No Clear Effect of Initiating Vaccination against Common Endemic Infections on the Amounts of Prescribed Antimicrobials for Danish Weaner and Finishing Pigs during 2007-2013

A review of the predictors of antimicrobial use and resistance in European food animal production

Antimicrobial resistance (AMR) is a major threat to global health and a key One Health challenge linking humans, animals, and the environment. Livestock are a key target for moderation of antimicrobial use (AMU), which is a major driver of AMR in these species. While some studies have assessed AMU and AMR in individual production systems, the evidence regarding predictors of AMU and AMR in livestock is fragmented, with significant research gaps in identifying the predictors of AMU and AMR common across farming systems. This review summarizes existing knowledge to identify key practices and critical control points determining on-farm AMU/AMR determinants for pigs, layer and broiler hens, beef and dairy cattle, sheep, turkeys, and farmed salmon in Europe. The quality and quantity of evidence differed between livestock types, with sheep, beef cattle, laying hens, turkeys and salmon underrepresented. Interventions to mitigate both AMU and/or AMR highlighted in these studies included biosecurity and herd health plans. Organic production typically showed significantly lower AMU across species, but even in antibiotic-free systems, varying AMR levels were identified in livestock microflora. Although vaccination is frequently implemented as part of herd health plans, its effects on AMU/AMR remain unclear at farm level. Social and behavioral factors were identified as important influences on AMU. The study fills a conspicuous gap in the existing AMR and One Health literatures examining links between farm management practices and AMU and AMR in European livestock production.

Productivity parameters, antimicrobial consumption, and prevalence of enteric pathogens before and after intramuscular vaccination against Lawsonia intracellularis in naturally infected Danish weaner and finisher pig herds

In Danish pig production, gastro-intestinal diseases account for most of the antimicrobials (AM) used in growing pigs. Diarrhoea is most frequently caused by Lawsonia intracellularis (LI), Brachyspira pilosicoli (BP), E coli fimbria type F4 (F4) and E. coli fimbria type F18 (F18). With a new LI vaccine available from 2019, it was relevant to investigate the effect of this vaccine in a Danish field study including both weaner and finisher sites. The aim was to evaluate the efficacy of Porcilis® Lawsonia Vet. in naturally LI-infected pig herds by comparing of productivity parameters, AM consumption and dynamics of enteric pathogens over two 6-months periods before and after LI vaccination. Further, faecal sock samples were collected from each site before and after vaccination and analysed by qPCR for excretion levels of LI, BP, F18 and F4. In total, 28 weaner and 41 finisher sites were included in the study. Vaccination reduced Feed Conversion Ratio by 0.12 Feed Unit/kg (p = 0.029) and 0.08 Feed Unit/kg (p = 0.005) in weaners and finishers, respectively. Increased Average Daily Weight Gain of 45.6 gr./day (p < 0.001) was found in the finishers. Mortality risk fell by 8.8% in weaners (RR = 0.912; p < 0.001). AM prescriptions for oral group treatments were reduced by 38.8% active compound/kg pig produced (p = 0.005) or 33.3% Weighted Animal Daily Doses per 100 animals per day in finishers (p = 0.004). LI prevalence was reduced in weaners and finishers (both p < 0.001) and BP prevalence was reduced in finishers (p = 0.043). Mean excretion levels of LI and BP decreased at weaner sites (-1.32 and -1.02 log(10) copies/gr faeces, respectively; both p < 0.001) and at finisher sites (-1.04 and -1.16 log(10) copies/gr faeces, respectively; both p < 0.001). Prevalence and excretion levels of F18 and F4 were unaffected by LI vaccination. In conclusion, vaccination against LI using Porcilis® Lawsonia Vet. improved productivity parameters, cut AM consumption, and reduced prevalence and excretion levels of LI and BP in naturally LI-infected pig herds.

