Omega-3 fatty acid enriched eggs: advantage of chia over other raw materials
Ricardo Ayerza (h)
Office of Arid Lands Studies,
The University of Arizona.
The information in this document is from a paper entitled “Chia as a new source of ω-3 fatty acids: advantage over other raw materials to produce ω-3 enriched eggs” which was presented by R. Ayerza (h) at the Symposium On Omega-3 Fatty Acids, Evolution and Human Health (Washington, D.C., September 23-24, 2002), organized by Belovo S.A.
At present there are ω-3 enriched eggs on the market which are obtained by including flax seeds, chia seeds, fish oil/meal or marine algae in the hens’ diet. The purpose of this paper is to compare chia with the other raw materials.
Of the raw materials used, only flax (Linum usitatissimum L.) and chia (Salvia hispanica L.) are agricultural crops. These are the two vegetal species having the highest concentration of ω-3 α-linolenic fatty acids known to date (Ayerza, 1996, 1995; Coates and Ayerza, 1998,1996; Oomah and Kenasehuk, 1995).
The other two sources of ω-3 fatty acids, algae and fish oil, are of marine origin. Both contain long chain ω-3 fatty acids, DHA and DHA and EPA, respectively (Table 1). Comparing the oil composition of these four sources of ω-3 fatty acids, it can be seen that the terrestrial sources have a much higher ω-3 content, than do the marine sources (Table 2).
Due to easy accessibly of fish oils/meals as a soucre of ω-3 fatty acids, use of various levels in poultry diets have been reported in recent years (Scheideler et.al, 1997; Nash et al., 1996; Nash et al., 1995; Van Elswyk et al., 1995; Marshall et.al, 1994; Van Elswyk et al., 1992 ). However, fish oils are generally by-products obtained during the preparation of fish meal, and as a consequence their composition is not uniform and changes according to the source of the marine oil and degree of hydrogenation. Variations in fatty acid composition according to season, place of harvest, species, etc. are well known, and wide variations in commercial fish oils/meal have been reported. (Valenzuela and Uauy, 1999; Sebedio, 1995; Ackman, 1992). For example, menhaden fish oil and cod liver oil have approximatelly equivalent EPA levels (10%), whereas 20% of sardine fish oil fatty acids is EPA (Alexander et al., 1995).
Fish liver oils such as cod liver oil have higher vitamin A levels than do fish oils that are whole-body products. Increased dietary vitamin A has been shown to antagonize vitamin E status in poultry and other animals (MacGuire et al., 1997; Abawi and Sullivan, 1989; Tengerdy and Brown, 1977).
Reproductively active hens have exhibited increased hepatic lipidosis following six months of feeding 3% menhaden fish oil. Van Elswyk et al. (1994) suggested that dietary menhaden oil enhances the lipogenic activity of the liver in laying hens.
Owing to the availability of flax (as industrial oil) and due to its relatively low price, there have been many attempts to use it as an ω-3 fatty acid source in poultry production, though not very successfully. Numerous scientific publications have shown the negative effects that the antinutritional factors of flax have on the development of layers and broilers (Treviño et al., 2000; Novak and Scheideler, 1998; Bond et al., 1997; Ajuyah et al., 1993; Bhatty, 1993; Lee et al., 1991; Bell, 1989; Homer and Schaible, 1980; Kung and Kummerow, 1950). Thus, in order to use flax in poultry diets, the seeds have to be detoxified. The most efficient processes require the utilization of solvents, and even then the seeds cannot be completely detoxified (Mazza and Oomah, 1995; Madhusudhan et al., 1986).
None of the toxic factors found in flax have been found in either chia seeds or chia oil (Ayerza and Coates, 2002, 2001, 2000, and 1999; Ayerza et al., 2002; Lin et al., 1994; Weber et al., 1991; Ting et al., 1990, Bushway et al., 1984).
Considering the α-linolenic fatty acid content of flax and chia (Table 1) and the rate of incorporation of ω-3 fatty acids in eggs that each brings about, chia has proven to have a higher efficiency, by almost 230%, compared to flax (Table 5). This difference could be related to the different antioxidant compounds found in flax and chia and their influence on fatty acid incorporation. Ajuyah et al. (1993), observed that including antioxidants in broiler diets containing flax caused a significant increase in ω-3 fatty acid incorporation into broiler white meat, however adding antioxidants did not affect the decrease in body growth observed.
