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SYMPOSIA: Metabolic and Cardiovascular Diseases in Poultry: Nutritional and Physiological Aspects |
Department of Animal Sciences, Oregon State University, Corvallis, 97331-6702
2 Corresponding author: Gita.cherian{at}oregonstate.edu
| ABSTRACT |
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-linolenic (18:3 n-3) acids are essential fatty acids and are the precursors of long-chain n-6 and n-3 fatty acids such as arachidonic and eicosapentaenoic acids (EPA). Ester-linked arachidonic acid and EPA can be mobilized by phospholipase A2 to generate free arachidonic acid and EPA, which can act as substrates for cyclooxygenase and lipooxygenase to produce eicosanoids. Eicosanoids derived from arachidonic acid, prostaglandin E2, thromboxane B2, and leukotriene B4 are proinflammatory and more potent than eicosanoids derived from EPA such as prostaglandin E3, thromboxane B3, and leukotriene B5. Developing dietary strategies in broiler chickens that enhance the n-3 fatty acid content of tissues is also associated with lipid oxidation and muscle product quality. Therefore, alternative strategies for enhancing tissue n-3 fatty acid content without affecting growth and product quality must be devised. The role of maternal (yolk) fatty acids in modulating the long-chain n-3 fatty acid content of tissues and eicosanoid production in chickens fed a diet lacking in long-chain n-3 fatty acids is investigated. Up to d 42 of growth, the cardiac tissues of chicks hatched from hens fed a high n-3 diet retained higher levels of long-chain n-3 fatty acids than those of chicks hatched from hens fed a low n-3 diet. Chicks hatched from hens fed a high n-3 diet produced less proinflammatory eicosanoids than chicks hatched from hens fed a low n-3 diet. Modulating maternal dietary n-3 fatty acids enhances tissue retention of n-3 fatty acids during growth and reduces proinflammatory eicosanoid production in chicks, which could lead to fewer metabolic and inflammatory-related disorders in poultry.
Key Words: metabolic disorder broiler eicosanoid
| INTRODUCTION |
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Lipids and Fatty Acids in Metabolic Disorders
Much of the information available on the role of lipids and growth-related metabolic disorders was derived from experimentally induced birds. Assessing the fatty acid (FA) status of turkeys with furazolidone-induced dilated cardiomyopathy, Lax et al. (1994) reported an increase in arachidonic acid (20:4 n-6) in the cardiac ventricles. Similarly, feeding flax, a rich source of n-3 FA to broiler birds, Walton et al. (1999) reported reduction in right ventricular hypertrophy and blood viscosity in birds exposed to hypobaric conditions. Hypertrophy of the right ventricle is an indication of right ventricular failure and pulmonary hypertension (Julian and Wilson, 1986), and higher whole blood viscosity is associated with greater blood flow resistance.
Information on the lipid and FA composition of broiler birds with other metabolic disorders such as sudden death is very limited because of the lack of consistency in symptoms that allow sudden death identification. In addition, postmortem changes associated with tissue autolysis may affect tissue lipid composition. Riddell and Orr (1980) noted that birds dying from sudden death had an increase in serum total lipids. Similarly, Chung et al. (1993) reported lower phosphatidyl ethanolamine and total phospholipids in the cardiac tissue of sudden death birds than in pen-mate controls. Assessing the cardiac FA status of sudden death birds, Buckley et al. (1987) reported an increase in arachidonic acid in the cardiac lipids of broilers dying from sudden death when compared with control birds of the same age. Similarly, a significant increase in oleic acid along with a decrease in eicosapentaenoic acid (EPA, 20:5 n-3) and total long-chain n-3 FA was observed in sudden death birds compared with pen-mate control birds by Cherian et al. (2005; Figure 1
). The significant alterations in total fat, monounsaturated, long-chain n-6, and n-3 FA reported in these studies point to a role of dietary FA in metabolic disorders of the cardiovascular system. The current review will focus on the role of lipids with emphasis on polyunsaturated FA in poultry diets and their eicosanoid-related metabolic functions.
