Effects of the novel concept 'outdoor veal calf' on antimicrobial use, mortality and weight gain in Switzerland

Interventions to change antimicrobial use in livestock: A scoping review and an impact pathway analysis of what works, how, for whom and why

Antimicrobial resistance (AMR) is a public health threat responsible for 700,000 deaths per year worldwide. Antimicrobial use (AMU) in livestock contributes to AMR in animal and public health. Therefore, it is essential to implement effective interventions towards better AMU in livestock. However, there is a lack of evidence to inform decision-makers of what works, how, for whom and why and how effective interventions can be adapted to different contexts. We conducted a scoping review and an impact pathway analysis to systematically map the research done in this area and to inform evidence-based and context-appropriate policies. We followed the PRISMA-ScR requirements and searched Web of Science, PubMed and Scopus databases to identify studies in English or French languages, in open access and published between 2000 and 2022. We selected thirty references addressing twenty-eight different interventions that were successful in changing AMU in livestock. We used an impact pathway logic model as an analytic framework to guide the technical aspects of the scoping review process and to identify the complex relationships between outputs, outcomes, impacts and contextual factors. A majority of interventions managed to improve AMU by changing herd and health management practices (ni=18). We identified intermediate outcomes including change in the veterinarian-farmer relationship (ni=7), in knowledge and perception (ni=6), and in motivation and confidence (ni=1). Twenty-two studies recorded positive impacts on animal health and welfare (ni=11), technical performances (ni=9), economic performances (ni=4) and AMR reduction (ni=4). Interventions implemented different strategies including herd and health management support (ni=20), norms and standards (ni=11), informational and educational measures (ni=10), economic support (ni=5). Studies were mainly in European countries and in pig and large ruminants farming. Most interventions targeted farmers or veterinarians but we identified other major and influential actors including authority and governmental organizations, academics and research, organization of producers or veterinarians, herd advisors and technicians, laboratories, and public opinion. Key success factors were knowledge and perception (ni=14), social factors (ni=13), intervention characteristics (ni=11), trajectory and ecosystem of change (ni=11), economic factors (ni=9), herd and health status (ni=8), data access and monitoring (ni=4). This review describes a paucity of impact assessment of interventions towards better AMU in livestock. There is no one-size-fits-all transition pathway but we inform decision-makers about the most successful interventions that work, how, for whom and why. The impact pathway analysis provided a holistic view of the successful change processes and the complex relationships between outputs, outcomes, impacts and contexts.

Oxazolidinone resistance genes in florfenicol-resistant enterococci from beef cattle and veal calves at slaughter

Background

Linezolid is a critically important oxazolidinone antibiotic used in human medicine. Although linezolid is not licensed for use in food-producing animals, the use of florfenicol in veterinary medicine co-selects for oxazolidinone resistance genes.

Objective

This study aimed to assess the occurrence of cfr, optrA, and poxtA in florfenicol-resistant isolates from beef cattle and veal calves from different herds in Switzerland.

Methods

A total of 618 cecal samples taken from beef cattle and veal calves at slaughter originating from 199 herds were cultured after an enrichment step on a selective medium containing 10 mg/L florfenicol. Isolates were screened by PCR for cfr, optrA, and poxtA which are genes known to confer resistance to oxazolidinones and phenicols. One isolate per PCR-positive species and herd was selected for antimicrobial susceptibility testing (AST) and whole-genome sequencing (WGS).

Results

Overall, 105 florfenicol-resistant isolates were obtained from 99 (16%) of the samples, corresponding to 4% of the beef cattle herds and 24% of the veal calf herds. Screening by PCR revealed the presence of optrA in 95 (90%) and poxtA in 22 (21%) of the isolates. None of the isolates contained cfr. Isolates included for AST and WGS analysis were Enterococcus (E.) faecalis (n = 14), E. faecium (n = 12), E. dispar (n = 1), E. durans (n = 2), E. gallinarum (n = 1), Vagococcus (V.) lutrae (n = 2), Aerococcus (A.) urinaeequi (n = 1), and Companilactobacillus (C.) farciminis (n = 1). Thirteen isolates exhibited phenotypic linezolid resistance. Three novel OptrA variants were identified. Multilocus sequence typing identified four E. faecium ST18 belonging to hospital-associated clade A1. There was a difference in the replicon profile among optrA- and poxtA-harboring plasmids, with rep9 (RepA_N) plasmids dominating in optrA-harboring E. faecalis and rep2 (Inc18) and rep29 (Rep_3) plasmids in poxtA-carrying E. faecium.

