Enteric inducers of oxidative stress and their effects on growth performance, intestinal morphology, digestibility and oxidative biomarkers in pigs
Date
2021-08
Authors
Wilson, Victoria Claire
Major Professor
Advisor
Kerr, Brian J
Greiner, Laura L
Selsby, Joshua
Committee Member
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Abstract
Livestock species are susceptible to chemical, environmental, and nutritional stressors that have the potential to negatively impact growth, health status, and homeostatic physiology. Enteric stressors such as the consumption of peroxidized oils or mycotoxins (MTX) have a clear and consistent negative impact on growth performance in monogastric species. In addition, some literature suggests that these enteric stressors also induce oxidative stress. Oxidative stress is the imbalance of oxidants and antioxidants in vivo. Oxidants occur endogenously as apart of cellular respiration, inflammatory responses, and other cellular processes. Oxidants can also come from exogenous sources in the diet or the environment. When an animal undergoes oxidative stress, oxidants that are not reduced by an antioxidant scavenge for electrons causing damage to lipid, protein, or DNA molecules.
Previous literature suggests thermally processing a protein feedstuff beyond typical production methods can lead to protein oxidation, and when consumed by an animal, could induce oxidative stress. Similarly, extensive lipid peroxidation research shows that with heating and adding oxygen to a lipid, peroxidation occurs; and when consumed by an animal may reduce growth performance and induce oxidative stress. A naturally occurring challenge to animals can be the consumption of MTX; specifically, deoxynivalenol (DON) in the Midwest United States. Swine facing the afore mentioned enteric challenges are at risk for a negative impact on performance and oxidative stress. In commercial swine operations, a single biomarker to measure would be desirable as a tool to predict herd oxidative status and potential growth losses because it would be minimally invasive and cost effective.
Therefore, the first objectives of this thesis were to better understand how oxidizing a protein is achieved and the impacts of feeding such protein (i.e., thermally processed spray-dried egg whites, TP-SDEW) on growth performance, intestinal morphology, digestibility, and oxidative stress biomarkers in nursery pigs. The second objective was to determine if feeding varied levels of DON would decrease growth performance, impair intestinal integrity, and negatively impact oxidative stress biomarkers in nursery pigs. The third objective was to determine interactive effects, if any, between feeding 15-acetyl-DON (15-A-DON), TP-SDEW, and peroxidized soy oil (PSO) on growth performance, intestinal morphology, apparent total tract digestibility (ATTD) of gross energy (GE) nitrogen (N) and sulfur (S), and oxidative stress biomarkers in nursery pigs, and to determine is specificity within oxidative stress biomarkers to specific enteric challenge exist.
The first objective was investigated (CH 2) starting with a preliminary study to determine methods of oxidizing a protein, where it was found that heating spray-dried egg white (SDEW) to 100°C for 120 h achieved the greatest amount of protein carbonylation (PC). A feeding study was subsequently conducted with 32 barrows (7 kg initial body weight (BW), 7 d post wean) with pigs assigned one of three dietary treatments: 12% SDEW, 6% SDEW and 6% TP-SDEW, or 12% TP-SDEW. The experiment lasted 24 d for collection of growth performance data and the collection of plasma and liver tissues to analyze for markers of oxidative stress. Feces were collected from each pig on d 21 to determine ATTD of N, S, and GE. Average daily gain (ADG; P = 0.76), average daily feed intake (ADFI; P = 0.57) and gain to feed ratio (GF; P = 0.83) were not found to be different among pigs fed the dietary treatments. While there was no impact of TP-SDEW on ATTD of GE (P = 0.67) or ATTD of N (P = 0.11), ATTD of S (P = 0.03) was found to increase with increasing amount of TP-SDEW in the diet. An increase in plasma carbonyl concentration (P = 0.02) was observed in pigs fed 12% TP-SDEW compared to pigs fed the diet containing 12% SDEW and pigs fed the diet containing 6% TP-SDEW. There was no change observed in plasma F2-isoprostanes (ISP; P = 0.97) or 8-hydroxy-2-deoxyguanosine (8-OH-2dG; P = 0.28) among pigs fed the dietary treatments. In contrast, a decrease in liver tissue PC concentration (P = 0.04) was observed in pigs fed 12% TP-SDEW when compared to pigs fed 6% and 0% TP-SDEW. There was no impact of inclusion of TP-SDEW on liver ISP or liver 8-OH-2dG (P = 0.80). These results indicate that feeding thermally processed SDEW, increases N and S digestibility and plasma PC, while diminishing liver PC.