Characterisation of antimicrobial usage in Danish pigs in 2020

Introduction

Denmark is one of the world's largest exporters of pigs and pig meat, so the sector plays an important role in the national antimicrobial use (AMU). The Danish government has run antimicrobial stewardship programs in collaboration with the pig industry for more than 25 years. These have resulted in substantial overall reductions in total AMU and limiting the use of fluoroquinolones, the 3rd and 4th generation cephalosporines and the polymyxin colistin. To understand where further reductions in AMU could take place, it is necessary to investigate which antimicrobials are being used, how, and for which reasons.

Materials and methods

We characterized the AMU in the Danish pig sector in 2020, providing new analytical insights based on data retrieved from the VetStat database. The AMU data were segmented into classes, routes of administration, treatment indications and age groups, and interpreted as an outcome of the interventions taken. We evaluated the current AMU regarding choice of antimicrobial class. Moreover, we discussed how to further improve the antimicrobial stewardship in Danish pig production to achieve additional reductions without jeopardizing animal welfare. Where relevant, two pig veterinary specialists were consulted.

Results

In 2020, 43.3 mg antimicrobials per population correction unit (PCU) were ascribed to the Danish pig sector. There was practically no use of fluoroquinolones, 3rd and 4th generation cephalosporins and polymyxins. Weaners related to 45% of the total AMU in pigs when measured in tonnes and 81% when measured in defined animal daily doses, of these 76% were ascribed to gastrointestinal indications and overall, 83% were administered perorally.

Conclusion

To enable further reductions in AMU, it should be investigated how and when to replace group treatments (e.g., all animals in section or a pen) with individual treatments. Moreover, prevention of disease and promotion of animal health should be prioritized, e.g., through focus on feed, vaccination, biosecurity, and disease eradication.

Risk Factors for Antimicrobial Use on Irish Pig Farms

Simple Summary

Antimicrobial resistance (AMR) is a major threat to public health. There are concerns that antimicrobial use (AMU) in agriculture has a role in the development of AMR. Pigs are one of the main consumers of veterinary antimicrobials and a better understanding of the drivers for AMU in this sector will help in efforts to reduce use. The aim of this study was to investigate the associations between antimicrobial use, farm characteristics, biosecurity, the presence of respiratory disease on the farm and health management practices on Irish pig farms. Farms that manufactured their feed on-site had lower total AMU than farms that purchased their feed from a feed mill. Higher levels of lung abscesses and pericarditis (inflammation of the lining around the heart), both indicators of respiratory disease, were associated with increased AMU. Higher levels of pericarditis were also associated with increased use of critically important antimicrobials. Farms vaccinating against swine influenza also had higher AMU. Farms that administered prophylactic antimicrobial treatments to piglets had higher use of individual treatments and critically important antimicrobials. The results from this study show that prophylaxis and respiratory disease are the main drivers of AMU on Irish pig farms. These findings highlight areas of farm management where interventions may aid in reducing AMU on Irish pig farms.

Abstract

The threat to public health posed by antimicrobial resistance in livestock production means that the pig sector is a particular focus for efforts to reduce antimicrobial use (AMU). This study sought to investigate the risk factors for AMU in Irish pig production. Antimicrobial use data were collected from 52 farrow-to-finish farms. The risk factors investigated were farm characteristics and performance, biosecurity practices, prevalence of pluck lesions at slaughter and serological status for four common respiratory pathogens and vaccination and prophylactic AMU practices. Linear regression models were used for quantitative AMU analysis and risk factors for specific AMU practices were investigated using logistic regression. Farms that milled their own feed had lower total AMU (p < 0.001), whereas higher finisher mortality (p = 0.043) and vaccinating for swine influenza (p < 0.001) increased AMU. Farms with higher prevalence of pericarditis (p = 0.037) and lung abscesses (p = 0.046) used more group treatments. Farms with higher prevalence of liver milk spot lesions (p = 0.018) and farms practising prophylactic AMU in piglets (p = 0.03) had higher numbers of individual treatments. Farms practising prophylactic AMU in piglets (p = 0.002) or sows (p = 0.062) had higher use of cephalosporins and fluoroquinolones. This study identified prophylactic use and respiratory disease as the main drivers for AMU in Irish pig production. These findings highlight areas of farm management where interventions may aid in reducing AMU on Irish pig farms.

