Infections that are resistant against antibiotics are a universal concern. They cost up to $ 100 trillion per year in health care and global mortality will reach 10 million animals by 2050.

Gut microbiota acquire and maintain ARGs

In swine farming, antibiotics are mainly used for prophylactic and growth promotion purposes. They are consistently detected in pigs’ guts at low and sub-lethal concentrations. As a result, gut microbiota acquire and maintain ARGs and enhance the abundance of resistant bacteria.

The excretion of ARGs into the soil and water is an emerging environmental, human health, and operational concern which limits the number of effective antibiotics for therapeutic purposes.

Swine waste has a greater diversity and a higher abundance of ARGs compared to other livestock waste

Antibiotic resistance mechanisms

Major resistance mechanisms include antibiotic deactivation, extrusion through efflux pumps, and protection of targets by specific proteins. The ARGs confer resistance to several major classes of antibiotics including tetracyclines, sulfonamides, β-lactams, macrolide-lincosamidstreptogramin B, aminoglycosides, fluoroquinolone, quinolone, florfenicol, chloramphenicol, and amphenicol.

Diversity and abundance of ARGs

Swine waste has a greater diversity and a higher abundance of ARGs compared to other livestock waste. This is due to a more intensive use of antibiotics for therapeutic, prophylactic, and metaphylactic purposes. Pigs also receive higher dosages early in life.

In addition, the abundance of ARGs in pig waste varies among countries, with China being at the top of the list as the largest producer and consumer of antibiotics. Site-specific physical and chemical conditions within countries affect the abundance of ARGs propagation and attenuation dynamics, as well.

ARGs spread from pigs to humans

Antibiotic-resistant bacteria and ARGs transferr from pigs into the soil through land application of manure and waste water irrigation. They spread to aquatic environments through waste water discharge and runoff. Intracellular and free ARGs in the soil and ground water transfer to indigenous bacteria through horizontal gene transfer. Then, antibiotic-resistant bacteria reach and colonise in humans causing acute or chronic infections.

Propagation of ARGs in a new environment depends on the survival, proliferation, maintenance, replication, and gene transfer by the original host and the probability of gene acquisition by new hosts. The growth rates of antibiotic-resistant bacteria, substrate concentrations, and the presence of toxic compounds impact the occurence of ARGs in the environment.

Oral ingestion of contaminated food, waste, residual waste from occupational exposure or contaminated environments and inhalation are the pathways by which antibiotic-resistant bacteria reach human gut environments. Factors such as high concentrations and proximity of ARG donors and recipients, temperature, physiochemical conditions, and nutrient availability increase horizontal gene transfer in the human gut and cause multidrug resistance genes occurrence.

ARGs can be removed from manure by conventional waste treatment

Standard manure treatment

ARGs can be removed from manure by conventional waste treatment. The waste is stored in lagoons and then treated through anaerobic digestion or composting and it is separated into solid and liquid streams. The solids are used to fertilise agriculture soils, and the liquid is treated in a bioreactor or is discharged directly to waterbodies without treatment.

Differences in operating temperature, abilities of potential hosts to maintain and transfer ARGs, and properties of the manure affect the abundance of certain types of ARGs. Strategies including manure stabilisation with lime before application, vegetating the soil with appropriate plants, and using land application methods such as incorporation or injection mitigate ARG propagation in the soil.

Supplementing biochar and wheat straw reduces the dissolved concentration of inhibitory residual antibiotics and heavy metals, improves the digestion process and the associated removal of ARGs. Furthermore, thermophilic composting along with additives that reduce the bioavailability of heavy metals is effective in reducing the diversity and abundance of ARGs in manure.

Controlling ARG levels at the source

Strategies including adjusting animal diets to minimise disease occurrence, decreasing human-to-animal contact, optimising waste collection methods, increasing the frequency of waste collection, and creating containment areas for sick animals reduce the spread of disease, and the ARG abundance and diversity at the source.