Conclusion

Beef cattle and veal calves are reservoirs for enterococci with acquired linezolid resistance genes optrA and poxtA. The presence of E. faecium ST18 highlights the zoonotic potential of some bovine isolates. The dispersal of clinically relevant oxazolidinone resistance genes throughout a wide variety of species including Enterococcus spp., V. lutrae, A. urinaeequi, and the probiotic C. farciminis in food-producing animals is a public health concern.

Associations of antimicrobial use with antimicrobial susceptibility at the calf level in bacteria isolated from the respiratory and digestive tracts of veal calves before slaughter

Objectives

Antimicrobial drugs are frequently administered in veal calves, but investigations on associations with antimicrobial susceptibility of bacteria are scarce and convey partly contradictory findings. The aim of this study was to investigate associations of antimicrobial use (AMU) during the fattening period with antimicrobial susceptibility shortly before slaughter.

Methods

Detailed treatment data of 1905 veal calves from 38 farms were collected prospectively during monthly farm visits for 1 year (n = 1864 treatments, n = 535 visits); 1582 Escherichia coli, 1059 Pasteurella multocida and 315 Mannheimia haemolytica were isolated from rectal and nasopharyngeal swabs collected before slaughter and subjected to antimicrobial susceptibility testing by microdilution. Associations of antimicrobial treatments with resistant isolates were investigated at the calf level.

Results

Associations of AMU with antimicrobial resistance were observed using generalized linear models. For E. coli, the odds of being resistant were increased with increased AMU (OR 1.36 when number of treatments >1, P = 0.066). Use of tetracyclines was associated with resistance to tetracycline (OR 1.86, P < 0.001) and use of penicillins was associated with resistance to ampicillin (OR 1.66, P = 0.014). No significant associations were observed for P. multocida (use of aminoglycosides: OR 3.66 for resistance to spectinomycin, P = 0.074). For M. haemolytica, the odds of being resistant were increased with increased AMU (OR 4.63, P < 0.001), and use of tetracyclines was associated with resistance to tetracycline (OR 6.49, P < 0.001).

Conclusions

Occurrence of resistant bacteria shortly before slaughter was associated with AMU in veal calves. Prudent and appropriate use may contribute to limit the selection of resistant bacteria on veal farms.

The use of common antimicrobial agents in US veal calves

The use of antimicrobials in food animals and the selection of antimicrobial-resistant pathogens continue to be prominent concerns for human food safety and public health. To provide optimal stewardship programs, antimicrobial use in animal production operations must be quantified and standardized for benchmarking and creating goals, monitoring temporal trends, and identifying causes of emerging resistance. In the United States, quantified estimates of antimicrobial use are available in dairy and beef cattle, but these data have not been generated for veal calf herds. Therefore, the objective of this study was to estimate the treatment incidence (TI) of antimicrobials for eight US veal calf farms in one rearing cycle. Treatment incidences were compared between calculated doses defined by the labeled daily dose (LDD), animal-defined daily dose (ADD) from the European Medicines Agency (EMA) guideline, and the used daily dose (UDD) from the farm treatment protocols. Among eight farms, veal calves received a mean of 34.40 LDD, 34.88 ADD, and 28.68 UDD of an antimicrobial per 100 days. The lower TI based on the UDD administration was a result of higher farm protocol dosing relative to the labeled and EMA daily doses. Higher quantities of antimicrobial administration were observed in the first three weeks (day 1-21) of rearing (Tukey-adjusted p < .05). This study is the first to quantitatively estimate the TI of antimicrobials on the US veal calf operations and serves as an important step toward the development of antimicrobial stewardship programs.

