Dr. Jayanti L. Agashe1 and Dr. Satish J. Manwar 2
1PhD Scholar, ICAR-CARI, Izatnagar
2Professor & Head, Dept. of Poultry Science, PGIVAS, Akola
Among several dietary components, antioxidants have a special place being major players in the battle for survivability, maintenance, health, productive and reproductive performance of animals. This is largely because of the detrimental effects of free radicals and toxic products of their metabolism on various metabolic processes. Antioxidant balance in the body is responsible for maintaining human and animal health, productive and reproductive performances of farm animals. The antioxidant balance can be adversely modulated by sub-optimal diets and nutrient intakes or positively affected by dietary supplementation. Antioxidants are the chemical compounds which can delay the start or slow the rate of lipid oxidation reaction in different biological systems are known as antioxidant compounds (Emad et al., 2013). These are the molecules that prevent cellular damage caused by oxidation of other molecules (Surai et al., 2002). This oxidation is a chemical reaction that transfers electrons from one molecule to an oxidizing agent. Oxidation reactions are known to produce free radicals. Free radicals are atoms, molecules or any compounds containing one or more unpaired electrons. Most biologically-relevant free radicals are derived from oxygen and nitrogen. That so called reactive oxygen species (ROS) and reactive nitrogen species (RNS). There are two types of ROS; those of free radicals are highly unstable, very reactive and contain one or more unpaired electron(s) in their outer molecular orbit such as superoxide, nitric oxide and hydroxyl radicals, and non-radical ROS, which do not have unpaired electron(s) but are chemically reactive and can be converted to radical ROS such as hydrogen peroxide, ozone, peroxynitrate and hydroxide (Trachootham et al., 2009).The most important effect of free radicals on the cellular metabolism is due to their participation in lipid peroxidation reactions and capable of damaging molecules such as DNA is associated with mutations, translation errors, and disruption of protein synthesis Damage to proteins causes modifications in ion transport and receptor functions, as well as altered enzymatic activities. Polyunsaturated fatty acid oxidation alters membrane composition, structure and properties (fluidity, permeability, etc) and activity of membrane-bound enzymes. The damage to biological molecules ultimately compromises growth, development, immunocompetence and reproduction (Surai et al., 2002).
Antioxidant prevents damages to biologically relevant molecules including DNA, proteins and lipids (Surai, 2014). Increased antioxidant supplementation for improvement of meat quality during storage (Surai et al., 2003).Vitamin E and selenium combination is very effective to reduce drip loss. (Edens, 1997). Decline in egg production due to heat related stress is increase due to less vitamin E in feed. Increase antioxidant. Supplementation decreased mycotoxin toxicity. Provide excellent support for the body immune system (Surai, 2002).
Antioxidants can be classified into two major types based on their source, i.e., natural and synthetic antioxidants
1) Natural Antioxidants – Natural antioxidants either are synthesized in animal body through metabolic process or are supplemented from other natural sources, and their activity very much depends upon their physical and chemical properties and mechanism of action. This can be further divided into two categories, i.e., enzymatic antioxidants and non enzymatic antioxidants.
A) Enzymatic Antioxidants: – these are uniquely produced in the animal body and can be subdivided into primary and secondary antioxidant.
a) Primary Antioxidants
Primary antioxidants mainly include superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx).
b) Secondary Antioxidant
Secondary antioxidant includes glutathione reductase (GR) and glucose-6-phosphate dehydrogenase (G6PDH). G6PDH generates NADPH. GR is required to recycle the reduced glutathione (GSH) using secondary enzyme GR and NADPH.
B) Non Enzymatic Antioxidants
They are a class of the antioxidants which are not found in the body naturally but are required to be supplemented for the proper metabolism (Raygani et al., 2007). Some of the known nonenzymatic antioxidants are minerals, vitamins, carotenoids, polyphenols, and other antioxidants.
a) Minerals- They include selenium, copper, iron, zinc, and manganese. They act as cofactors for the enzymatic antioxidants. Vitamins- such as vitamin A, vitamin C, vitamin E, and vitamin B. They cannot be synthesized in our body and hence need to be supplemented in the diet.
b) Carotenoid- Carotenoid consists of β-carotene, lycopene, lutein, and zeaxanthin. Lutein is best known for its role in protection of retina against harmful action of free radicals and also prevents atherosclerosis (Sikora et al., 2008).
c) Polyphenols – Polyphenols is a class of the phytochemicals that possess marked antioxidant activities. These consist of phenolic acids, flavonoids, gingerol, curcumin, etc. (Amit and Priyadarsini, 2011).
d) Other Antioxidants- Transition Metal-Binding Proteins Albumin, ceruloplasmin, hepatoglobin, and transferring and Nonprotein Antioxidants Bilirubin, uric acids, and ubiquinol are nonprotein antioxidants which inhibit the oxidation processes by scavenging free radicals (Papas, 1998).