The higher fatty acid deposition efficiency shown by chia, compared with flax, could also be related to the digestion process of the lipids. Numerous factors are capable of causing variations in intestinal absorption and tissue deposition of fat and fatty acids in non-ruminants.
Eggs laid by hens fed flax seeds have a characteristic (unpleasant) smell, similar to that of hens fed fish oil(Van Elswyk et al., 1995; Caston et al., 1994; Jiang et al., 1992; Van Elswyk et al., 1992; Adam et al., 1989; Koeheler and Bearse, 1975). In a study made in the USA in five cities, it was shown that consumers generally are reluctant to eat eggs smelling/tasting of fish (Marshall et al., 1994). The absence of atypical organoleptic characteristics in the eggs laid by hens fed chia, represents a significant comparative advantage for this grain, compared to flax and fishing by-products (Ayerza and Coates, 2002, 2001, and 1999).
The difference in organoleptic characteristics of eggs produced with flax and chia can be attributed to the powerful action of chia antioxidants which are absent in flax (Shukla et al., 1996; Intemational FloraTechnologies, 1990; Taga et al., 1984) and/or to the interaction between the other components in flax and the hen’s physiology (Marshall et al., 1994). In the case of fish oil, the typical smell is due to the greater instability of DHA and EPA as compared to α-linolenic acid, combined with the absence of antioxidants capable of preventing them from undergoing this degenerative process (Shukla and Perkins, 1998).
In case of marine algae, available commercial information has reported the absence of fish smell or taste in the eggs produced. However, it has not been possible to locate any scientific papers supporting this claim. An indirect reference about off-flavors in eggs from hens fed algae-enriched diets can be found in a non-scientific paper by Abril et al. (2000). They mention that including up to 1% algae in the diet of laying hens did not produce a significant decrease in overall egg acceptability in terms of aroma and/or flavor. Although there is no scientific information available for or against this, the high content of DHA combined with the instability of DHA in the presence of oxygen, would indicate a strong possibility to transmit undesirable organoleptic characteristics to eggs produced with high amounts of algae in the diet.
In summary, several studies provide solid evidence that including more than 5% flax seed, 1.5% fish oil or 1% algae in laying hen’s diets will result in a significant decrease of overall egg acceptability in terms of aroma and/or flavor. However it is possible to include up to 30% chia in a hen’s diet, without encountering negative consumer preferences as compared to common eggs. This means a maximum potential enrichment of T-3 fatty acids of 175 mg/egg for algae, 207 mg/egg for fish oil, 214 mg/egg for flaxseed, and 986 mg/egg for chia seed, without affecting egg organoleptic characteristics (Ayamond and Van Elswyk, 1995; Van Elswyk et al., 1995; Abril et al., 2000; Ayerza and Coates, 2002, and 2000).
Chia, used as an ω-3 source, eliminates the need to add antioxidants such as vitamins to the hen’s diet. Another factor to consider is that vitamin E has been demonstrated to promote oxidation when an upper level is passed. Low and high limits for oxidation effectiveness are very close to one another, making it very difficult to add a correct amount when mixing the ingredients in animal feeds (Leeson et al., 1998).
One advantage of consumption by hens of α-linolenic fatty acids from plants sources over ω-3 fatty acids from fish/algae sources is that the problem of insufficient antioxidant intake does not exist with higher intakes of α-linolenic fatty acids from plant sources (Simopoulos, 1999).
Egg yolks from laying hens fed chia-enriched diets show a significant increase not only in α-linolenic fatty acid, but also in DHA. As in humans, poultry have shown the capacity to increase DHA by desaturation and elongation of α-linolenic fatty acid in the liver (Table 2). Eggs from hens fed 7% and 14% chia diets had α-linolenic:DHA ratios of 1.8 and 3.1, respectively (Table 3).
Eggs from hens fed chia have a relationship between α-linolenic essential fatty acid and its metabolite DHA, similar to that found in human milk in Germany, France, Nigeria, Japan and China. Also the DHA:α-linolenic ratios in the eggs produced by hens fed 7% chia diets are similar to the eggs produced by hens fed under free ranging conditions, that is hens consuming green leafy vegetables, fresh and dried fruits, insects and the occasional worm (Simopoulos and Salem, 1992).
The reduction in total saturated fatty acids in general, and especially in palmitic (up 30.6%) fatty acid in the eggs produced by hens fed chia-enriched diets, indicates an additional health advantage for these omega-3-enriched eggs. Recent research suggests that the reduced saturated fatty acid content in the egg yolk is feed dependent. This gives chia a dramatic advantage compared with fish and algae products which are very high in palmitic saturated fatty acid (Ayerza and Coates, 2000).
