The Combined Influence of Dietary Flaxseed Variety, Level, Form, and Storage Conditions on Egg ...

METABOLISM AND NUTRITION The Combined Influence of Dietary Flaxseed Variety, Level, Form, and Storage Conditions on Egg Production and Composition Among Vitamin E-Supplemented Hens S. E. SCHEIDELER and G. W. FRONINGi Departments of Animal Science and Food Science and Technology, University of Nebraska, Lincoln, Nebraska 68583-0908 ABSTRACT Trial 1 tested the effects of ground vs whole flaxseed at dietary levels of 5, 10, or 15% compared to a corn-soybean or fish oil control on egg production of Leghorn hens over a period of 8 wk. Dietary flaxseed decreased feed consumption, weight gain, and egg weights compared to the control diets; however, flaxseed and fish oil significantly improved egg production (88.9 and 93.0%, respectively) compared to the control (83.1%). Incorporation of linolenic acid (Ci8:3n-3) m t ° m e e g g increased linearly as the level of dietary flaxseed increased (2.31, 4.18, or 6.83% of the yolk fatty acids for 5, 10, and 15% flaxseed diets, respectively). In Trial 1, flaxseed and fish oil significantly increased percentage white and decreased percentage yolk compared to the control treatment but had no effects on egg cholesterol. Trial 2 was a factorial design

of varieties of flaxseed (brown vs golden), types (ground vs whole), levels of dietary vitamin E (27 vs 50 IU/kg), and feed storage temperatures (4 vs 21 C) fed to hens for 6 wk. Brown flaxseed significantly increased egg weight and egg production compared to the golden variety. There was no difference in whole vs ground flaxseed for measured production variables. Vitamin E (50 IU) significantly improved egg production (96.1 vs 94.3%) compared to 27 IU. Storage temperature of flaxseed did not significantly affect any production variables. In conclusion, dietary flaxseed can be safely added whole to layer diets up to 15% without any detrimental effects on hen-day egg production. Levels of 10 to 15% flaxseed yield eggs with 4 to 7% yolk n-3 fatty acids, respectively, making these eggs rich sources of n-3 fatty acids.

(Key words: flaxseed, layer, egg composition, n-3 fatty acids) 1996 Poultry Science 75:1221-1226

INTRODUCTION Dietary flaxseed is a rich source of linolenic acid that has been shown to dramatically increase the n-3 fatty acid content of eggs (Caston and Leeson; 1990; Jiang et al., 1991, 1992). Flaxseed is one of the most concentrated sources of linolenic acid available in natural plant feedstuffs for poultry. Flaxseed contains as much as 35% ether extract, of which nearly 50% is linolenic acid (Cis : 3n_3). Caston and Leeson (1990) reported a highly significant increase from 0.38 to 8.9% linolenic acid in the egg when diets included 20% flaxseed. Jiang et al. (1992) reported similar increases when feeding 15% flaxseed, but also reported a high incidence (36% of respondents) of fishy flavor in hard-cooked eggs from hens fed flaxseed. The fishy flavor was speculated to have come from oxidation of the flaxseed seed oil prior to consumption by the hens. Altering the fatty acid composition of the egg through dietary ingredients has been well reviewed by Hargis

Received for publication September 8, 1995. Accepted for publication May 30, 1996. Published with the approval of the Director as Paper Number 11256, Journal Series, Nebraska Agricultural Research Division.

and Van Elswyk (1993). The potential health benefit of n-3 fatty acids in the human diet has also drawn attention since the original publication of Dyerberg et al. (1974) reporting a link between dietary n-3 fatty acid consumption and decreased incidence of cardiovascular disease in Eskimos. Linolenic acid has also been reported to be essential for brain development in the young rat (Lamptey and Walker, 1976). A modified n-3 enriched egg could provide a rich alternative source of linolenic acid in the human diet. Variety and physical preparation of the flaxseed seed for poultry diets may affect the palatability, rate of oxidation, and nutrient value of feed and egg products. To date, only the Neche (brown) variety of flaxseed has been tested in poultry diets and it is usually fed in a ground form (Jack Carter, North Dakota Oilseed Council, Fargo, ND 58105-5051; personal communication). The addition of vitamin E and anti-oxidants to rations high in polyunsaturated lipid may prevent oxidation of the feed and potentially of the egg products (Seeman, 1990). The objectives of the trials reported here were to test dietary flaxseed level, ground vs whole flaxseed, variety of flaxseed, and storage temperature of flaxseed, and dietary vitamin E supplementation on egg produc-

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SCHEIDELER AND FRONING TABLE 1. Flaxseed dietary composition, Trial 1