2) Synthetic antioxidants
Synthetic antioxidants are artificially produced or synthesized using various techniques. Generally, they are polyphenolic compounds mainly that capture the free radicals and stop the chain reactions. BHT, BHA and Ethoxy quinine is the only heterocyclic, N-containing compound reported to be used as antioxidant in the food, especially animal feed improve their solubility in fats and oils and to reduce their toxicity. These synthetic compounds possessing antioxidant activity are commonly used in pharmaceuticals, as preservatives for cosmetics and to stabilize the fat, oil, and lipid in food (Gupta and Sharma, 2006). (Hamid et al., 2010) EDTA When added as an antioxidant prevents oxygen from causing color changes and rancidity. Ethoxyquin is as an antioxidant primarily used to protect carotenoid oxidation in animal feeds during storage. TBHQ is a highly effective diphenolic antioxidant and used as a preservative for unsaturated vegetable oils and many edible animal fats (Emad et al., 2013).
Oxidative stress is defined as the imbalance between prooxidants and antioxidants. Oxidative stress is regarded as one of the most critical stressors in poultry production. When ROS surpasses the ability of the antioxidant system of an organism to remove them, oxidative stress occurs (Surai, 2003). Body is not able to synthesize the enzymes needed to destroy ROS or repair the damage. Oxidative stress damages cell proteins, lipids, and DNA, and reduces energy generation efficacy. Moreover, oxidized molecules can take electrons from other molecules, resulting in a chain reaction. If not controlled, this reaction can cause extensive tissue damage. Oxidative stress can cause losses in the productive performance, as well as losses in both nutritional and organoleptic quality of the products derived from them. Antioxidants in the diet are thought to play a protective role against oxidative damage (Nimalaratne, 2015).
Oxidative damage to poultry farm to fork
The occurrence of oxidative reactions in each of the stages of the food chain, from animal production to food consumption, is manifested in a number of effects. The nature and extent of these consequences depend on the stage between “farm to fork” in which the oxidative damage is caused and the food components affected by the oxidation reactions.. Oxidation processes negative impact of these reactions on animal growth, performance, and food quality. Lipid oxidation has been recognized a major threat to the quality of processed poultry products. The induction of preslaughter stress on broilers by heat exposure leads to muscles with high susceptibility to lipid oxidation, protein carbonylation, and diverse physiological disorders. The feeding diets with high oxidized oil increased lipid oxidation and Protooxidation and reduced the activities of tissue antioxidant defense enzymes. The most important step in preventing oxidative damage and balancing antioxidant defence in the animal body can be to enhance the antioxidant capacity by optimising the dietary intake of antioxidants. the quality of the final product and the behavior of the food upon ingestion in terms digestibility and impact on health depend on a large number of factors, some of them related to the farming background (animal feeding, managing, and so on). The fact that livestock and human beings share the same fundamental biology and metabolic pathways supports the belief that animal well-being (reducing oxidative stress by proper managing) may also provide benefits to the final consumer (Estevez, 2015).
Other Possible Stresses in Poultry Production
Delay in collecting chicks from incubator. This puts pressure on antioxidant defence capacity and free radical production and antioxidant protection systems. Transportation from hatchery to farm is another source of stress. For breeding companies where chicken transportation could involve several thousand miles, a very high degree of stress should be associated with temperature fluctuation and dehydration and sub-optimal temperatures in the poultry house. Cold tolerance as well as feather cover is influenced by thyroid hormone activity, which is Se-dependent. High levels of ammonia and CO2 in poultry house as a result of inadequate ventilation can substantially decrease antioxidant system efficiency.
Phagocytic immune cells themselves produce free radicals in the process of killing internalised pathogens. Se is considered to have a specific role in immune system regulation, which could be independent on its antioxidant functions.Vaccination is a substantial stress; and in some cases using vitamin E as a vaccine adjuvant can help improve vaccination efficiency. Induced molting with feed withdrawal is an important stress condition when decreased efficiency of heterophil function increases bird susceptibility to various infections. Mycotoxins in the feed can decrease antioxidant assimilation from the feed and increase their requirement to prevent damaging effects of free radicals and toxic products of mycotoxin metabolites (Surai et al., 2002; 2006; 2007).
Oxidative rancidity in feed
Lower palatability of feed. Reduced availability of nutrients.Rancidity may cause destruction of vit A, D, E and several B-complex vitamins.Affects protein value.Imparting off flavour to feed. Reduced pigmentation of broiler skin and yolk (Waheed et al., 2004).