Omega-3 levels in commercial eggs
Table 4 shows examples of ω-3 eggs which are available in Argentina, Brazil, Canada, Spain and USA. The Mega-3 egg which is obtained by including 14% chia in the diet of layers contains one of the highest ω-3 levels (1120 mg/gr. of yolk) of all commercially available eggs Table 4. However, the Mega-3 egg level is far below the enriching potential which has been shown possible for chia (Table 7). This is also possible without causing problems in the body development of hens, in the production of eggs, or with the flavor, smell or texture of the eggs (Ayerza and Coates, 2001, 2000, and 1999; Neely, 1999).
To date there is little published literature comparing chia to other sources of ω-3 fatty acids when used in the same experiment. However, recent unpublished papers show the advantage of chia over diets containg fish oil and flax in the production of ω-3 eggs (Tables 5, 6 and 9). One recently published study (Ayerza and Coates, 2001), reports the negative effects of flax in term of egg production when incorporated in a chia enriched diet for laying hens (Table 8).
Considering the α-linolenic fatty acid content of flax and chia (Table 1) and the incorporation of ω-3 fatty acids in eggs it can produce, chia provides a higher efficiency (by almost 230%) over flax (Table 5). This difference could be related to the different antioxidant compounds found in flax and chia and their influence on fatty acid incorporation. Ajuyah et al. (1993), observed that including antioxidants in broiler diets caused a significant increase in ω-3 fatty acid incorporated into the broiler white meat, however they also observed that the addition of antioxidants did not affect the body growth decrease produced by dietary flaxseed.
Also, the higher fatty acid deposition efficiency shown by chia, compared with flax, could be related to the digestion process of the lipids. Numerous factors are capable of causing variations in intestinal absorption and tissue deposition of fat and fatty acids in non-ruminants. These factors include: saturated:unsaturated fatty acid ratio (Lessire et al., 1996); monounsaturated fatty acid plus polyunsaturated:saturated fatty acid ratio (Chang and Huang, 1998); and total ω-6:ω-3 fatty acid ratio (Wander et al., 1997) in the diet. Digestive utilization of fatty acids varies according to its position on the glycerol molecule, hence, differences between chia and flax α-linolenic fatty acid positions, could explain chia’s higher ω-3 fatty acid incorporation than with flax (Porsgaard, and Høy, 2000; Straarup and Høy, 2000; Innis and Dyer, 1997; Lessire et al., 1996).
Available information suggests that none of the current levels of ω-3 fatty acid incorporation produced by feeding chia could be reached using flax, fish oil or algae based diets without negatively affecting hen performance and/or one or more of the intrinsic characteristics of eggs. In all cases, the limiting factor for utilization of high percentages of available ω-3 sources, with the exception of chia, is flavor, smell and/or atypical textures transmitted by these products to the eggs. Also in the case of flax, animal production would be negatively affected.
* Abawi, F.G., and W. Sullivan. 1989. Interactions of vitamins A, D3, E, and K in the diet of broiler chicks. Poultry Science, 68:1490-1498.
* Abril. J.R., W.R. Barclay, and P.G. Abril. 2000. Safe use of microalgae (DHA GOLD) in laying hen feed for the production of DHA.enriched eggs. Pages 197-202 in Egg Nutrition and Technology edited by J.S. Sim, S. Nakai, and W. Guenter. CAB International 2000, Wallingford, Oxon, U.K.
* Abril, R. and W. Barclay, 1998. Production of docosahexaenoic acid-enriched poultry eggs and meat using an algae-based feed ingredient. Pages 77-88 in A.P. Simopoulos ed. The return of ω3 fatty acids into the food supply. Karger AG., Basel, Switzerland.
* Ackman, R.G. 1992. Fatty acids in fish and shelfish. Pages 169-184 in Fatty acids in food and their health implications, edited by C.K. Chow. Marcel Dekker, Inc., New York, USA.
* Adam, R.L., D.E. Pratt, J.H. Lin and W.J. Stadelman, 1989. Introduction of omega-3 polyunsaturated fatty acid into eggs. Poultry Science, 68 (SPSS Abstracts.):166.
* Ajuyah, A.O., R.T. Hardin, and J.S. Sim. 1993. Effect of dietary full fat flax seed and without antioxidant on the fatty acid composition of major lipid classes of chicken meats. Poultry Science, 72:125-136.