Indications for the use of highest priority critically important antimicrobials in the veterinary sector

BACKGROUND

Among the measures taken to preserve the clinical efficacy of highest priority critically important antimicrobials (HP-CIAs), the WHO has recommended avoiding their use in food-producing animals. Little is known regarding the indications for which different antimicrobial classes are used in animals, even in countries where data on antimicrobial use are available.

OBJECTIVES

To outline, in a narrative review, the diseases for which HP-CIAs are used in veterinary medicine, highlighting incongruences with international guidelines and disease conditions where effective alternatives to HP-CIAs are missing.

METHODS

Scientific literature, national reports and expert opinion were used to describe the indications for the use of HP-CIAs in the main food-producing (pigs, cattle and poultry) and companion (horses, dogs and cats) animal species.

RESULTS

The most common indications for use of HP-CIAs are enteric and respiratory infections in pigs, cattle and poultry, urogenital infections in dogs and cats and respiratory infections in horses. In some instances, no valid and convenient alternatives to colistin and macrolides are available against certain porcine enteric and bovine respiratory pathogens. Effective, legal and convenient alternatives to HP-CIAs are also lacking for managing common infections in cats, for which oral administration is difficult, Rhodococcus equi infections in horses, some enteric and respiratory infections in poultry and MDR infections in all companion animal species.

CONCLUSIONS

Future research and stewardship programmes should focus on the disease conditions identified by this review to reduce the use of HP-CIAs in the veterinary sector.

Probiotics mediated gut microbiota diversity shifts are associated with reduction in histopathology and shedding of Lawsonia intracellularis

BACKGROUND

Clinical intervention during bacterial infections in farm animals such as pigs commonly includes the use of antimicrobials. With the rise of antimicrobial resistance and the attempts to reduce the use of antibiotics in food animals, effective alternatives are urgently needed to reduce or even remove pathogens and disease risks. Improving clinical outcomes and overall pig health by using probiotics appears attractive. However, reliable data sets on the efficacy of probiotics are scarce. The obligate intracellular bacterium Lawsonia intracellularis is widespread in pigs and associated with severe enteropathy, mainly in the ileum, commonly resulting in substantial reduction in weight gain. The impact of three in-feed probiotics and a commercial live L. intracellularis vaccine was compared in a pig challenge model. Probiotic treatment was associated with reduced L. intracellularis fecal shedding and reduced gut lesions. Here, the bacterial microbiota of the ileum of these pigs was characterized with 16S rRNA gene sequencing and was subsequently analyzed with bioinformatics tools.

RESULTS

The greatest microbial richness was observed in the probiotic treated group T03-LAW, which accounted for 87% of richness observed in the study. Treatment had a significant impact on both the microbiota structure and taxonomic profile in the ileum, explaining between 26 and 36% of the structural variation, with the strongest association in the T03-LAW group. Overall, the largest changes were observed for the pigs treated with in-feed Bacillus pumilus; the microbiota of these pigs had the greatest diversity and highest richness. We also observed depleted and enriched core microbiota amongst the groups; however, there was no correlation with clinical characteristics. The results suggest that an increased diversity of the ileal microbiota is associated with a reduction in shedding, i.e. a unit increase in Shannon diversity index resulted in 2.8 log reduction in shedding.

CONCLUSIONS

Probiotic supplementation of a base feed ration increased ileum microbiota diversity leading to a mitigation of the effects of a pathogenic L. intracellularis challenge. An even and diverse microbiota community benefits pigs infected with L. intracellularis, however, investigations are needed to determine if this is also true for other pathogens. The study unambiguously demonstrates the usefulness of probiotic supplementation in reducing the impact of enteric pathogens and pathogen shedding rates in food animals without the use of antimicrobials.