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Lipids as Sources of Essential n-6 and n-3 FA
Linoleic (18:2 n-6) and
-linolenic (18:3 n-3) acids are essential FA and are the precursors of bioactive long-chain (>20-carbon) n-6 and n-3 FA. The endogenous formation of arachidonic acid (20:4 n-6) and EPA (20:5 n-3) from linoleic and
-linolenic acid occurs through desaturation and subsequent chain elongation. Arachidonic acid, EPA, and docosahexaenoic acid (DHA, 22:6 n-3) are the major long-chain n-6 and n-3 FA in broiler tissues and cells. The efficacy of linoleic and
-linolenic acids in synthesizing 20-carbon FA depends on factors such as the concentration of n-6 FA and the ratio of n-6 to n-3 FA. Competitive inhibition of enzymes will occur, depending on which substrate is present in high concentration.
Essential FA as Eicosanoid Precursors
Ester-linked arachidonic acid and EPA in cell membrane phospholipids can be mobilized by phospholipase A2 to generate free arachidonic acid and EPA, which can act as substrates for cyclooxygenase and lipooxygenase to produce prostaglandins and thromboxane or luekotrienes and hydroxyeicosatetraenoic acid. Eicosanoids derived from arachidonic acid, prostaglandin E2 (PGE2), thromboxane B2, and leukotriene B4 (LTB4) are more proinflammatory and have been shown to increase vascular permeability, vasodilation, edema, release of lysosomal enzymes, generation of reactive oxygen species, and production of inflammatory cytokines (Calder, 2006). Eicosanoids derived from EPA, prostaglandin E3, thromboxane B3, and leukotriene B5 (LTB5) are less inflammatory and are less potent than n-6 derived eicosanoids. In addition, recent studies have identified a novel group of mediators, E-series of resolvins and docosatrienes formed from long-chain n-3 FA, that appear to exert antiinflammatory effects (Serhan and Arita, 2004).
Dietary Lipids: Effect on Tissue Eicosanoid Precursors
Chickens are monogastric animals, so lipids are absorbed and deposited in tissues mainly in the form in which they are ingested. Therefore, the FA composition of chicken tissues can be influenced readily by dietary FA. When fed a typical commercial diet, arachidonic acid is usually the dominant substrate available for eicosanoid synthesis, hence the predominant bioactive FA in broiler tissues. For example, cardiac lipids of broiler birds fed a commercial broiler diet contain 12 to 15% of FA as arachidonic acid. When sunflower oil (high n-6) or fish oil (high n-3) was included in the diet at 5%, arachidonic acid constituted 31% of cardiac phosphatidyl ethanolamine compared with 23% in fish oil-fed birds. The EPA constituted 10.1% of cardiac phosphatidyl ethanolamine of fish oil-fed birds compared with 0% in sunflower oil-fed birds (Table 2
). These results demonstrate that the substrate availability of eicosanoid precursors in cell membrane phospholipids is dependent on dietary n-6 and n-3 FA. The mechanism by which n-6 and n-3 FA can alter membrane lipid composition and thus affect cellular function is shown in Figure 2
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Maternal Dietary Lipids and Progeny FA Metabolism
In oviparous species, the embryo is dependent upon nutrients stored in the egg for sustaining its growth and development into a healthy hatchling. Once a fertilized egg is incubated, lipid-rich yolk is the only source of FA available for the developing embryo. During the 21-d incubation period, over 80% of yolk FA are absorbed by the developing chick embryo for energy production and structural membrane synthesis (Noble and Cocchi, 1990; Cherian et al., 1997). Therefore, FA available from in ovo sources will affect FA composition of chick tissue cell membranes during growth and development.
Tissue FA in Progeny: Effects of Pre- and Posthatch Diets
Two experiments were conducted to investigate the effects of maternal (prehatch) and posthatch diets on FA changes in the progeny. In the first experiment, breeder hens were fed diets with high, low, or no n-3 FA. The hatched chicks from all 3 treatments were fed the same commercial diet lacking in long-chain n-3 FA but containing 3%
-linolenic acid. Chicks hatched from breeder hens fed the high n-3 diet retained higher levels of long-chain n-3 FA in cardiac and hepatic tissues when compared with chicks hatched from hens fed the low or no n-3 diets (Cherian and Goeger, 2005). A significant increase in the retention of DHA (22:6 n-3) up to d 42 of growth was observed in the cardiac tissue of chicks hatched from hens fed high n-3 diets (Figure 3
). Arachidonic acid (20:4 n-6) concentration was higher up to 14 d posthatch in chicks from hens fed the low n-3 than those from hens fed the high n-3 diet.
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| CONCLUSIONS |
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| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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Received for publication October 27, 2006. Accepted for publication November 19, 2006.
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