevalence of AMR in livestock are of concern across all sections of the livestock industry. This REA highlights the potential role of farmers and veterinarians and of other advisors, public pressure and legislation to influence change in the use of AMs in livestock.

Evaluation of antibiotic usage in swine reproduction farms in Umbria region based on the quantitative analysis of antimicrobial consumption

Antibiotic use in food-producing animals has considerable impact on public health, especially with respect to the development and spread of antibiotic resistance. Pigs represent one of the main species in which antibiotics are frequently used for different purposes. Surveillance of antibiotic consumption and dose appropriateness, through novel approaches based on defined daily doses, is strongly needed to assess farms' antibiotic risk, in terms of spread of antibiotic resistance and possibile presence of residues in meat. In this study, antibiotic consumption was monitored in 14 swine reproduction farms, together with managerial, structural, and health aspects. Most of the controlled farms (65%) were classified as at medium antibiotic risk, 21% at high antibiotic risk, and 14% at low antibiotic risk. Critical aspects of antibiotic administration concerned treatments for suckling and weaner piglets, oral antibiotic administration, treatment and diagnosis of gastroenteric infections, and use of critically important antimicrobials for human medicine, especially colistin. These aspects could be considered critical aspects of antibiotic use in from-farrow-to-wean/finish swine farms in the Umbria region and must be controlled to minimize risks. Even though a small number of farms in Umbria region are at high antibiotic risk, the risk of antibiotic resistance should be minimized, and management and biosecurity of the farms should be improved by extending the use of antimicrobial susceptibility tests and optimizing the diagnostic methods for infectious diseases. Furthermore, farmers' and veterinarians' knowledge of antibiotic resistance should be improved and the prudent use of antibiotics encouraged to prevent the development and spread of resistant microorganisms.

Colistin in Pig Production: Chemistry, Mechanism of Antibacterial Action, Microbial Resistance Emergence, and One Health Perspectives

Colistin (Polymyxin E) is one of the few cationic antimicrobial peptides commercialized in both human and veterinary medicine. For several years now, colistin has been considered the last line of defense against infections caused by multidrug-resistant Gram-negative such as Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Colistin has been extensively used orally since the 1960s in food animals and particularly in swine for the control of Enterobacteriaceae infections. However, with the recent discovery of plasmid-mediated colistin resistance encoded by the mcr-1 gene and the higher prevalence of samples harboring this gene in animal isolates compared to other origins, livestock has been singled out as the principal reservoir for colistin resistance amplification and spread. Co-localization of the mcr-1 gene and Extended-Spectrum-β-Lactamase genes on a unique plasmid has been also identified in many isolates from animal origin. The use of colistin in pigs as a growth promoter and for prophylaxis purposes should be banned, and the implantation of sustainable measures in pig farms for microbial infection prevention should be actively encouraged and financed. The scientific research should be encouraged in swine medicine to generate data helping to reduce the exacerbation of colistin resistance in pigs and in manure. The establishment of guidelines ensuring a judicious therapeutic use of colistin in pigs, in countries where this drug is approved, is of crucial importance. The implementation of a microbiological withdrawal period that could reduce the potential contamination of consumers with colistin resistant bacteria of porcine origin should be encouraged. Moreover, the management of colistin resistance at the human-pig-environment interface requires the urgent use of the One Health approach for effective control and prevention. This approach needs the collaborative effort of multiple disciplines and close cooperation between physicians, veterinarians, and other scientific health and environmental professionals. This review is an update on the chemistry of colistin, its applications and antibacterial mechanism of action, and on Enterobacteriaceae resistance to colistin in pigs. We also detail and discuss the One Health approach and propose guidelines for colistin resistance management.

Colistin use and colistin resistance in bacteria from animals

Colistin has been used in veterinary medicine for decades, mainly for the prevention and treatment of Enterobacteriaceae infections. However, data regarding colistin resistance in bacteria from animals and food of animal origin are relatively scarce, partly because there are methodological difficulties hampering the analysis of susceptibility to colistin. Most data regarding clinical isolates are related to enteropathogenic Escherichia coli and Salmonella. The resistance percentages are sometimes high for pathogenic strains, and the mcr-1 gene has been detected in pathogenic E. coli isolates from pigs, cattle and poultry in different countries. The prevalence of colistin resistance in Salmonella from healthy animals is usually low but depends on the proportion of intrinsically colistin-resistant serotypes. For indicator E. coli, the resistance levels are often very low, although higher levels have been observed in Asia. The mcr-1 gene has been detected in indicator E. coli from pigs, cattle, poultry and their products. Thus, there is an urgent need to re-assess the use of colistin in livestock throughout the world to ensure a global strategy for preserving this last-resort antimicrobial.

Resistance to colistin: what is the fate for this antibiotic in pig production?