Antimicrobial Usage Among Different Age Categories and Herd Sizes in Swiss Farrow-to-Finish Farms

In the Swiss pig sector, the usage of antimicrobials has been recorded, evaluated and systematically reduced on a voluntary basis since 2015. This monitoring has been carried out using various methods thereby enabling continuous national scrutiny as well as international comparisons. To gain a better understanding of the dynamics of the antimicrobial usage on Swiss farms, consumption data of farrow-to-finish farms were analyzed for (i) the within-herd relationships among different age categories and (ii) the influence of the herd size. The data were collected on 71 farms for the year 2017, encompassing the amount of active ingredients and number of defined daily doses Switzerland (nDDDch) in total, and stratified for the different age categories of piglets, weaners, fattening pigs, and sows. The differences in nDDDch per animal among the age categories were determined by a Wilcoxon test and subsequent post-hoc analysis according to Bonferroni. The within-herd relationship among the individual age categories as well as the influence of the herd size on nDDDch per animal measured as kept sows were analyzed by simple linear regression. The evaluation of the treatment days showed that 50% of the nDDDch were used in piglets, 44% for weaners, and 3% each for fattening pigs and sows. Compared to the other age categories, the examination of the number of nDDDch per animal showed a significantly higher number for sows, whereas for fattening pigs the number was significantly lower (P < 0.01). The farm-based analysis using linear regression showed a relationship between antimicrobial usage in sows and piglets (P < 0.001; adj. R² = 0.19). Similarly, a significant relationship between larger herd size and increased antimicrobial usage was observed (P = 0.02; adj. R² = 0.06). The present study provides an insight into the antimicrobial treatment dynamics of farrow-to-finish farms. In particular, the age categories piglets and sows—with their higher number of treatment days in total or per animal—are of interest regarding the potential reduction in antimicrobial usage. Likewise, larger farms with higher management requirements were found to be of particular importance for the reduction of antimicrobial usage. Monitoring programs should therefore evaluate different age categories separately to identify problems for individual farms.

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.

Make science evolve into a One Health approach to improve health and security: a white paper

The World One Health Congresses are biennial gatherings of approximately 1500 professionals from relevant international organisations, OIE, FAO, WHO, World Bank, leading scientific experts and researchers in the field of One Health, animal production and trade, food safety, animal health, human health and environmentology/ecology, government representatives in public health, human health, food safety, environmental health and global health security. The Congress is organized by the One Health Platform. This white paper summarizes highlights of the 5th International One Health Congress in Saskatoon, Canada, June 2018 and serves as a roadmap for the future, detailing several concrete action points to be carried out in the run-up to the 6th World One Health Congress in Edinburgh, Scotland, June 2020.

Additive Bayesian Network analysis of associations between antimicrobial consumption, biosecurity, vaccination and productivity in Danish sow herds

In modern livestock farming, there is an increasing understanding that antimicrobial (AM) consumption must be kept low - preferably without compromising animal welfare or productivity. This requires an understanding of the relationship between AM use, productivity, biosecurity, vaccination and herd demographics. To obtain this, we undertook an Additive Bayesian Network analysis using data from 2014 to 2015, covering 157 Danish sow herds with weaners. In general, productivity and biosecurity were high, and AM consumption low. No association was found between prescribed AM and productivity. Other variables, such as biosecurity and enrolment in the Danish Specific Pathogen Free (SPF) system, had stronger associations with sow productivity than AM consumption. In the weaner unit, an association between AM consumption and certain vaccination practices was found, suggesting that vaccines might be used to control preexisting problems. The results reveal that most Danish sow producers are able to maintain productivity while using low amounts of AMs. This conclusion must be interpreted within the context of Danish pig farming i.e. generally high biosecurity and many years of official restrictions aiming at reducing AM consumption.

