Oxidative stress - a key indicator in animal stress

Wednesday, March 24, 2021


Oxidative stress - a key indicator in animal stress


Anja Keiner, Global Technical Manger Swine & Poultry – Delacon Biotechnik


 

Animals experience many situations of stress in their natural environment. This stress can be caused, amongst others, by conflict with group members, water and food shortages, injuries and challenging weather conditions or parasite densities. The term "stress" is widely used to describe a set of physiological and behavioral changes. Factors that trigger stress, so-called stressors, initiate these changes to cope with the challenges.

 

Oxidative stress can be caused by different factors, originating from those mentioned above nutritional, environmental, or internal stress conditions. The stress itself and the animals' stress response include mechanisms that may negatively affect the animals' performance. Among others, immune function impairs, and susceptibility to diseases increases. Also, feed intake and rumination decrease and directly harms performance.


Oxidative stress – what is it?


Metabolic processes in cells require oxidative reactions. During these standard processes, reactive oxygen species (ROS) are produced. ROS are essential metabolites involved in enzymatic reactions, mitochondrial electron transport, signal transduction, activation of nuclear transcription factors, and gene expression. However, due to their reactive nature, ROS can have adverse effects and damage cell walls.


ROS can be neutralized by endogenous antioxidant mechanisms and radical scavengers like polyphenols. In a balanced system, there are enough antioxidants to neutralize ROS. As soon as this system is not balanced anymore and there are more ROS than available antioxidants, oxidative stress is marked mostly due to increased oxidative processes and ROS production.  This leads to cell and tissue damage (e.g., liver cells, mucosal cells).


Oxidative stress in poultry and swine


The gut is one of the most important organs that affect animal performance and health. To support animals during challenging conditions, including oxidative stress, nutrition and management focus on a short gut development after hatching or weaning and maintaining a healthy and intact gut. Maintaining intestinal barrier functions is essential for preventing pathogens from passing the intestinal barrier, the first defense line. Reactive oxygen species from lipid peroxidation in the enterocytes cause a significant reduction of barrier function and reduce gut health overall. Moreover, it affects nutrient uptake and cell turnover.


Lipid and protein oxidation have been recognized to have an enormous impact on membrane stability and meat quality. A pro-oxidative environment initiated before (e.g., stress before slaughter) and after animal slaughter leads to increased oxidative reactions during handling, processing, and storage of poultry meat. This negatively affects meat quality parameters like postmortem pH decline, drip loss, or juiciness.


How to counteract oxidative stress?


Several nutritional strategies are available to alleviate oxidative stress and enhance animals' health and welfare status. The physical form of the diet, feed composition, and quality of single feed ingredients used are primary tools to control and improve performance and health.


Adding synthetic or natural antioxidants to diets, limiting lipid peroxidation in feed is common practice, especially in high dietary levels of polyunsaturated fatty acids (PUFAs). Supporting the animal's antioxidant system by adding selenium, manganese, or Vitamin C or E is well-recognized. However, evidence on the beneficial effects due to the application of natural phytogenic additives as antioxidants is increasing. This is something we have known about human nutrition for years. Diets rich in vegetables and fruits have increased antioxidants' intake and thereby reduce oxidative stress and inflammation, thus minimizing the risk of developing cardiovascular diseases.


Phytogenic feed additives (PFA) contain various biologically active substances like essential oils, flavonoids, pungent and bitter substances, tannins, and saponins and represent a natural and innovative solution to today's challenges in livestock production. Phytogenic feed additives show clear potential to reduce oxidative stress. Recent literature and research data indicate a higher efficacy of such natural antioxidants than the customarily used synthetic antioxidants or vitamin E.

 

There are two different modes of action described for the anti-oxidative effect of PFA, especially for essential oils. Depending on the molecular structure, essential oils can scavenge reactive oxygen species and thereby neutralize them. Secondly, essential oils can support the endogenous antioxidant system by increasing the production of antioxidant enzymes. Superoxidase dismutase (SOD) and Glutathione peroxidase (GSH-PX) are necessary antioxidant enzymes that inactivate harmful ROS. A study on broilers has shown that the addition of a specific PFA, Biostrong® 510, stimulates the synthesis of these enzymes, thereby supporting the endogenous antioxidant system (Figure 1).
 


Additional to the effects on antioxidant enzymes, essential oils with phenolic structures can scavenge ROS, reducing the risk of some diseases like cardiovascular disease, liver dysfunction, and immune system decline directly. With an increasing number of phenolic structures in essential oils, the antioxidant capacity increases. Examples of essential oils with a high content of phenolic structures are thymol, carvacrol, eugenol, and cinnamaldehyde.


As a result of less oxidative stress in the intestine, it showed that the addition of a specific phytogenic combination, Fresta® Protect, improves intestinal integrity in piglets after weaning as indicated in Figure 2.
 


Conclusion


Oxidative stress is not associated with a disease but can result in performance losses and higher susceptibility of animals to diseases. This results in an economic impact on livestock production. Recently, much attention has been paid to nutritional strategies to counteract oxidative stress. One promising way is the supplementation with phytogenic feed additives, as these active substances have shown immense potential for their anti-oxidative properties and efficacy.

 


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Article made possible through the contribution of Anja Keiner and Delacon Biotechnik