Screening of Antimicrobial Activity of Essential Oils against Bovine Respiratory Pathogens - Focusing on Pasteurella multocida

Administration of essential oils as natural plant products with antimicrobial activity might be an alternative to antibiotic treatment of bovine respiratory disease. The aim of this study was to analyse the in vitro antimicrobial activity of 11 essential oils against Pasteurella multocida isolated from the respiratory tract of calves using microdilution with determination of minimum inhibitory and bactericidal concentration as well as agar disc diffusion. Additionally, antimicrobial activity against Mannheimia haemolytica and bacteria in the Mannheimia clade was assessed by agar disc diffusion. Seven essential oil mixtures were also tested against all bacterial isolates. P. multocida was strongly inhibited by cinnamon cassia and lemongrass oil followed by coriander, winter savory, thyme, clove, and peppermint oil in the microdilution assays. Eucalyptus, wintergreen, spruce, and star anise oil showed lower activity. Comparison of both methods revealed an underestimation of cinnamon cassia oil activity by agar disc diffusion and conflicting results for wintergreen oil in microdilution, which precipitated in broth. Cinnamon cassia, thyme, wintergreen, lemongrass, and winter savory oil all showed strong antimicrobial activity against M. haemolytica. Bacteria in the Mannheimia clade were mostly inhibited by cinnamon cassia and thyme oil. Pasteurella isolates were more susceptible to inhibition by essential oils than Mannheimia isolates. Essential oil mixtures did not show stronger antibacterial activity than single essential oils. In conclusion, cinnamon cassia and lemongrass as well as coriander, winter savory, and thyme oil are promising candidates for treatment of P. multocida-associated bovine respiratory infections.

Promoting Judicious Antimicrobial Use in Beef Production: The Role of Quarantine

Judicious antimicrobial stewardship in livestock industry is needed to reduce the use of antimicrobials (AMU) and the associated risk of antimicrobial resistance. Biosecurity measures are acknowledged for their role against the spread of diseases and the importance in reducing AMU in different species. However, their effectiveness in beef production has been scarcely considered. The aim of this study was to investigate the effect of the quarantine strategy on AMU in beef cattle. A total of 1206 Charolaise animals in five farms were included in the trial. Roughly half of the animals followed the standard procedure of the fattening cycle (no-quarantine; NO-QUA group) and half followed a 30-day period of quarantine (QUA group) since their arrival. Performance and antimicrobial data were recorded and a treatment incidence 100 (TI100it) per animal was calculated. Penicillins was the most used class of antimicrobials. Differences between groups were significant for males only, with NO-QUA group having greater TI100it (3.76 vs. 3.24; p < 0.05) and lower body weight at slaughter (713.4 vs. 723.7 kg; p < 0.05) than QUA group. Results suggest that quarantine strategy can reduce AMU in males without compromising their performance, whereas further investigation is needed for females.

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

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

Comparison of Antimicrobial Treatment Incidence Quantification Based on Detailed Field Data on Animal Level with the Standardized Methodology of the European Medicines Agency in Veal Calves, Switzerland, 2016-2018

Precise quantification of antimicrobial treatment incidence (TI) is crucial for benchmarking. Two widespread methods for treatment incidence quantification were compared for agreement. Field data were obtained from 38 veal farms from 2016 to 2018 (1905 calves, 1864 treatments). Calculation of TI_swiss for calves was based on detailed treatment records using pharmacokinetic values from the Swiss Veterinary Medicines Compendium. The method published by the European Medicines Agency was used to calculate TI in defined daily doses (TI_DDD). For each calf and treatment, TI_swiss and TI_DDD were calculated on level of the antimicrobial class, drug, application route, and farm. The quotient (Q) of TI_swiss and TI_DDD was calculated. Divergence in results between the two methods of ≤25% was arbitrarily set as good agreement. The agreement between TI_swiss and TI_DDD was mostly good. On class level, good agreement was observed for treatments representing 71.5% of the TI_DDD, and 74.5% of the total TI_DDD on drug level. Poor agreement was mainly observed for tylosin and sulfadimidine. The agreement was better for parenteral than for oral treatments (81.6% vs. 72.3%). For practically orientated calculation on farm level, good agreement was observed (77.5% of the TI_DDD). The TI_DDD method showed mostly good agreement, especially for parenteral treatments.