A register-based study on associations between vaccination, antimicrobial use and productivity in conventional Danish finisher pig herds during 2011 to 2014

Reduction of antimicrobial use (AMU) in pigs is a priority to counteract development of antimicrobial resistance in animal and human pathogens. However, there is concern that Danish pig producers complying with official AMU restrictions might experience reduced herd health and productivity in the future, if alternative strategies are not available. Vaccination has been suggested as a strategy to prevent disease and minimise the need for antimicrobial treatments. The aim of this register-based study was to assess the associations between data on vaccination, productivity and AMU in Danish finisher herds over a 4-year period following initiation of the Yellow Card, which is a restrictive AMU control scheme. For each of the years 2011 to 2014, sow herds were grouped according to purchase patterns regarding Porcine Circovirus Type 2 (PCV2) (use/no use). For the sow herds (N = 179-433), additional information of purchases of vaccines against Mycoplasma hyopneumoniae (MYC), Actinobacillus pleuropneumoniae (APP), Porcine Reproductive and Respiratory Syndrome virus (PRRS) and Lawsonia intracellularis (LAW) was included. By use of movement data, finisher herds receiving pigs from the sow herds were tracked and included in the analyses. Finisher herds (N = 40-62) with register data on productivity (i.e. average daily weight gain, feed conversion rate, mortality and lean meat percentage) and data on prescriptions of antimicrobials measured in Animal Daily Doses/100 finishers/day as well as the proportion of parenteral AMU treatments out of all treatments (AMU-ratio) were included. Univariable combinations were tested for statistically significant associations (P < 0.05) and included in multivariable linear mixed-effects model for each of the six outcome variables representing productivity (N=4) or AMU (N=2). Herd number was included as a random effect to account for the herds appearing more than once. The variables representing PCV2, enrolment in the Danish Specific Pathogen Free (SPF) system, year, herd type and herd size were included as potential confounders. Vaccination against PRRS and higher AMU for finishers were associated with increased lean meat percentage, potentially due to disease outbreaks resulting in reduced growth of the pigs and lower carcass weight at slaughter in herds with PRRS. None of the other types of vaccines was associated with any of the productivity outcomes. Vaccination against PCV2, PRRS and APP were associated with higher levels of AMU, and vaccination against LAW with a higher AMU-ratio. This may be explained as some farmers preferring to take action soon after observing disease problems. No association was found between vaccination against MYC and AMU. Herds enrolled in SPF had significantly higher average daily weight gain than non-SPF herds.

Lawsonia intracellularis: Revisiting the Disease Ecology and Control of This Fastidious Pathogen in Pigs

Lawsonia intracellularis is an anaerobic obligate intracellular bacterium infecting the small intestine and infrequently also the large intestine of pigs and other animals including hamsters and horses. The infection is characterized by proliferation, hemorrhage, necrosis, or any combination commonly referred to as "ileitis," affecting the health and production efficacy of farmed pigs. Despite decades of research on this pathogen, the pathogenesis and virulence factors of this organism are not clearly known. In pigs, prophylaxis against L. intracellularis infection is achieved by either administration of subtherapeutic levels of in-feed antibiotic growth promoters or vaccination. While the former approach is considered to be effective in L. intracellularis control, potential regulations on subtherapeutic antibiotics in many countries in the near future may necessitate alternative approaches. The potential of manipulating the gut microbiome of pigs with feed ingredients or supplements to control L. intracellularis disease burden is promising based on the current understanding of the porcine gut microbiome in general, as well as preliminary insights into the disease ecology of L. intracellularis infection accrued over the last 30 years.

Application of multiblock modelling to identify key drivers for antimicrobial use in pig production in four European countries

Antimicrobial use in pig farming is influenced by a range of risk factors, including herd characteristics, biosecurity level, farm performance, occurrence of clinical signs and vaccination scheme, as well as farmers' attitudes and habits towards antimicrobial use. So far, the effect of these risk factors has been explored separately. Using an innovative method called multiblock partial least-squares regression, this study aimed to investigate, in a sample of 207 farrow-to-finish farms from Belgium, France, Germany and Sweden, the relative importance of the six above mentioned categories or 'blocks' of risk factors for antimicrobial use in pig production. Four country separate models were developed; they showed that all six blocks provided useful contribution to explaining antimicrobial use in at least one country. The occurrence of clinical signs, especially of respiratory and nervous diseases in fatteners, was one of the largest contributing blocks in all four countries, whereas the effect of the other blocks differed between countries. In terms of risk management, it suggests that a holistic and country-specific mitigation strategy is likely to be more effective. However, further research is needed to validate our findings in larger and more representative samples, as well as in other countries.

