Project : USDA ARS

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Research Project: Reducing Production Losses due to Oxidative Stress and Bacterial Pathogens in Swine

Location: Agroecosystems Management Research

2020 Annual Report

Objectives
The objectives of the project are to develop an understanding of the interrelationships between non-antibiotic feed additives and pathogen translocation and shedding in growing pigs, obtain critical measures of oxidative stress in growing pigs and reproducing swine, and develop interventions to reduce or prevent pathogen colonization and disease in swine in an effort to maximize production efficiency but minimize environmental impact. Objective 1: Evaluate alternatives to antibiotics (butyric acid, resistant starch, inulin, etc.) for maintaining growth performance and reducing intestinal bacterial translocation and shedding in growing pigs. Objective 2: Determine the inherent variation in oxidative stress measures in breeding and lactating gilts, and correlate to measures of sow lifetime productivity. Objective 3: Identify markers associated with oxidative stress and correlate to changes in pig growth and feed intake, using peroxidized soybean oil as the inducer of oxidative stress. Objective 4: Determine whether vaccination of swine with a Salmonella DIVA vaccine can prevent/reduce colonization and improve growth following transmission of Salmonella from actively shedding pigs.

Approach
Alternatives to antibiotics for growing pigs will be assessed through the evaluation of compounds which have the potential to affect gastrointestinal function and microbial ecology which would, therefore, affect pig performance. Compounds to be evaluated include resistant starch, soluble dietary fiber, short- and medium-chain fatty acids, phytogenics, inorganic minerals, and beta-glucans; all of which have been suggested to affect gastrointestinal function and microbial ecology. Determination of the inherent variation in oxidative stress measures in breeding and lactating gilts will be assessed by collecting biological samples from gestating and lactating sows at 4 critical time points during these reproduction phases, and measuring key oxidative stress parameters (DNA, protein, and lipid damage) as well as antioxidant status (plasma vitamin E). In growing pigs, identification of markers associated with oxidative stress and impact on pig performance will be assessed by feeding peroxidized soybean oil to nursery, grower, or finishing pigs. Peroxidized soybean oil will be generated by heating soybean oil at 45°C for 288 h, 90°C for 72 h, or 180°C for 6 h, in comparison to unheated (22.5°C) soybean oil. Oxidative stress will be assessed measuring key oxidative stress parameters (e.g., DNA, protein, and lipid damage) as well as antioxidant status (e.g., plasma vitamin E) while performance effects will be measured by growth over a predetermined period. An attenuated Salmonella vaccine was previously designed and constructed to provide broad protection against numerous Salmonella serovars in food-producing animals. A Salmonella transmission trial will be performed in swine to determine whether vaccination against Salmonella can prevent or reduce Salmonella colonization and improve growth performance following exposure to pigs actively shedding Salmonella.

Progress Report
Research on feeding peroxidized soybean oil to pigs indicated that consumption of peroxided lipids resulted in a reduction in animal growth rate and, in some cases, increased measures of oxidative stress. Additional research was conducted with an industry cooperator and supports previously conducted research that, depending upon what temperature and how long the soybean oil was thermally processed, either peroxide value or anisidine value, or both, were predictive of the change in rates of pig performance. Research on non-antibiotic feed additives continues, including additives such as resistant starch, soluble corn fiber, protected butyrate, and other additives proposed to affect intestinal microbiota to improve or maintain gut health and animal performance. As with most of the research conducted on this topic, without any health challenge, the data suggests that these products have little impact on animal performance. Alternatives to antibiotics are sought to suppress pathogens during food-animal production to protect animal health and minimize losses in productivity. The inclusion of zinc and copper in swine diets at levels much greater than concentrations required to support optimal pig growth, have been utilized in animal production as alternatives to antibiotics. In support of Objective 1 of the Project Plan to evaluate alternatives to antibiotics in growing pigs, the ability of zinc and copper administration to reduce gastrointestinal colonization and fecal shedding of a multidrug-resistant, metal tolerant strain of Salmonella enterica serovar I 4,[5],12:i:- was assessed. The swine fecal shedding and gastrointestinal colonization of serovar I 4,[5],12:i:- was not significantly reduced in pigs administered zinc and copper at pharmacological levels compared to pigs receiving the control diet. Furthermore, the decline in the level of Salmonella fecal shedding over the duration of the study was significantly greater in control pigs compared to swine receiving elevated zinc and copper in their diet. This swine study indicates that pharmacological levels of zinc and copper as alternatives to antibiotics do not reduce gastrointestinal colonization and fecal shedding of a metal tolerant strain of Salmonella serovar I 4,[5],12:i:- and in contrast to their intended use, these metals, may prolong gastrointestinal colonization and fecal shedding of this pathogen.

Accomplishments
1. Metal tolerance genes identified in a pork outbreak-associated Salmonella strain. In 2015, a multistate outbreak of multidrug-resistant (resistance to three or more types of antimicrobials) Salmonella enterica serovar I 4,[5],12:i:- occurred due to consumption of contaminated pork and initiated a recall of 523,380 pounds of meat. Over the last decade, this Salmonella serovar has emerged as the fourth most frequent cause of human salmonellosis in the U.S. and is the most common multidrug-resistant Salmonella serovar accounting for 35% of multidrug-resistant isolates. ARS researchers in Ames, Iowa, along with colleagues at the U.S. Food Safety and Inspection Service sequenced and analyzed the genomic DNA of a multidrug-resistant serovar I 4,[5],12:i:- strain isolated from the swine processing plant involved in the 2015 pork outbreak. The presence of metal tolerance genes for copper, arsenic, silver, and mercury in addition to four sets of antimicrobial resistance genes were identified in the bacterial DNA. Recent efforts in swine production to utilize alternatives to antibiotics for suppression of disease-causing pathogens has seen the inclusion of copper (at levels greater than required for growth) as a feed additive in swine rations. Identification of numerous metal tolerance genes in a swine-associated, multidrug-resistant Salmonella serovar I 4,[5],12:i:- strain provides swine veterinarians and producers with information on the potential emergence of metal tolerant bacterial pathogens as a consequence of copper administration at pharmacological levels in the swine diet.

U.S. DEPARTMENT OF AGRICULTURE

Agroecosystems Management Research: Ames, IA