Challenge to maintain the feed quality
When a chicken diet includes fat, which has undergone high temperature treatment, resulting peroxides can contribute substantially to oxidative stress. (Surai et al., 2014). Lipid oxidation is a major problem in the storage of fatty foods affecting its quality and safety (Surai et al., 2010). Changes in lipid oxidation processes especially enhanced during high-temperature treatment. Oxidation changes of lipids lead to the loss of lipophilic vitamins (A, D, E, K), essential fatty acids (linoleic, linolenic, arachidonic) and other biologically active substances. These effects will be reflected in depressed feed performance, with reduced animal weight gain, poor feed conversion, increased disease susceptibility, and greater mortality (Andrews, 2004).Vitamin E and Vitamin C are usually part of natural food items and considered as well known, effective antioxidants (Finley et al., 2011).
Oxidative damage to meat quality
Poultry meat usually becomes unusable during storage for two main reasons: deterioration of the chemical composition or growth of the microbial population. Lipids are an important component of meat and contribute to desirable sensory characteristics of meat. Lipids enhance the flavour and aroma profile of meat and increase tenderness and juiciness. However, it is generally accepted that lipid oxidation is the primary process responsible for quality deterioration of meat during storage. Many plant extracts act as powerful antioxidants in the alteration of chicken meat quality and safety; lowering cholesterol and decreasing lipid-oxidation processes (Weber et al., 2001)
Recently a new concept of how vita-genes regulate the adaptive ability of humans and animals to various stresses has been developed. There is a range of genes responsible for the synthesis of various antioxidant compounds (heat shock proteins, antioxidant enzymes, sirtuins, etc.) and that there are nutrients which can affect expression of such genes. Carnitine, betaine, vitamin E and some other elements are proven to be effective regulators of vita-genes. Based on the aforementioned positive effects of dietary antioxidants on protection against various stresses in poultry production, a range of anti-stress compositions/premixes have been developed. However, in stress conditions feed consumption is substantially decreased so the effects of feed supplements are also decreased. The new concept was based on an idea that supplying birds with various antioxidants via the water could help them to deal with stress conditions more effectively. Indeed, it was proven that inclusion of vita-gene-regulating compounds in water, as well as some minerals, vitamins, electrolytes and organic acids could be effective in fighting various stresses (Fotina et al., 2011; Fotina et al., 2014).
How antioxidants act?
Biological antioxidants react with free radicals or precursor metabolites converting them into less reactive molecules and preventing or delaying oxidation of biological molecules. The most important and well-characterised natural antioxidants in the animal body are vitamins E and C. When the antioxidant system finds itself in high stress conditions, if free radical production is increased dramatically, then without external help there will be difficult to prevent damage to organs and cells. Such external help can be provided by dietary supplementation with increased doses of natural antioxidants, especially minerals such as selenium. For nutritionists or feed formulators it is a great challenge to understand when the antioxidant team in the animal body requires help and how much of this help can justify extra feed expense, because antioxidants are typically expensive components of the diet. A list of possible stresses in poultry production includes the following (Surai, 2007).
Commonly occurred Natural Antioxidants in poultry
All the living organisms have specific antioxidant defense mechanism to deal with ROS (Halliwell and Gutteridge, 1999). They are natural antioxidants which make them possible to survive in oxygen rich environment (Halliwell, 1991). This mechanism is generally known as antioxidant system and includes natural antioxidant vitamins. It is diverse and responsible for the production of cells from the action of free radicals. This system includes Natural fat-soluble antioxidant (vitamins A, E, carotenoids, ubiquinones, etc.); water-soluble antioxidant (ascorbic acid, uric acid, taurine, cartinitine etc.); antioxidant enzymes: GSH-Px, CAT and SOD; thiol redox system consisting of the glutathione system (glutathione/glutathione reductase/glutaredoxin/glutathione peroxidase and a thioredoxin system (thioredoxin/thioredoxin peroxidase/thioredoxin reductase). The protective antioxidant compounds are located in organelles, subcellular compartments or the extracellular space enabling maximum cellular protection to occur. Thus antioxidant system of living cell consists of three major levels of defense (Surai, 1999) and the first step is responsible for prevention of radical formation by removing precursors of free radicals or by inactivating catalysts. The second level of defense is to prevent and restrict chain formation and propagation and which consist of chain breaking antioxidant like vitamin E. The chain breaking antioxidant inhibits peroxidation by keeping the chain length of propagation reaction as small as possible (Surai, 2003). The third level of defense is excision and repair of damaged parts of molecules which include lipolytic (lipases), proteolytic (peptidases or proteases) and other enzymes (DNA repair enzymes, polymerase, ligases, phospholipases, nucleases. The antioxidant compounds are located in organelles, subcellular compartments or the extracellular providing maximum cellular protection (Panda et al., 2014).