Ingredients and analysis

Control

Fish oil

53.47 5.07

54.16 5.00

20.46 7.00 3.22 0.66 5.00 1.53 2.59 0.35 0.20 0.25 0.10 0.05 0.05

20.36 7.00 1.22 0.64 1.50 4.97 1.53 2.62 0.35 0.20 0.25 0.10 0.05 0.05

18.0 18.5 2,860 1.65 0.09 6.93 2.72 4.00 0.94 0.40 0.51 0.76

18.0 18.2 2,860 1.65 0.12 6.42 2.72 4.00 0.94 0.40 0.51 0.76

5%

10%

15%

(%) Corn Oats Flaxseed Soybean meal Meat bone meal Animal tallow Corn oil Menhaden fish oil1 Oyster shell Dicalcium phosphate Limestone Salt DL-methionine Vitamin E premix2 Vitamin-mineral premix3 Choline chloride Grit Nutrient analysis Protein, calculated Protein, analyzed ME, kcal/kg C18.2 (linoleic acid) C lg:3 (linolenic acid) Ether extract, analyzed Fiber, calculated Calcium, calculated Total phosphorus, calculated Available phosphorus, calculated Methionine, calculated TSAA, calculated

49.73 6.90 5.00 18.10 7.00 3.17

46.30 8.68 10.00 15.70 7.00 2.25

42.87 10.45 15.00 13.30 7.00 1.33

5.00 1.52 2.57 0.35 0.20 0.25 0.10 0.05 0.05

5.00 1.41 2.56 0.35 0.20 0.25 0.10 0.05 0.05

5.00 1.51 2.54 0.35 0.20 0.25 0.10 0.05 0.05

18.0 18.06 2,860 1.96 0.84 7.92 3.06 4.00 0.94 0.40 0.50 0.76

18.0 17.9 2,860 2.63 1.68 8.72 3.39 4.00 0.95 0.40 0.50 0.76

18.0 18.2 2,860 3.32 2.52 9.52 3.73 4.00 0.96 0.40 0.50 0.76

1

Menhaden fish oil was provided by Zapata Protein Inc., Menhaden Oil Refinery, Reedville, VA 22539 and was stabilized with 500 ppm ethoxyquin. Vitamin E premix provided an additional 50 IU/kg vitamin E. 3 Vitamin-mineral premix provided Mn, 88 mg; Cu, 6.6 mg; Fe, 8.5 mg; Zn, 88 mg; Se, 0.30 mg; vitamin A, 6,600 IU; cholecalciferol, 2,805 IU; vitamin E, 10 IU; vitamin K, 2.0 mg; riboflavin, 4.4 mg; pantothenic acid, 6.6 mg; niacin, 24.2 mg; choline, 110 mg; vitamin B12, 8.8 mg; ethoxyquin, 1.1 mg/kg. 2

tion variables, egg composition, and fatty acid profile of the egg yolk.

MATERIALS AND METHODS Trial 1 Eight diets (control, fish oil control, and 5, 10, or 15% whole or ground flaxseed) were fed to four replicate pens with three 43-wk-old DeKalb Delta Single Comb White Leghorn laying hens per pen. Pen density was 688 cm 2 per bird and each pen was equipped with a nipple waterer and a stainless steel feed pan. Diet compositions are given in Table 1. Diets were formulated to meet the daily nutrient requirements of the laying hen at 90% egg production according to NRC (1984) recommendations and to be equal in protein and metabolizable energy content. Nutrient composition of the golden variety of flaxseed used for formulation was 93% dry matter, 6.3% crude fiber, 35.9% ether extract, 5.39% linoleic acid, 16.8% linolenic acid, 3,960 kcal/kg metabolizable energy, 24.0% protein, 0.44% methionine, 0.87% TSAA, 0.89% lysine, 0.55% available phosphorus, and 0.28% calcium (VaiseyGenser, 1994 and Ensminger, 1990). Egg production and feed consumption were measured daily by pen. Hen body

weight was measured weekly and egg weight was measured on 1 d egg production weekly. The birds were fed the experimental diets for 8 wk. At 7 wk, two eggs per pen were collected and saved for determination of percentage yolk, albumen, shell, cholesterol, and yolk fatty acid composition. Eggs were tested individually for a total of eight replicates per diet. Yolk cholesterol and fatty acid composition were determined by gas chromatography methods as reported by Froning et ah (1990).

Trial 2 A 2 x 2 x 2 x 2 factorial arrangement of 16 dietary treatments tested the effects of brown (Neche) vs golden (Omega) varieties of flaxseed, ground vs whole preparation of flaxseed, continuous storage temperature of mixed diets (4 vs 21C), and 27 vs 50 IU/kg supplemental vitamin E. Each diet was fed to four replicate pens of 24-wk-old Babcock B300 laying hens (five hens per pen) for 6 wk. Hens were housed at a cage density of 412 cm 2 per bird with a nipple waterer and stainless steel feed pan for each pen. Nutritive values of the brown and golden varieties of flaxseed were determined by laboratory analysis to be near equal in percentage protein, dry matter, and ether extract. Diet compositions are shown in

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FLAXSEED AND VITAMIN E FOR LAYING HENS TABLE 2. Flaxseed dietary composition, Trial 2 Ingredient Corn Oats Flaxseed Soybean meal Meat bone meal Animal tallow Oyster shell Dicalcium phosphate Limestone Salt DL-methionine Vitamin E premix1 Vitamin-mineral premix3 Choline chloride Grit Nutrient analysis Protein, calculated Protein, analyzed ME, kcal/kg Ci8:2/ 0/° (linoleic acid) C18.3, % (linolenic acid) Ether extract, analyzed Fiber, calculated Calcium, calculated Total phosphorus, calculated Available phosphorus, calculated Methionine, calculated TSAA, calculated Vitamin E, IU/kg

