Based on many concepts recently published in some important reviews, and some presentations at the Annual Poultry Science Association Symposium in 2017, suggestions to improve the efficiency of dietary antioxidants with polyphenols have been made.
Oxidative stress
Mammals obtain energy by burning food with the breathing of oxygen. It is a complex combination of nutrients digestion, absorption, cells respiration and oxygen metabolism. This is a controlled metabolic process that generates different byproducts formed mainly in the mitochondria cells.
These byproducts are named reactive oxygen species (ROS). The most important ROS are free radicals (mainly oxygen or nitrogen), which are electronically unstable atoms or molecules capable of consuming electrons from any other molecules they meet in an effort to achieve stability – in some cases, affecting or producing damage to the other molecules.
The animal is naturally endowed with an overwhelming biological antioxidant system to combat free radicals continuously produced in the body cells. The total antioxidant status (TAS) is the natural antioxidant capacity of any organism. Like a team working together, it is called the antioxidant defense system.
Based on these concepts (ROS and TAS), there is a balance among the antioxidant defense system and the free radicals’ production. When the system is under control in equilibrium, TAS can manage ROS or free radical production. Table 1 describes the enzymes and nutrients (trace minerals) working for the TAS in the biological systems.
Any situation affecting the bioavailability of these nutrients may affect TAS efficiency.
Oxidative stress develops when free radicals’ generation exceeds TAS or the body antioxidants capacity. Many different situations can affect the equilibrium between TAS and ROS. For example:
Nutritional factors
- High polyunsaturated fatty acids or oil in dietary ingredients during storage
- Dietary oxidation of fatty acids producing aldehydes, ketones and esters that may produce rancid flavor, reducing feed palatability
- Unbalanced diets (For example, excess of vitamin A can reduce the effect of other antioxidants such as vitamin E or carotenoids.)
- Nutrient deficiency and antagonisms between minerals (For example, excess of sulfur in drinking water may affect selenium bioavailability. Selenium is called the “chief executive” of antioxidant defense and its deficiency is considered one of the major causes of oxidative stress.)
Physiological and pathological factors
- Pathogenic infections
- Metabolic disorders such as ascites (abnormal buildup of fluid in the abdomen)
- Toxins: heavy metals, pesticides, fungicides, mycotoxins, etc.
Environment and animal welfare
- Heat stress is a major cause of oxidative stress on animal production in tropical countries, particularly poultry.
- Limited housing space
- Insufficient ventilation
- Social interactions
- Transportation
The natural antioxidant system or TAS is based on three levels of defense. First level: the antioxidant enzymes in the cytosol and mitochondria described in Table 1.
Second level: natural antioxidants. For example, vitamin E performs part of the job detoxifying peroxyl radicals or peroxyl radicals in hydroperoxides, which are still toxic and must be detoxified by selenium-dependent glutathione peroxidase to water (see Table 1). Third level: the reactions of free radicals with biological molecules (DNA, proteins, lipids, etc.) results in oxidative damage of these molecules, also potential cellular damage and, in extreme cases, cell death.
Specific enzymes (e.g., HSP or heat shock protein family) are involved in repairing molecule damage by free radicals. The 2015 Nobel Prize in Chemistry was awarded to Tomas Lindahl, Paul Modrich and Aziz Sancar for their work on the molecular mechanisms of DNA repair processes.
Antioxidant use in livestock
There is an intimate relationship between different animal production stressors, particularly in hot climatic regions like heat stress, oxidative stress, systemic inflammation and immunosuppression. Low, weak or unbalanced TAS has been implicated in several disease states, such as breast muscle anomalies in birds or cancer and heart diseases in humans.
An antioxidant is a molecule that prevents or inhibits the oxidation of other molecules. Antioxidants can be classified in different ways; the simplest classification is:
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Enzymatic: Natural antioxidants can be synthesized in the body through metabolic process or supplemented in the diet from other sources (natural or synthetic).
- Non-enzymatic: Nutrients required by animals (minerals, vitamins, etc.) that are not found naturally in the body (carotenoids, some provitamins, proteins and non-protein nitrogen, natural polyphenols, etc.).
Vitamin E is probably the most important antioxidant used for animal production. Vitamin E has been extensively researched, maintaining cell membrane integrity, prolonging shelf life of muscle, facilitating immune response mechanisms, etc.
However, vitamin E as an antioxidant is part of the coordinated antioxidant system, which includes vitamin C, selenium, manganese, copper, iron and zinc as co-factors for selected antioxidant enzymes (superoxide ismutase, selenium-dependent glutathione peroxidase, catalase, etc.).
It is clear under oxidative stress conditions there is a need of exogenous supplementation of antioxidants. However, some dietary antioxidants could act as pro-oxidants, particularly when supplemented in excess of animal requirements.
Pro-oxidants can induce oxidative stress in biologic systems by increasing the production of reactive free radicals or depleting the antioxidant defense system to cause cellular damage. There is need for in-depth research to ascertain the in vivo relevance of high dosage of antioxidant substances with regard to their potential to exhibit pro-oxidant effects.
The use of antioxidants in livestock will be driven by the impact of modern intensive livestock practices, which simultaneously elevate the exposure of animals to oxidative stress conditions. Nowadays, it is an increasing demand by consumers for the use of natural products in livestock production.
Natural vegetable extracts such as polyphenols is a class of phytochemicals that possess marked antioxidant activities and, at low dosage, may help to improve the antioxidant status of animals.
Two important scientific reviews concluded some phytochemicals, such as various types of polyphenols and tannins, have shown beneficial effects to help control oxidative stress on animals under stress conditions. Indeed, there is a possibility to partially replace the use of costly synthetic vitamin E used over animal requirements with less expensive natural phenolic products.
Final message
- Balance dietary nutrient and antioxidant levels according to animal requirements to avoid pro-oxidative effects.
- Replace the use of costly synthetic vitamin E in excess of animal requirements by blending less expensive polyphenols.
- To balance mineral requirements and to control possible trace mineral deficiencies or antagonisms, analyze mineral content in the diet, including drinking water.
- The efficiency of antioxidants depends on the dose and duration of applications. Use companies with supported research products and enough time in the market that can guarantee a supply of quantity and quality polyphenols.
References omitted but are available upon request. Click here to email an editor.
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Alejandro Castillo
- Farm Adviser – Dairy Science
- University of California Cooperative Extension
- Email Alejandro Castillo
