Hog producers work continually to keep their barns and operations free from disease-causing microorganisms. Researchers at the Prairie Swine Centre and the University of Saskatchewan, both in Saskatoon, recently evaluated whether solutions of commercially available nanoparticles applied on pig barn surfaces can effectively inhibit the growth of microorganisms and can be an alternative to conventional chemical disinfectants.
Laboratory-scale tests conducted to evaluate the effect of various types of commercially available nanoparticles on the levels of microorganisms commonly encountered in swine barn environments showed zinc oxide nanoparticles had the highest antimicrobial efficacy among all those tested.
Further experiments carried out in the barn indicated that partial filtration of barn air with a filter loaded with ZnO nanoparticles in the ventilation recirculation system achieved reduction in bioaerosol levels in the animal- and human-occupied zones.
During sanitation, a solution of 10 milligrams of ZnO nanoparticle per milliliter of water sprayed on concrete pen floor surfaces showed significant decrease in total bacterial counts on surfaces four hours after application. Microbial population, however, started to increase after new nursery pigs were brought into the room.
Findings from a previous study showed that selected nanoparticles can effectively reduce the levels of specific hazardous gases (hydrogen sulphide and ammonia) in swine barns. Since nanoparticles are also known to have antimicrobial properties, it is important to evaluate whether nanoparticles can be used in controlling the growth and airborne transmission of microorganisms in swine barns.
If proven effective, then with a single treatment application, this technology could simultaneously address concerns with hazardous gas emissions as well as the spread of diseases, both of which have great impact on the overall profitability and sustainability of a livestock production operation.
The goal of this project was to control the growth and spread of disease-causing microorganisms in swine barns using commercially available nanoparticles. Specifically, it aimed to investigate possible deployment methods that can be implemented in actual swine barns for effective use of nanoparticles to control the spread and transmission of disease-causing microorganisms during pig-rearing stages, to assess the effectiveness of nanoparticles as an alternative method for sanitation, and to conduct a technical and economic feasibility study of applying nanoparticle treatment technology in a commercial swine production operation.
Results and discussion
The inhibitory effect of 11 different types of nanoparticles was tested against representative Gram-positive (Listeria monocytogenes, Streptococcus suis) and Gram-negative organisms (Pseudomonas fluorescence and Salmonella spp.). As shown in the chart above, this screening indicated that ZnO, CaO, CaO+, MgO and MgO+ had the greatest impact on the survival of microorganisms (i.e., Zn and Mg eliminated all the surviving cells within 16 hours), whereas some of the other agents had no effect on cell number. Thus, ZnO, CaO and MgO agents were used in subsequent tests.
Actual barn evaluation
Among the three sampling locations, the total colony-forming unit (CFU) concentrations in the animal-occupied zones (about 0.5 meter from pen floor) were the highest; on average, bioaerosol levels in the animal-occupied zones of the treated chamber were 3.4 times higher than the inlet concentrations, while the control chamber values were 5.1 times higher than the corresponding inlet concentrations. Additionally, while the CFU levels in the control room showed increasing trends as the trial progressed, a slight reduction (5%) was observed in the treated chamber 10 days after the filter with ZnO nanoparticles was installed.
On day 10, mean CFU concentration in the animal-occupied zone of the treated chamber was 926 ± 207 CFU/m3 while the control chamber had 1583 ± 1458 CFU/m3. The control chamber, however, showed increasing trends until day 10.
Microbial loads on surfaces
Surfaces in the treated chamber exhibited a reduction in microbial levels 10 days after the filter with ZnO nanoparticles was installed. About 1.7, 1.3 and 1.4 log reduction was achieved in the concrete, metal and plastic surfaces, respectively, in the treated chamber relative to their corresponding day 0 values.
This reduction, however, could not be solely attributed to the application of nanoparticles in the treated chamber since the control chamber also followed the same trend. Concrete, metal and plastic surfaces in the control chamber showed about 1.5, 1.4 and 1.7 log reduction, respectively, 10 days after the filter with no nanoparticles was installed.
Treatment during sanitation
Before high-pressure washing, microbial loads on surfaces were high and extremely variable, and statistical tests revealed that the total bacterial counts in all sampling locations were not significantly different (p>0.05) from each other. On average, CFU levels during this period ranged from 2.5 x 109 CFU/mL to 4.7 x 109 CFU/mL.
These levels dropped to 6.0 x 108 CFU/mL to 1.0 x 109 CFU/mL after high-pressure washing. That could be attributed to the fact that manure and other materials deposited on the floor were removed and cleaned during the high-pressure washing activity.
However, the trends significantly (p<0.05) changed four hours after the application of disinfectants and drying. The total bacterial counts on surfaces applied with the conventional chemical disinfectant (control) started to increase while the surfaces applied with ZnO nanoparticles solution continued to decrease. The treatment with the higher concentration of ZnO nanoparticles (10 mg/mL) achieved about 97% significant reduction (p<0.05) relative to its initial concentration before high-pressure washing.
This reduction can be attributed to the effect of the ZnO nanoparticles solution applied on those concrete floor surfaces.
However, after nursery pigs were brought into the room, the total bacterial counts on all treated surfaces started to increase, with the most apparent increase observed 24 hours after the pigs were moved into the room.
In assessing the feasibility of the use of ZnO nanoparticles as part of sanitation procedures between batches of animals, the total cost associated with the application of ZnO nanoparticles was compared to the cost incurred when using the conventional chemical disinfectant. Using the application rate identified from the room-scale trials (10 mg/mL), the total amount of ZnO nanoparticles required to disinfect a 100-head grow-finish room at the end of each room cycle was estimated to be about 0.7 kg.
The time required to prepare and apply the treatment would be about three hours per cycle. In addition, the total cost for the required materials included the cost of mixing containers, weighing scale and funnels.
Summing up all these estimates, the total cost associated with ZnO nanoparticles as a disinfectant in a grow-finish stage of operation was around 86 cents per finished pig. This was nearly 10 cents per pig higher than the use of the conventional disinfectant at a total cost of 77 cents per finished pig.
The unit price per kilogram of the conventional disinfectant was slightly higher than ZnO nanoparticles, but because of its higher water solubility, the time to prepare and apply the treatment was lower than with ZnO nanoparticles.
Nevertheless, the slim margin of the total cost associated with ZnO nanoparticle solution compared to the conventional chemical disinfectant can be compensated by its effectiveness to reduce further the levels of microorganisms on surfaces when preparing the room for the next growth cycle.
Based on the findings from this study, the following conclusions can be made:
■ Specific types of commercially available nanoparticles such as ZnO nanoparticles were found to be effective in controlling the growth of selected pathogens that can be encountered in swine production environments.
■ Deploying the nanoparticles in filter systems through which barn air is passed can effectively reduce the levels of airborne bioaerosols in a pig barn. The setup can be made more effective with better capture of air in the room to pass through the filter system.
■ Sanitation procedures involving the application of nanoparticles in solution on pig barn surfaces can effectively inhibit the growth of microorganisms and can be an alternative to conventional chemical disinfectants.
■ Using current cost estimates and application parameters, the use of ZnO nanoparticle solution during sanitation was only about 10 cents more than the use of the conventional disinfectant.
Acknowledgements: Financial support for this research project came from the Saskatchewan Agriculture Development Fund, the Agriculture and Food Council of Alberta and the Saskatchewan Pork Development Board.
The authors would also like to acknowledge the strategic program funding from Sask Pork, Alberta Pork, Ontario Pork, the Manitoba Pork Council and the Saskatchewan Agriculture Development Fund. Production and research technicians at Prairie Swine Centre are also recognized for making it possible to conduct this research.