* Alexander, D.W., S.O. McGuire, N.A. Cassity, and K.L. Fritsche. 1995. Fish oils lower rat plasma and hepatic, but not inmune cell α-tocopherol concentration. Journal of Nutrition, 125:2640-2649.
American Heart Association. 1999. Homocysteine, folic acid and cardiovascular disease. Retrieved November 11, 1999 from the World Wide Web, http: //www.americanheart.org/ Heart_ and_Stroke_A_Z_ Guide/ homocys. html
American Hearth Association. 1988. Dietary guidelines for healthy American Adults: A statement for physicians and health professionals. Arteriosclerosis, 8:221A.
* Ayamond, W.M. and M.E. Van Elswyk. 1995. Yolk thiobarbituric acid reactive substances and n-3 fatty acids in response to whole and ground flaxseed. Poultry Science, 74:1388-1394.
* Ayerza, R. (h). 1996. Fatty acid composition, protein and oil content of chia (Salvia hispanica L.) grown in Columbia and Argentina. Third European Symposium on Industrial Crops and Products, Reims, France.
* Ayerza, R. (h). 1995. Oil Content and Fatty Acid Composition of Chia (Salvia hispanica L.) from Five Northwestern Locations in Argentina. Journal of The American Oil Chemists’ Society, 72:1079-1081.
* Ayerza, R. (h) and W. Coates. 2002. Dietary levels of chia: influence on hen weight, egg production, and egg sensory quality. British Poultry Science, Basingstoke, Hants, U.K. (In Press).
* Ayerza, R. (h).and W. Coates. 2001. The omega-3 enriched eggs: the influence of dietary linolenic fatty acid source combination on egg production and composition. Canadian Journal of Animal Science, 81:355-362.
* Ayerza, R. (h) and W. Coates. 2000. Dietary levels of chia:influence on yolk cholesterol, lipid content and fatty acid composition, for two strains of hens. Poultry Science, 78:724-739.
* Ayerza, R. (h), and W. Coates. 1999. An omega-3 fatty acid enriched chia diet: its influence on egg fatty acid composition, cholesterol and oil content. Canadian Journal of Animal Science,79:53-58..
* Ayerza, R. (h), and W. Coates. 1997. An omega-3 fatty acid enriched chia diet: its influence on egg fatty acid composition, cholesterol and oil content. Page 51 in Abstracts of An International Conference of the Association for the Advancement of Industrial Crops, Saltillo, Mexico, September 14-18, 1997.
* Ayerza,R. (h), W. Coates, and M. Lauria. 2002. Chia seed (Salvia hispanica L.) as an ω-3 fatty acid source for broilers: influence on fatty acid composition, cholesterol and fat content of white and dark meat, growth performance and sensory characteristics. Poultry Science (79):724-739.
* Bell, J.M. 1989. Nutritional characteristics and protein uses of oilseed meals. Pages 192-207 in Oil crops of the world, edited by G. Robbelen, R.K. Downey, and A. Ashri. McGraw-Hill Publishing Co., New York, New York, USA .
* Bhatty, R.S. 1993. Further compositional analyses of flax: mucilage, trypsin inhibitors and hydrocyanic acid. Journal of American Oil Chemistś Society, 70(9):899-904.
* Bond, J.M., R.J. Julian, and E.J. Squires. 1997. Effect of dietary flaxseed on broiler growth, erythrocyte deformability and fatty acid composition of erythrocyte membranes. Canadian
Journal of Animal Science, 77:279-286.
* Bushway, A.A., A.M. Wilson, L. Houston, and R.J. Bushway. 1984. Selected properties of the lipid and protein fractions from chia seed. Journal of Food Science, 49:555-557.
* Caston, L.J., E.J. Squires and S. Leeson, 1994. Hen perfomance, egg quality, and the sensory evaluation of eggs from SCWL hens fed dietary flax. Canadian Journal of Animal Science, 74:347-353.
* Chang, N.W. and P.C. Huang. 1998. Effects of the ratio of polyunsaturated and monounsaturated fatty acid to saturated fatty acid on rat plasma and liver lipid concentrations. Lipids, 33(5):481-487.
* Coates, W. and R. Ayerza (h). 1998. Commercial production of chia in Northwestern Argentina. Journal of American Chemists’ Society, 75(10):1417-1420.