In addition, halting antibiotic use, preventing conjugation of plasmids carrying ARGs, and promoting resistance plasmid loss decrease the ARG abundance. Using antibiotic alternatives such as antimicrobial peptides, probiotics, and prebiotics is a promising method for selective microbial control. Regulations and policy for manure storage and disposal practices should be established to reduce ARGs discharge into receiving environments. In addition, disinfection processes such as chlorination and UV disinfection remove ARGs from drinking water and municipal wastewater.

Further research

Further research is needed to develop validated models to quantitatively assess the impact of ARG dissemination from pigs on human health.

Recently, Poland’s largest supermarket chains have started offering butter at a PLN3 (US$0.68) per package, which is the lowest level seen in years. In 2022, the Polish dairy market saw a 20% rise in butter price, and in some product categories, the price exceeded PLN10 (US$2.26) per package. By lowering retail prices, supermarkets hamper margins along the entire supply chain, dairy companies warned.

“Nobody thinks about how such prices will affect farmers,” Waldemar Broś, president of the National Association of Dairy Cooperatives, told the local news outlet, Money. “For the past 2 years, the price has been at a good European average level. Now, however, not only the price of butter has dropped.”

On 24 January, a group of dairy companies sent an open letter to Henryk Kowalczyk at the Polish Agricultural Ministry asking authorities to intervene in the market. The authors warned that the industry might be heading into a collapse due to a drastic deterioration of market conditions in Poland, as well as in other markets of Central and Eastern Europe.

Another Polish dairy business union, Dairy Forum, reported that in January, small dairy companies felt increasing pressure from the retail chains to reduce prices. It is believed that retailers, in turn, are worried about a steady drop in sales of the most popular dairy products in the past several months.

In general, the drop in prices is a global trend. During the past several months, the price of exported cheese dropped from €5 to €4 per kg in key foreign markets.

Polish dairy companies also warned about a drop in the global price of a broad range of dairy products, including powdered milk, butter, powdered whey, and cheese. Broś expressed concerns that the “prices are falling every day” and that this factor could weaken Polish dairy exports.

To some extent, the drop in global prices could be attributed to lower Chinese dairy imports in the past several months, Polish dairy companies said, explaining that China is the largest purchaser of dairy products and is largely determining the price dynamics on the world’s market.

The 3-year project, led by green farming organisation LEAF (Linking Environment and Farming), and supported by the Co-op Foundation, will see farmers developing and implementing a range of sustainable, integrated farming practices.

They will focus on soil, water, air and nature to gain a better understanding of the levers for change for addressing net zero and environmental enhancement. In return, they will receive training, mentoring and technical support from external consultants and LEAF’s technical team with a focus on reducing greenhouse gas emissions.

The farmers will be working towards joining the LEAF network as its first net-zero demonstration farms and to act as hubs for training and inspiration for other farmers as they begin their transition to net zero.

Vicky Robinson, LEAF technical director, said the ground-breaking project would support forward-thinking and innovative farmers with the tools, training and technical know-how to work towards these targets, collaborating and learning from each other.

“Farmers hold a unique power to be an innovative part of the solutions to climate change. We are hugely grateful for the support of the Co-op Foundation, which will enable us to drive forward more climate-positive farming and food systems for the future health of our planet,” said Robinson.

Dairy farmers

Rachel and Richard Risdon are tenant farmers on a 150-hectare dairy farm, running a grass-based herd of 300 Friesian x Jersey cows at Bramford Speke, near Exeter, Devon, supplying milk to Arla, which has mapped the carbon footprint of the raw material from the farm.

Grass at Bramford Speke is mainly ryegrass with clover. The spring-block calving herd yields about 5,000 litres per cow. Cows are grazed rotationally on a New Zealand-style paddock system, staying outside on the clay loam over river gravel soil until late November.

