Pig farms’ own practices affect the resistance to antibiotics in the pork production chain

Pig farms’ own treatment practices and protective measures against pathogens play a key role in combating antimicrobial resistance in the pork production chain. This is shown by the joint study by the Finnish Food Authority and the University of Helsinki, which monitored the antibiotic resistance of the E. coli bacteria that are a part of the normal intestinal bacterial flora of animals during the different stages of the pig production chain. The results of the study can be used in instructions targeted at the producers and in the planning of antibiotic resistance risk management measures.

The study included ten volunteer combination piggeries or chains from pig production to pig fattening houses. Samples were taken twice from live pigs: once from five-week-old pigs after weaning and again before the pigs were slaughtered at approximately 22 weeks of age. The highest level of resistance was discovered in the samples taken after weaning, but it decreased considerably by the sampling before slaughter. There was variation between the farms, however.

“According to the research plan, one litter of pigs that received antibiotics and a corresponding group of pigs that was not treated with antibiotics at any point or in snout contact with the medicated pigs were studied at each farm. Because only individual animals were treated with antibiotics in the end, it was not possible to get the planned number of samples from pigs treated with antibiotics from every farm”, says Docent Johanna Suomi, PhD, Finnish Food Authority.

Good slaughter hygiene affects the meat

Samples from the pigs being studied were also taken at the slaughterhouse: swabs were taken from the surface of the carcases after slaughter and meat samples were taken at the meat cutting plant. E.coli bacteria was not isolated from all of the samples taken at the slaughterhouse. However, resistance was also found in the bacteria isolated from the carcase and meat samples taken at the slaughterhouse.

“Good slaughter hygiene can prevent or reduce the transfer of intestinal bacteria to meat, which also reduces the transfer of antibiotics-resistant bacteria. Nevertheless, this study discovered E. coli bacteria resistant to several antibiotics in some of the meat samples. For this reason, all measures taken at the farms to reduce resistance are important”, says Senior Researcher Suvi Nykäsenoja, Finnish Food Authority.

Practical measures taken by the pig farms are important for prevention

“Based on the statistical analyses I conducted, the use of antibiotics alone did not have an effect on whether resistance to antibiotics was found in the E. coli bacteria isolated from pigs or not, or how the potential resistance changed between the weaning stage and the slaughtering line. The results hint that by improving the biosecurity of the farms, the resistance of the bacteria in production animals could also be reduced. In my opinion, this connection should be studied further”, says Johanna Muurinen, PhD, Purdue University, who acted as a project researcher.

The biosecurity of the farms that participated in the study, i.e. the measures taken to reduce the risk of arrival and spread of diseases, was generally at a lower level than in Finnish farms on average. There was more variation between the farms regarding their internal biosecurity, meaning the measures taken to prevent the spread of diseases within the farm, than their external biosecurity, meaning the measures taken by farmers to prevent the spread of diseases from external sources to the farm.

“Similar studies conducted abroad have discovered a connection between biosecurity and the use of antimicrobials, even though no causal relationship has been found. The use of antimicrobials is not a direct indication of increased resistance, however. Then again, it might not be possible to get clear results in Finland even with a larger sample size, because the use of antibiotics in production animals is already at a lower level than in many countries in Central and Southern Europe to begin with. In addition, a lot of the studies on biosecurity and the use of medications have been carried out concerning the preventive use of antibiotics; as a rule, this does not happen in Finland thanks to the good system of health care for production animals”, says Doctoral Student Virpi Sali, University of Helsinki.

The level of protection against pathogens at the farms was studied with an international questionnaire (BiocheckU.GentTM), which was developed to assess both internal and external biosecurity.

“When interpreting the results, it must be noted that the questionnaire used was developed for a situation concerning animal diseases that differs from the fairly good Finnish situation. The threats from outside the farm are typically understood well at Finnish farms, but there is less investment in preventing the spread of pathogens within the farm. As a result, the level of internal protection against pathogens at Finnish farms is generally lower than average”, says Sali.

The choice of medications does not always follow the health care plans

For a long time, recommendations for the use of antimicrobials have been issued in Finland for veterinarians. The objective of the recommendations is to ensure that the resistance situation is managed as well as possible. The more people deviate from the recommendations for the use of antimicrobials, the more difficult the management becomes.

The realisation of the use of medications instructed in the health care plans of the farms studied was investigated based on the Sikava database. Farms belonging to the Finnish pork quality system are obliged to enter the medication data of the animals into the database.

There was some variation between the farms’ health care plans. There were differences in the medications prescribed to treat the most common illnesses of pigs, such as arthritis and intestinal infections. However, the differences in the treatment of arthritis may be partly explained by the problems with the availability of penicillin during the data collection period. All farms had at least two different options for medications to treat arthritis. There were also different instructions on the medication for diarrhoea based on different pathogens, since the symptoms are often clear, but there are many potential pathogens. In accordance with the recommendations, infections due to tail biting were treated almost solely by penicillin.

“In the E. coli bacteria acting as indicator of the resistance situation, the most commonly found resistance was to tetracyclines, sulfonamides, trimethoprim or aminopenicillins. Bacteria resistant to several different antibiotics were also common, meaning that roughly one half of all resistant E. coli strains were resistant to at least two of the medications mentioned above. If similar resistance is found in pathogenic bacteria, the range of medications available is small, and it may be necessary to use antibiotics such as fluoroquinolones in the treatment that are particularly problematic with regard to resistance”, Nykäsenoja says.

The study was conducted in cooperation between the Risk Assessment Unit and the Microbiology Unit of the Finnish Food Authority and the Faculty of Veterinary Medicine of the University of Helsinki. The study was funded by the Development Fund of Agriculture and Forestry (Makera).

The results of the project will be published later as scientific articles and reports. An information package on resistance for producers will be drawn up and published during 2019.

Learn more about the project Control and prevention of antimicrobial resistance in the pork production chain 

For more information, please contact:
20 March 2019, 3 p.m. o’clock at the earliest.

Senior Researcher Johanna Suomi, study design for the project, tel. +358 40 822 5629, Finnish Food Authority
Senior Researcher Suvi Nykäsenoja, research on antibiotic resistance, tel. +358 40 489 3447, Finnish Food Authority
Postdoctoral Researcher Johanna Muurinen, statistical analyses, effects of practices and protection against pathogens on the incidence of resistance and the use of medications, smuurine@purdue.edu, Purdue University, West Lafayette, United States
Doctoral Student Virpi Sali, protection against pathogens at farms, virpi.sali@helsinki.fi, Faculty of Veterinary Medicine, University of Helsinki