Reliable estimation of antimicrobial use and its evolution between 2010 and 2013 in French swine farms

Background

There has been a strong implication of both the French swine industry and the national authorities on reducing the use of antimicrobials in swine production since 2010. The annual monitoring of antimicrobial sales by the French Veterinary Medicines Agency (Anses-ANMV) provides estimates but not detailed figures on actual on-farm usage of antimicrobials in swine production.

Results

In order to provide detailed information on the 2010 and 2013 antimicrobial use in the French swine industry, the methodology of cross-sectional retrospective study on a representative sample of at least 150 farms has been elected. The analysis of the collected data shows a strong and significant decrease in antimicrobial exposure of pigs between 2010 and 2013. Over three years, the average number of days of treatment significantly decreased by 29% in suckling piglets and by 19% in weaned piglets. In fattening pigs, the drop (− 29%) was not statistically significant. Only usage in sows did increase over that period (+ 17%, non-significant), which might be associated with the transition to group-housing of pregnant sows that took place at the time. Also, over that period, the use of third- and fourth generation cephalosporins in suckling piglets decreased by 89%, and by 82% in sows, which confirms that the voluntary moratorium on these classes of antimicrobials decided at the end of 2010 has been effectively implemented.

Conclusions

The methodology of random sampling of farms appears as a precise and robust tool to monitor antimicrobial use within a production animal species, able to fulfil industry and national authorities’ objectives and requirements to assess the outcome of concerted efforts on antimicrobial use reduction. It demonstrates that the use of antimicrobials decreased in the French swine industry between 2010 and 2013, including the classes considered as critical for human medicine.

Veterinary Expert Opinion on Potential Drivers and Opportunities for Changing Antimicrobial Usage Practices in Livestock in Denmark, Portugal, and Switzerland

Reducing antimicrobial use (AMU) in livestock is requested by Public Health authorities. Ideally, this should be achieved without jeopardizing production output or animal health and welfare. Thus, efficient measures must be identified and developed to target drivers of AMU. Veterinarians play a central role in the identification and implementation of such efficient interventions. Sixty-seven veterinarians with expertise in livestock production in Denmark, Portugal, and Switzerland participated in an expert opinion study aimed at investigating experiences and opinions of veterinarians about the driving forces and practices related to AMU in the main livestock sectors (broiler, dairy cattle, fattening/veal calf, and pig industry) of the aforementioned countries. Opinions on potential factors influencing the choice of antimicrobials and opportunities to reduce AMU were collected. Antibiograms are seldom used, mainly due to the time lag between testing and obtaining the results. The perceived percentage of treatment failures varied between countries and livestock sectors; however, little changes were reported over time (2005-2015). The animal health problems of each livestock sector most frequently leading to AMU did not vary substantially between countries. Mandatory official interventions (i.e., binding measures applied by national or international authorities) were highlighted as having the biggest impact on AMU. There was a variation in the experts' opinion regarding feasibility and impact of interventions both between countries and livestock sectors. Nevertheless, improved biosecurity and education of veterinarians frequently received high scores. Most veterinarians believed that AMU can be reduced. The median potential reduction estimates varied from 1% in Swiss broilers to 50% in Portuguese broilers and veal/fattening calves in all countries. We hypothesize that the differences in views could be related to disease epidemiology, animal husbandry, and socio-economic factors. A profound investigation of these disparities would provide the required knowledge for developing targeted strategies to tackle AMU and consequently resistance development. However, experts also agreed that mandatory official interventions could have the greatest impact on antimicrobial consumption. Furthermore, improvement of biosecurity and education of veterinarians, the use of zinc oxide (in pigs), improving vaccination strategies, and the creation of treatment plans were the measures considered to have the largest potential to reduce AMU. This paper can inform policymakers in Europe and countries with a similar animal production regarding their AMU policy.