The couple run a low-cost system with cows once fully housed being self-fed silage, with each consuming about 1 tonne from an open clamp face and a cake-based blend of wheat and sugar beet pulp. Cows go back out once they calve in February with about 3-5kg of concentrate and no silage.

Rachel, also a practising vet, and Richard are an innovative couple bringing their experiences of farming both in the UK and New Zealand to shape their practices today. They are keen to understand more about their carbon footprint, how to protect water courses and encourage more biodiversity on-farm.

Located in the Scottish border, Stuart Mitchell, along with his wife Kate and parents, farm a 442-hectare mixed organic farm, including 140 suckler cows with a herd of breeding deer and 50 hectares of arable land. Already incorporating low-intensity practices, the family are keen to find the right balance of productivity and understand more about their organic system on the route to net zero and beyond.

The other farmers are upland sheep farmer Bob Clark, who runs a pure-bred flock of 200 Herdwick ewes plus a flock of draft ewes crossed with Texel and Cheviot tups; fourth-generation carrot and parsnip business Huntapac, which farms 1,300 hectares from Norfolk to Inverness, and Alan, Graeme and Valerie Whyte, who farm 2,000 hectares of avocados, macadamia nuts, pecans, timber and woodland in Northern Limpopo, South Africa.

NFU approach

The UK’s National Farmers’ Union has set the ambitious target of reaching net zero greenhouse gas emissions across the whole of agriculture in England and Wales by 2040. Jonathan Wilkinson, NFU Cymru Dairy Board chairman Jonathan Wilkinson said the industry would do this through:

• Boosting productivity – for example his cows wear monitors allowing him to track their well-being and adjust their diets and farm practices.
• Carbon sequestration
• Renewable energy – his farm works with neighbouring holdings to supply slurry to mix with their poultry manure, to produce 1MW of electricity through anaerobic digestion. This produces valuable nutrients in the form of digestate, which reduces the need for artificial fertilisers.

The study was published late 2022 in the peer-reviewed scientific title Pathogens. Researchers from the German Friedrich-Loeffler-Institut teamed up with animal health scientists in Germany and the United States to figure out whether or not AI could be a method of transmission of the virus.

Virus can be transferred through AI

That is the case, they concluded. The virus can “efficiently be transferred from infected boars to naïve recipient gilts through AI.” In the scientific article, the team warned that therefore an infected boar stud presents the risk of rapidly and widely distributing ASFv within or between countries.

The researchers used the ASFv strain “Estonia 2014” for their trial. This was conducted at the high-containment facilities at the FLI in Insel Riems, Germany. They inoculated 4 boars (2 Large White boars and 2 Piétrain boars) intramuscularly. After this. blood and semen were collected every day. The virus’ genomes were detected in the semen as early as 2 days post-infection, in blood at 1 day post-infection while semen quality remained largely unaffected.

All gilts ASFv-positive

In addition, also 14 Large White gilts were included in the trial. After insemination with extended semen, 7 of 14 gilts were ASFv positive by 7 days post-insemination, and all gilts were ASFv-positive by 35 days post-insemination.

Twelve out of 13 gilts aborted at the onset of fever. A proportion of foetuses originating from the remaining gilt showed both abnormalities and replication of ASFv in foetal tissues.

The research paper was authored by Virginia Friedrichs, Eric A. Nelson, Tessa Carrau, Paul Deutschmann, Julia Sehl-Ewert, Hanna Roszyk, M. Beer and Sandra Blome, Friedrich-Loeffler-Institut, Germany; Darwin Reicks, Reicks Veterinary Research and Consulting, St Peter, MN, USA; Tobias Hasenfuss and Elisabeth Gerstenkorn, Bundes Hybrid Zucht Programm (BHZP), Dahlenburg-Ellringen, Germany; Jeffrey J. Zimmerman, Iowa State University, Ames, IA, USA; and Jane Christopher-Hennings, South Dakota State University, Brookings, SD, USA.