Prevalence of BRD-Related Viral Pathogens in the Upper Respiratory Tract of Swiss Veal Calves

The prevention of bovine respiratory disease is important, as it may lead to impaired welfare, economic losses, and considerable antimicrobial use, which can be associated with antimicrobial resistance. The aim of this study was to describe the prevalence of respiratory viruses and to identify risk factors for their occurrence. A convenience sample of 764 deep nasopharyngeal swab samples from veal calves was screened by PCR for bovine respiratory syncytial virus (BRSV), bovine parainfluenza-3 virus (BPI3V), bovine coronavirus (BCoV), influenza D virus (IDV), and influenza C virus (ICV). The following prevalence rates were observed: BRSV, 2.1%; BPI3V, 3.3%; BCoV, 53.5%; IDV, 4.1%; ICV, 0%. Logistic mixed regression models were built for BCoV to explore associations with calf management and housing. Positive swab samples were more frequent in younger calves than older calves (>100 days; p < 0.001). The probability of detecting BCoV increased with increasing group size in young calves. Findings from this study suggested that young calves should be fattened in small groups to limit the risk of occurrence of BCoV, although an extended spectrum of risk factors for viral associated respiratory disorders such as nutritional aspects should be considered in future studies.

Pollution by Antibiotics and Antimicrobial Resistance in LiveStock and Poultry Manure in China, and Countermeasures

The demand for animal protein has increased considerably worldwide, especially in China, where large numbers of livestock and poultry are produced. Antibiotics have been widely applied to promote growth and prevent diseases. However, the overuse of antibiotics in animal feed has caused serious environmental and health risks, especially the wide spread of antimicrobial resistance (AMR), which seriously affects animal and human health, food safety, ecosystems, and the sustainable future development of animal protein production. Unfortunately, AMR has already become a worldwide challenge, so international cooperation is becoming more important for combatting it. China’s efforts and determination to restrict antibiotic usage through law enforcement and effective management are of significance. In this review, we address the pollution problems of antibiotics; in particular, the AMR in water, soil, and plants caused by livestock and poultry manure in China. The negative impact of widespread and intensive use of antibiotics in livestock production is discussed. To reduce and mitigate AMR problems, we emphasize in this review the development of antibiotic substitutes for the era of antibiotic prohibition.

Income compensation options and partial budget analysis following a reduction of antimicrobial sales at the veterinary practice level

Over the years, the excessive consumption of antimicrobials (AM) by animals and humans has become a major concern at the global level, and several studies have highlighted the link between antimicrobial use (AMU) and antimicrobial resistance. Previous studies showed that, in Switzerland, every calf in the fattening process received in average seven days of AM treatment, and mainly oral group treatments. Therefore, policies to reduce the consumption of AM among veal calves should be implemented and promoted to decrease AM pressure on the microbiome. This study aimed to assess how a potential loss of income due to a reduction of AM prescriptions and sales in the Swiss veal calves sector could potentially be compensated. Partial budget models at the veterinary practice level were built to evaluate the effect on the net profit of veterinary practices, following four different national policy interventions that aim to reduce AM prescriptions for veal calves. The best-case scenarios resulted in a positive net profit. The scenarios assuming complete loss of profit from AM sales resulted in very low or negative net profit. Therefore, without financial support (e.g. through the government or other entities), veterinarians are likely to find it difficult to fully compensate the economic losses. At the practice level, income compensation mechanisms require a fundamental change of the business model. New model should be largely independent of pharmaceutical sales and should promote paid counselling on herd health management.

Perspectives on the Management of Surplus Dairy Calves in the United States and Canada

The care of surplus dairy calves is a significant issue for the United States and Canadian dairy industries. Surplus dairy calves commonly experience poor welfare as evidenced by high levels of mortality and morbidity, and negative affective states resulting from limited opportunities to express natural behaviors. Many of these challenges are a result of a disaggregated production system, beginning with calf management at the dairy farm of origin and ending at a calf-raising facility, with some calves experiencing long-distance transportation and commingling at auction markets or assembly yards in the interim. Thus, the objectives of this narrative review are to highlight specific challenges associated with raising surplus dairy calves in the U.S. and Canada, how these challenges originate and could be addressed, and discuss future directions that may start with refinements of the current system, but ultimately require a system change. The first critical area to address is the management of surplus dairy calves on the dairy farm of origin. Good neonatal calf care reduces the risk of disease and mortality, however, many dairy farms in Canada and the U.S. do not provide sufficient colostrum or nutrition to surplus calves. Transportation and marketing are also major issues. Calves can be transported more than 24 consecutive hours, and most calves are sold through auction markets or assembly yards which increases disease exposure. Management of calves at calf-raisers is another area of concern. Calves are generally housed individually and fed at low planes of nutrition, resulting in poor affective states and high rates of morbidity and mortality. Strategies to manage high-risk calves identified at arrival could be implemented to reduce disease burden, however, increasing the plane of nutrition and improving housing systems will likely have a more significant impact on health and welfare. However, we argue the current system is not sustainable and new solutions for surplus calves should be considered. A coordinated and holistic approach including substantial change on source dairy farms and multiple areas within the system used to market and raise surplus dairy calves, can lead to more sustainable veal and beef production with improved calf outcomes.