* Coates, W. and R. Ayerza (h). 1996. Production potential of chia in Northwestern Argentina. Industrial Crops and Products, 5:229-233.
* Homer, P. and P.J. Schaible. 1980. Poultry: feeds and nutrition. AVI Publishing Co., Inc., Westport, USA.
Hu, F.B., M.J. Stampfer, J.E. Manson, E.B. Rimm, A. Wolk, G.A. Colditz, C.H. Hennekens, and W.C. Willet. 1999. Dietary intake of alpha-linolenic acid and risk of fatal ischemic heart disease among women. American Journal of Clinical Nutrition, 69:890-897.
* Innis, S.M., and R. Dyer. 1997. Dietary triacygycerols with palmitic acid (16:0) in the 2-position increase 16:0 in the 2-position of plasma and chylomicron triacyglycerols, but reduce phospholipid arachidonic and docosahexaenoic acids, and alter cholesteryl ester metabolism in formula-fed piglets. Journal of Nutrition, 127:1311-1319.
* International Flora Technologies, Inc. 1990. Oil of Chia. Apache Junction, USA.
* Jiang, Z., D.U. Ahn, L. Lander and J.S. Sim, 1992. Influence of feeding full-flax and sunflower seeds on internal and sensory qualities of eggs. Poultry Science, 71:378-382.
* Koeheler, H.H., and G.E. Bearse. 1975. Egg flavor quality as affected by fish meals or fish oils in laying rations. Poultry Science, 54:881-889.
* Kung, T.K. and F.A. Kummerow. 1950. The deposition of linolenic acid in chickens fed linseed oil. Poultry Science, 29:846-851.
* Lee, K.H., J.M. Olomu, and J.S. Sim. 1991. Live perfomance, carcass yield, protein, and energy retention of broiler chikens fed canola and flax full-fat seeds and the restored mixtures of meal and oil. Canadian Journal of Animal Science, 71:897-903.
* Lessire, M., Doreau, M., and Aumaitre, A. 1996. Digestive and metabolic utilization of fats in domestic animals. Pages 703–713 in Oils and fats manual, edited by A. Karleskind. Lavoisier Publishing, Paris, France.
* Leeson, S., L. Caston and T. MacLaurin. 1998. Organoleptic evaluation of eggs produced by laying hens fed diets containing graded levels of flaxseed and vitamin E. Poultry Science, 77:1436-1440.
* Lin, K.Y., and J.R. Daniel. 1994. Structure of chia seed polysaccharide exudate.Carbohydrate Polymers (23):13-18.
* Madhusudhan, K.T., H.P. Ramesh, T. Ogawa, K.Sasaoka, and N. Singh. 1986. Detoxification of commercial linseed meal for use in broiler rations. Poultry Science, 65:164:171.
* Marshall, A.C., A.R. Sams, and M.E. Van Elswyk. 1994. Oxidative stability and sensory quality of stored eggs from hens fed 1.5% menhaden oil. Journal of Food Science, 59(3):561-563.
* Mazza, G. and B.D. Oomah. 1995. Flaxseed, dietary fiber, and cyanogens. Pages 56-81 in Flaxseed in Human Nutrition, edited by S.C. Cunnane and L.U. Thompson. American Oil Chemists’ Society Press, Champaign, USA.
* McGuire, S.O., D.W. Alexander, and K.L. Fritsche. 1997. Fish oil source differentially affects rat inmune cell α-tocopherol concentration. Journal of Nutrition, 127:1388-1394.
* Nash, D.M., R.M.G. Hamilton, K.A. Sanford, and H.W. Hulan. 1996. The effect of dietary menhaden meal and storage on the omega-3 fatty acids and sensory attributes of egg yolk in laying hens. Canadian Journal of Animal Sciences, 76:377-383.
* Nash, D.M., R.M.G. Hamilton, and H.W. Hulan. 1995. The effect of dietary herring meal on the omega-3 fatty acid content of plasma and egg yolk lipids of laying hens. Canadian Journal of Animal Science, 75:247-253.
* Neely, E. 1999. Dietary modification of egg yolk lipids. Thesis. School of Agriculture and Food Science, The Queeńs University of Belfast, Northern Ireland, UK.
* Novak, C. and S. Scheideler. 1998. The effect of calcium and/or vitamin D, supplementation of flax based diets on production parameters and egg composition. University of Nebraska Cooperative Extension MP 70, Lincoln, USA..