The second objective investigated feeding varied levels of DON with or without a mitigation strategy and its impact on growth performance, intestinal integrity, and oxidative stress biomarkers in nursery pigs in a feeding study (CH 3) using 105, mixed sex pigs (initial BW 5.5 kg) which were randomly allotted to 35 pens with 3 pigs per pen, being fed their respective dietary treatments for 45 d. Dietary treatments were factorially arranged with one factor being the inclusion of MTX, low (L-MTX; < 1 ppm) or high (H-MTX; > 2.5 ppm), and the second factor being no mitigation strategy or the inclusion of a mitigation strategy (Biofix Plus, BPL; 1.5 mg/kg diet). There was no interaction between MXT level and BPL on pig performance (P > 0.05). Feeding H-MTX diet decreased ADG, ADFI, and GF (P < 0.05) while the addition of BPL had no effect on growth performance (P > 0.05). An interaction was detected between MTX level and BPL addition on plasma PC, a measure of protein oxidation, where the inclusion of BPL decreased the effect of H-MTX on PC to a greater degree whan when included in the L-MTX diet (P < 0.01). No dietary treatment effects, MTX level of presence of a mitigation strategy, were detected on lipid or DNA damage as measured by thiobarbituic acid reactive substances and 8-OH-2dG (P > 0.10). No differences were observed in plasma lactulose and mannitol ratio as a measure of intestinal permeability across dietary treatments (P > 0.10). Although feeding H-MTX decreased ADG, ADFI and GF, there were minimal effects of H-MTX on oxidative stress measures, with mitigation of oxidation occurring with the inclusion of BPL.
The third objective was investigated (CH 4) in a feeding trial where 64 pigs (32 gilts and 32 barrows, 21 d post wean, 10 kg initial BW) were assigned to one of eight treatments in a 2×2×2 factorial arrangement. The first factor was the lack of or inclusion of 15-A-DON (3 mg/kg diet), the second factor was the inclusion of 7.5% fresh soy oil (SO) or PSO (heated to 135°C for 42 h with air bubbled in at 30 L/min), and the third factor was the inclusion of 10% SDEW or TP-SDEW (100°C for 120 h in a forced air oven). Pigs were fed a common diet for 21 d consisting of 14 d in group pen housing and 7 d adapting to individual pens. On d 21 post weaning, pigs were placed on trial for 28 d with the collection of growth performance. On d 21, blood was collected, and plasma obtained to determine oxidative stress biomarkers as measured by protein, lipid, and DNA damage, and plasma vitamin E (Vit E) status. On d 28, each of the 64 pigs were harvested for the collection of liver tissue and weight, and ileum tissue for analysis and cross section for morphology measures. Feces were collected on d 26 of the trial to determine ATTD of GE, N, and S. No 3-way and only two 2-way interactions were observed across all parameters measured. Feeding pigs diets containing 7.5% PSO reduced ADG, ADFI, and GF (P < 0.01). Feeding pigs diets containing TP-SDEW increased ADG and GF (P < 0.05), but not ADFI (P > 0.10). Feeding pigs diets containing 15-A-DON had no effect on growth performance (P > 0.10). In general, there were minimal impacts of dietary treatments on oxidative stress biomarkers. Pigs fed diets containing 7.5% PSO resulted in an increase in DNA damage as measure by 8-OH-2dG (P < 0.05) and a decrease in circulating Vit E (P < 0.01). In contrast, no effects were observed on protein or lipid damage as measured by PC and ISP in plasma, liver, or ileal tissues, respectively. Relative to general oxidative status as measured by derivatives of reactive oxygen metabolites (ROM), oxy-adsorbent molecules (AXC), and the ratio of ROM to AXC, also known as the oxidative stress index, no dietary treatment differences were observed (OSi; P > 0.10). Inclusion of TP-SDEW and 15-A-DON to the diet did not affect the oxidative stress biomarkers of 8-OH-2dG, PC, ISP, ROM, AXC, OSi or Vit E (P > 0.10) in plasma or liver and ileal tissues. No differences due to dietary treatment were observed on intestinal morphology as measured by villus height, crypt depth, and villus to crypt ratio (P > 0.10). The inclusion of PSO resulted in a decrease of ATTD of GE, N, and S (P < 0.01). The inclusion of 15-A-DON elicited an increase in N digestibility, but the inclusion of TP-SDEW had no effect. These data suggest enteric inducers of oxidative stress have inconsistent responses to specific and general oxidative stress biomarkers, and that a single biomarker cannot be specifically linked to a specific enteric challenge. This lack of consistency could be contributed to individual pig antioxidant capacity, the actual induction (or lack thereof) of an enteric oxidative challenge, or any potential interactive relationship of the pig due to other challenges (e.g., environmental stress, social stress, or disease stress) in addition to the consumption of enteric oxidants as studied herein.
In summary, this thesis reports that enteric challenges have inconsistent responses to oxidative stress biomarkers, and therefore do not consistently induce oxidative stress. These data support that there is not one measure of oxidative stress to predict oxidative status in pigs.
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