Effect of welfare standards and biosecurity practices on antimicrobial use in beef cattle

Antimicrobial use (AMU) in livestock species and the associated antimicrobial resistance are a global concern, thus strategies for their reduction and a more judicious use are needed. Previous research has revealed a link between improved animal welfare, biosecurity and AMU reduction in pig and dairy sectors, however, little is known about the beef sector. This study aimed to investigate the impact of welfare standards and biosecurity on AMU in beef cattle. Data on performance traits and AMU were collected over a 3.5 year time from 27 specialised beef farms and a treatment incidence was calculated using the defined daily dose for animals. An on-farm assessment was carried out by assigning a score from 0 (very poor) to 100% (very good) to 3 sections: welfare, biosecurity and emergency management. The highest average score was obtained for the welfare section (76%) followed by emergency management (39%) and biosecurity (24%). This suggests that major focus on strategies for the implementation of biosecurity measures and emergency management is needed, due to the low scores reported. A statistically significant lower AMU was observed with improved level of welfare. These results may be helpful for farm benchmarking and highlight the importance of improved animal welfare for an efficient antimicrobial stewardship.

Welfare Assessment in Calves Fattened According to the "Outdoor Veal Calf" Concept and in Conventional Veal Fattening Operations in Switzerland

Simple Summary

Antimicrobial use in humans and animals leads to the selection of resistant bacteria, a serious threat to human and animal health, as such bacteria can lead to treatment failure and death. With the “outdoor veal calf” concept, a novel calf fattening system was developed that allows for reducing antimicrobial use by 80% through improvements in management and housing, such as health check before purchase, short transport, vaccination, quarantine in individual hutches, and fattening in small groups in a roofed, straw-bedded paddock with a group hutch for shelter. In that system, veal calves spend their entire lives outdoors in the fresh air. In our study, we wanted to make sure that the observed reduction in antimicrobial treatments was not achieved at the cost of animal welfare, i.e., that sick animals were not left without treatment in order to obtain better figures for treatment reduction. Our results show that calves in the “outdoor veal calf” system had fewer signs of respiratory and digestive diseases than control calves and that their lungs had fewer lesions of pneumonia than controls after slaughter. Thus, not only was antimicrobial use drastically reduced, but calf health was really improved in the new “outdoor veal calf” system.

Abstract

The “outdoor veal calf” system was developed to encounter the demand for a veal fattening system that allows for reducing antimicrobial use without impairing animal welfare. Management improvements including direct purchase, short transportation, vaccination, three-week quarantine in individual hutches, and open-air housing in small groups in a roofed, straw-bedded paddock with a group hutch were implemented in a prospective intervention study (1905 calves, 19 intervention and 19 control farms, over one year): antimicrobial use was five times lower in "outdoor veal" farms compared to control farms (p < 0.001), but it was crucial to ensure that antimicrobial treatment reduction was not associated with decreased animal welfare, i.e., that sick animals were not left untreated. Welfare was assessed monthly on the farms, and organs of 339 calves were examined after slaughter. Cough and nasal discharge were observed significantly (p ≤ 0.05) less often in intervention than in control farms, mortality (3.1% vs. 6.3%, p = 0.020) and lung lesion prevalence (26% vs. 46%, p < 0.001) were lower; no group difference was seen in abomasal lesion prevalence (65% vs. 72%). Thus, besides reduced antimicrobial use, calf health and welfare were improved in "outdoor veal calf" farms in comparison to traditional operations.