* Oomah, B.D. and E.O. Kenaschuk. 1995. Cultivars and agronomic aspects. Pages 43-45 in Flaxseed in Human Nutrition, edited by S.C. Cunnane and L.U. Thompson. American Oil Chemists’ Society Press, Champaign, USA.
* Porsgaard, T., and C.E. Høy. 2000. Lymphatic transport in rats of several dietary fats differing in fatty acid profile and triacyglycerol structure. Journal of Nutrition, 130:1619-1624.
* Sebedio, J.L. 1995. Marine oils. Pages 266-299 in Oils & Fats Manual, edited by A. Karleskind Lavoisier Publishing, Paris, France.
* Scheideler, S.E., G. Froning, and S. Cuppett. 1997. Studies of consumer acceptance of high omega-3 fatty acid-enriched eggs. Journal of Applied Poultry Research, 6:137-146.
* Shukla, V.K.S. and E.G. Perkins. 1998. Rancidity in encapsulated health-food oils. INFORM, 9(10):955-961.
* Shukla, V.K.S., P.K.J.P.D. Wanasundra, and F. Shahidi. 1996. Natural antioxidants from oilseeds. Pages 97-132 in Natural Antioxidants, edited by F. Shahidi. American Oil Chemistś Press, Champaign, USA.
* Simopoulos, A.P. 1999. Essential fatty acids in health and chronic disease. American Journal of Clinical Nutrition, 70(3):560S-569S.
* Simopoulos, A.P. and N. Salem Jr. 1992. Egg yolk as a source of long-chain polyunsaturated fatty acids in infant feeding. American Journal of Clinical Nutrition, 55:411-414.
* Straarup, E.M., and C.E. Høy. 2000. Structured lipids improve fat absorption in normal and malabsorbing rats. Journal of Nutrition, 130:2802-2808.
* Taga, M.S., E.E. Miller, and D.E. Pratt, 1984. Chia seeds as a source of natural lipid antioxidants. Journal of American Oil Chemists’ Society, 61:928-931.
* Tengerdy, R.P., and J.C. Brown. 1977. Effect of vitamin E and A on humoral inmunity and phagocytosis in E. coli infected chicken. Poultry Science, 56:957-963.
* Ting, I.P., J.H. Brown, H.H. Naqvi, J. Kumamoto, and M. Matsumura. 1990. Chia: a potential oil crop for arid zones. Pages 197-202 in H.H. Naqvi, A. Estilai, and I.P. Ting eds. New Industrial Crops and Products. Proceedings of The First International Conference on New Industrial Crops and Products, Riverside, California, USA, October 8-12, 1990.
* Treviño, J., M.L. Rodriguez, L.T. Ortiz, A. Rebole, and C. Alzueta. 2000. Protein quality of linseed for growing broiler chicks. Animal Food Science and Technology, 84:155-166.
* United States Department of Agriculture. 1999. USDA Nutrient database for standard reference, release 13. Agricultural Research Service, Nutrient Data Laboratory Home Page, Download 26/3/01, https://www.nal.usda.gov/fnic/foodcomp
* Valenzuela, A. and R. Uauy. 1999. Consumption pattern of dietary fats in Chile: n-6 and n-3 fatty acids. International Journal of Food Sciences and Nutrition, 50:127-133.
* Van Elswyk, M.E., P.L. Dawson, and A.R. Sams. 1995. Dietary menhaden oil influences sensory characteristics and headspace volatiles of shell eggs. Journal of Food Science, 60:85-89.
* Van Elswyk, M.E., B.M. Hargis, J.D. Williams, and P.S. Hargis. 1994. Dietary menhaden oil contributes to hepatic lipidosis in laying hens. Poultry Science, 73:653-662.
* Van Elswyk, M.E., A.R. Sams, and P.S. Hargis. 1992. Composition, functionality, and sensory evaluation of
eggs from hens fed dietary menhaden oil. Journal of Food Science, 57:342-349.
* Wander, R.C., J.A. Hall, J.L. Gradin, S.H. Du, and D.E. Jewell. 1997. The ratio of dietary (n-6) to (n-3) fatty acids influences immune system function, eicosanoid metabolism, lipid peroxidation and vitamin E status in aged dogs. Journal of Nutrition, 127:1198–1205.
* Weber, C.W., H.S. Gentry, E.A. Kohlhepp, and P.R. McCrohan. 1991. The nutritional and chemical evaluation of chia seeds. Ecology of Food and Nutrition, 26:119-125.