Colistin, a cationic polypeptide antibiotic, has reappeared in human medicine as a last-line treatment option for multidrug-resistant Gram-negative bacteria (MDR-GNB). Colistin is widely used in veterinary medicine for the treatment of gastrointestinal infections caused by Enterobacteriaceae. GNB resistant to colistin owing to chromosomal mutations have already been reported both in human and veterinary medicine, however several recent studies have just identified a plasmid-mediated mcr-1 gene encoding for colistin resistance in Escherichia coli colistin resistance. The discovery of a non-chromosomal mechanism of colistin resistance in E. coli has led to strong reactions in the scientific community and to concern among physicians and veterinarians. Colistin use in food animals and particularly in pig production has been singled out as responsible for the emergence of colistin resistance. The present review will focus mainly on the possible link between colistin use in pigs and the spread of colistin resistance in Enterobacteriaceae. First we demonstrate a possible link between Enterobacteriaceae resistance emergence and oral colistin pharmacokinetics/pharmacodynamics and its administration modalities in pigs. We then discuss the potential impact of colistin use in pigs on public health with respect to resistance. We believe that colistin use in pig production should be re-evaluated and its dosing and usage optimised. Moreover, the search for competitive alternatives to using colistin with swine is of paramount importance to preserve the effectiveness of this antibiotic for the treatment of MDR-GNB infections in human medicine.

Influence of porcine circovirus type 2 vaccination on the level of antimicrobial consumption on 65 Austrian pig farms

The administration of antibiotics to farm animals is an important contemporary topic. Veterinarians, pig producers, politicians, retailers and consumers all have a vested interest in reducing antimicrobial use on farm, while ensuring adequate health and welfare of food-producing animals. Vaccination programmes may be used to reduce the overall level of clinical disease in a population, subsequently leading to a decline in antimicrobial use. In 2008, a vaccination programme against porcine circovirus type 2 (PCV-2) was initiated in Austria. In the retrospective observational study presented here, farm medication records (2008-2011) from 65 conventional pig farms were evaluated. As PCV-2 has been shown to lead to generalised immunosuppression, enabling secondary bacterial infections to occur, the authors hypothesised that PCV-2 vaccination would decrease antimicrobial consumption at farm level. Firstly, we focused on the annual antimicrobial consumption expressed as the number of administered animal daily doses per kg liveweight (nADDkg/kg/year). Secondly, a linear mixed effects model was applied to evaluate the influence of PCV-2 vaccination on the antimicrobial consumption at farm level. The interaction between farm type and PCV-2 vaccination was found to be a highly significant factor (P=0.0002) influencing antimicrobial use at farm level. The estimated impact of PCV-2 vaccination revealed a highly significant (P<0.001) decline in total antimicrobial drug use from 1.72 ADDkg/kg/year to 0.56 ADDkg/kg/year on finishing farms, whereas only a negligible decline was detectable on farrow-to-finish farms.

Antibiotic use in dairy herds in the Netherlands from 2005 to 2012

The aim of this study was to examine the variation in antibiotic use and the effects of external factors on trends in antibiotic use at the herd level by using the number of daily dosages as an indicator for antibiotic use. For this purpose, antibiotic use was analyzed in 94 dairy herds in the Netherlands from 2005 to 2012. The herds were divided into 3 groups of farmers: one group was guided in their antibiotic use from 2008 to 2010 as part of the project, whereas the other 2 groups were not actively guided. The farms were located in 10 of the 12 provinces and were clients of 32 of the 300 veterinary practices that treat cattle. Sales invoices from the veterinary practices provided the antibiotic and cost data for the participating farmers. The number of animal-defined daily dosages (ADDD) indicates the number of days per year that the average cow in a herd is given antibiotic treatment. The average ADDD for all farms from 2005 to 2012 was 5.86 (standard deviation=2.14); 68% of ADDD were used for udder health, 24% for clinical mastitis and 44% for dry-cow therapy. Variation in ADDD among herds decreased during the study period. The trend in ADDD can be described as having 3 phases: (1) a period of increasing use coinciding with little public concern about antibiotic use (2005-2007), (2) a period of growing awareness and stabilization of use (2007-2010), and (3) a period of decreasing use coinciding with increasing societal concerns (2010-2012). The greatest reduction in use was for drugs other than those used to treat the udder. Drug use for mastitis treatment fell considerably in the final year of the study period, whereas farmers were reluctant to reduce use for dry-cow therapy. Almost 40% of the herds were given less than 2.5 ADDD for dry-cow therapy, which is equivalent to 2.5 tubes per average cow in the herd, and 20% used more than 3 tubes per cow. Use of third- and fourth-generation cephalosporins and fluoroquinolones dropped from 18% of ADDD during 2005 to 2010 to 1% in 2012, with a shift toward penicillins and broad spectrum drugs. The ADDD was 22% lower in 2012 than 2007, the year of the highest usage. The decrease in ADDD over time varied between the 3 groups of farmers. During the second phase of the study, the guided group began to display a reduction in use, whereas the other groups only displayed a significant reduction in the third phase. The reduction in antibiotic use has resulted in lower veterinary costs per cow in recent years.