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

2021 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
Objective 1: Research on non-antibiotic feed additives such as resistant starches, soluble fibers, protected short-chain fatty acids, phytogenic compounds, and short- and medium-chain fatty acids are proposed to affect intestinal microbiota and ultimately improve or maintain gut health and animal performance. Research conducted in young pigs on each of these in-feed additives concluded that these products have little impact on animal productivity when tested in a university/research-based setting in the absence of a health challenge. Objective 2: Metals are frequently used in animal feed during the early stages of swine production as alternatives to antibiotics to suppress pathogens, protect animal health, and minimize losses in productivity. Research evaluating the use of metals as alternatives to antimicrobials in swine production demonstrated that inclusion of elevated levels of copper and zinc in the animal feed did not significantly reduce colonization of a multidrug-resistant (resistance to three or more antimicrobial classes), metal tolerant Salmonella enterica serovar I 4,[5],12:i:- strain USDA15WA-1 associated with a 2015 U.S. pork outbreak. Genomic analysis of serovar I 4,[5],12:i:- strains isolated from food animals (swine, bovine, chicken, and turkey) in the U.S. was performed to determine the presence of antimicrobial resistance and metal tolerance genes similar to the pork outbreak-associated serovar I 4,[5],12:i:- strain USDA15WA-1. Serovar I 4,[5],12:i:- isolates from swine were significantly more likely to contain both antimicrobial resistance and metal tolerance genes compared to strains associated with other food animals. Due to the association of multidrug-resistant, metal tolerant Salmonella enterica serovar I 4,[5],12:i:- isolates with swine, future research to evaluate alternatives to antibiotics to enhance animal production should focus on feed additives that are not dependent upon metals for suppression of pathogens. Objective 3: Pigs fed soybean oil containing lipid oxidation products which were generated by heating soybean oil at various elevated temperatures with continuous air diffusion into the oil during heating resulted in a substantial reduction in rate of gain and levels of feed intake in nursery, growing, and finishing pigs. Chemical analysis of the lipid oxidation products in the oil suggested that either peroxides or aldehydes in the oil, or both, are highly correlated to this reduction in pig performance, but that measures of oxidative stress (i.e., lipid, DNA, or protein damage) within the animal are not indicative of consumption of these peroxidized oils or of the reduction in animal performance.

Accomplishments
1. Characterization of metal tolerance in a pork outbreak-associated Salmonella strain. Characterization of metal tolerance in a pork outbreak-associated Salmonella strain. High levels of copper and zinc are frequently included in the diets of young pigs as alternatives to antimicrobials to decrease pathogens and increase animal growth during food-animal production, but the use of copper or zinc may promote metal tolerance in bacterial pathogens resulting in decreased effectiveness for pathogen control. A Salmonella strain associated with a 2015 U.S. pork outbreak contained multiple metal tolerance genes on a movable genetic element. The metal tolerance of the Salmonella strain was assessed in multiple ways including bacterial growth, gene transfer, and pig colonization. ARS researchers in Ames, Iowa, demonstrated multiple findings. The pork outbreak-associated Salmonella strain had increased tolerance to the metals copper, arsenic, and antimony. The metal tolerance element in this Salmonella strain can be transferred to other bacterial isolates resulting in increased metal tolerance in the recipients. Because the Salmonella strain is metal tolerant, the use of elevated levels of zinc and copper as alternatives to antimicrobials in the animal diet did not decrease pig colonization by the pathogen. This research provides information to veterinarians, swine producers, and microbiologists that certain Salmonella strains present in the U.S. pig population have increased tolerance to copper used in animal production, and the presence of metal tolerance genes in bacterial populations may limit the effectiveness of metals used to control disease.

2. Enteric challenges have inconsistent effects on in vivo markers of oxidative stress. Oxidative status relates to the balance between free radicals or reactive species (oxygen-, nitrogen-, or sulfur-based) and the antioxidant defense system within an organism. Because free radicles or reactive species need electrons to become less reactive, they scavenge electrons from proteins, lipids, or DNA. If the presence of free radicals overwhelms the antioxidant defense system, protein, lipid, or DNA damage can occur leading to ‘oxidative stress’ in the animal. Literature has shown that consumption of mycotoxins, oxidized proteins, or peroxidized lipids can have negative effects on animal performance, where it is theorized that some of this negative effect is due to these compounds causing oxidative stress. ARS researchers in Ames, Iowa, demonstrated that while consumption of mycotoxins, oxidized proteins, and peroxidized lipids did in fact reduce animal performance, the effects of these compounds altering specific markers of oxidative stress (e.g., protein, lipid, or DNA damage indices) were inconsistently affected suggesting that oxidative stress was not a major mechanism for the reduction in performance that was observed. This research will assist the scientific community on determining which mechanistic measures are best suited, or not suited, in defining how oxidative status relates to animal performance.

U.S. DEPARTMENT OF AGRICULTURE

Agroecosystems Management Research: Ames, IA