Commonly used synthetic antioxidants in poultry production
During storage of animal feed many different processes may occur which alter their initial natural proprieties. First of all, lipids undergo peroxidation, the process during which they are deteriorated in a free radical autocatalytic oxidation chain reaction with atmospheric oxygen. Therefore synthetic antioxidants are widely used, among which BHT (butylated hydroxytoluene), BHA (butylated hydroxyanisole), and EQ (ethoxyquin) are the most frequent.
Ethoxyquin (EQ, 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline) is widely used in animal feed in order to protect it against lipid peroxidation. Ethoxyquin is also known as Santoquin, Santoflex, Quinol. EQ cannot be used in any food for human consumption (except spices, e.g., chili), but it can pass from feed to farmed fish, poultry, and eggs, so human beings can be exposed to this antioxidant. Its unquestionable advantage is its high antioxidant capacity and low production costs. Specifically it is used to retard oxidation of carotene, xanthophylls, and vitamins (like vitamins A or E). Ethoxyquin has been used as an antioxidant in animal feed for several decades and despite the search for new compounds that could be used as free radical scavengers, it is still the most effective antioxidant. The level of this antioxidant in animal feeds should not be higher than 150 ppm (U.S. Food and Drug Administration permissions) (Alina, 2013).
BHA (butylated hydroxyanisole) It is a monophenolic, lipid-soluble antioxidant, better used for the lipid oxidation in animal fat compared to vegetable oil. Dose should not exceed 0.02% fat or oil content. Retards the oxidation of Vitamin A, Fats, and Vegetable Oils. BHT (butylated hydroxytoluene):- It is also a monophenolic fat-soluble antioxidant but is more stable than BHA at high temperature, and both act synergistically. BHT is widely used to prevent oxidation in oils. Food and Drug Administration allows up to 0.01% in poultry by fat content Many commercially available antioxidant formulations contain both of these antioxidants.
Reviews on Antioxidants
1) On evaluation of effect of Ethoxyquin at various level of oil % in feed stored on the quality of broiler rations stored at high temperature, it was concluded that Santoquin level improved the stability of fat in feeds stored at high temperature (Waheed et al., 2004).
2) On evaluate the effect of vitamin c, vitamin E, zinc and chromium against the deleterious impacts of heat stress on broilers. The results revealed that supplementation of antioxidants improved the viability and decreased the mortality to the degree that no deaths occurred in the vitamin group and in the other groups the rate was less than that in the heat stressed control (Tawfeek et al., 2014).
3) Effect of Antioxidants vitamin E and selenium (E-care Se) on performance of broilers.
It was concluded from the results of the study that antioxidants (vitamin E and Se) may be used with basal diet to get best result in terms of body weight gain, The better performance might be due to the synergistic action of both of them on the physiological system of the birds. (Biswas et al., 2011)
4) Comparative effect of antioxidants
Experiments was assessing the efficiency of natural antioxidants rosemary (ROS), small red bean (SRB), sunflower seeds (SFS) and ginger (GGR) extracts compared to the synthetic antioxidant (BHT) on characteristics of chicken meat were studied. The results suggest that natural antioxidants may have the ability to inhibit the lipid oxidation and enhance meat quality. The impact of natural antioxidants was similar to that of BHT (Khurshid, 2015).
Limitations of natural antioxidants
If natural antioxidant not purified properly are less efficient. They are more expensive if purified. May impart colour, taste, or off-flavours to the product. They are less stable-Extremes of temperature and pH affect their stability. They themselves are susceptible for oxidation – Some of the natural antioxidant like tocopherols is susceptible for oxidation because of their nature (Pashtetsky, 2019).
Limitation on usage of synthetic antioxidants
Antioxidants that are used in feeds must be extensively tested e.g. for the absence of carcinogenicity and other toxic effects in the antioxidant itself. Beneficial if added at concentrations permitted by legislation. Higher dosage of antioxidants may leads to residual and cause adverse effect to consumer.Synthetic antioxidant show carcinogenic activity in human when use in higher dosage. (Alina, 2013).
Antioxidants show a positive effect on the lipid oxidation in chicken meat. Better to use natural antioxidants instead of synthetic one. Antioxidant defense system is always maintained in the body to counter the adverse effect of oxidative stress developed in the biological system due to the formation of reactive oxygen species. vitamin E is major membrane antioxidant, which cannot be replaced by other antioxidants. Provision of minerals necessary for additional synthesis of SOD and GSH-Px (Zn, Mn, Se). The nutrient enriched value added poultry eggs and meat greatly increased the context of functional foods for human health. Vitagene upregulation in stress condition is emerging as an effective means for stress management.
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