Low Vitamin E

High Vitamin E

46.06 3.75 10.00 20.17 5.17 4.20 2.00 1.77 5.88 0.35 0.19 0.25 0.10 0.05 0.05

45.50 3.75 10.00 20.26 5.18 4.42 2.00 1.77 5.88 0.35 0.19 0.50 0.10 0.05 0.05

18.60 19.0 2,950 2.64 1.68 10.35 2.97 4.00 0.92 0.45 0.50 0.77 27

18.60 19.0 2,950 2.64 1.68 10.55 2.97 4.00 0.92 0.45 0.50 0.77 50

J

Vitamin E premix provided an additional 50 IU/kg Vitamin E. Vitamin-mineral premix provided Mn, 88 mg; Cu, 6.6 mg; Fe, 8.5 mg; Zn, 88 mg; Se, 0.30 mg; vitamin A, 6,600 IU; cholecalciferol, 2,805 IU; vitamin E, 10 IU; vitamin K, 2.0 mg; riboflavin, 4.4 mg; pantothenic acid, 6.6 mg; niacin, 24.2 mg; choline, 110 mg; vitamin B12, 8.8 mg; ethoxyquin, 1.1 mg/kg. 2

Table 2. Flaxseed was included at the 10% level in all 16 diets. Egg production and feed consumption were measured daily by pen. Hen weights were measured biweekly and egg weights on 1 d of production were measured biweekly.

Statistical Analysis Trial 1 was analyzed by the General Linear Models procedure of SAS® (SAS Institute, 1989) and means were separated by Duncan's multiple range test, when the diet effect was significant (P < 0.05) (Snedecor and Cochran, 1980). Contrasts tested were Control vs Flaxseed; Fish Oil vs Flaxseed; and Ground vs Whole Flaxseed for Trial 1. Factorial analysis of the variance of the data for Trial 2 was performed by the General Linear Models procedure of SAS® (SAS Institute, 1989) in which main and interaction effects were tested.

RESULTS Trial 1 dietary effects on egg production variables are given in Table 3. Diet only significantly affected egg weight and egg production. Feed consumption and body weight were significantly affected by the flaxseed dietary treatments relative to the control diets. Birds fed

several of the flax diets (5% whole and ground and 15% ground) exhibited lower feed intakes and reduced body weight. Egg weight responded to dietary treatments with a significant (P < 0.01) decrease in size for the flaxseed (5 and 15% whole and ground flaxseed treatments) vs control and fish oil control diets. Egg production was significantly higher in the fish oil control hens, as well as the overall flaxseed average effect (contrast of control vs flaxseed at P < 0.06). Average egg production for the six flaxseed treatments was 88.9% compared to 83.1% for the control and 93.0% for the fish oil control diets. There was no effect of ground vs whole flaxseed on the production variables measured. Dietary effects on egg components, cholesterol, and fatty acid composition are given in Table 4. Diet significantly affected percentage egg yolk, specifically decreasing egg yolk weight in the fish oil treatment eggs and several of the flaxseed diet eggs. There was a significant decrease in average percentage yolk in eggs produced by hens on the fish oil control or flaxseed diets (contrast P < 0.01) relative to the control treatment. The contrast between ground vs whole flaxseed also was significant (P < 0.01), showing a decreased overall yolk size in eggs fed ground vs whole flaxseed. Percentage eggshell was also significantly affected by dietary treatment with an overall decrease in the flaxseed diets.

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SCHEIDELER AND FRONING

TABLE 3. Trial 1 dietary effect of flaxseed on feed consumption, body weight change, egg weight, and hen-day egg production Dietary treatment

Feed consumption

Control Fish oil control 5% whole flaxseed 5% Ground flaxseed 10% Whole flaxseed 10% Ground flaxseed 15% Whole flaxseed 15% Ground flaxseed SEM

(g/hen/d) 101.4* 103.4" 93.3b 97.1* 101.2* 103.8* 101.3* 97.2* 1.33 d.f. 7

Diet effect Contrasts Control vs flaxseed Fish oil vs flaxseed Ground vs whole

Average body weight a

l,808.1 1,769.5* 1,626.9b 1,687.6* 1,699.6* 1,806.3' 1,683.9* 1,688.0* 51.8

0.05

1 1 1

NS NS NS

Hen day egg production

Egg weight .. .. M \b> 63.5» 63.1* 61.3b 62.3b 62.9* 63.5* 62.3b 61.3b 0.62

(%1 83.1b 93.0a 88.2ab 91.8a 86.3* 91.6a 89.3ab 86.0ab 2.0

0.05

0.01

0.01

0.05

0.01 0.04 NS

0.06 NS NS

NS NS

ab

' Means within a row with no common superscript differ significantly (P < 0.05). Calculated as weight difference between start and end of trial (week 0 and week 8).

This decrease may be due to a laxative effect of flaxseed and increased rate of passage. Diet significantly affected egg fatty acid composition. Only Ci 8 : 2 , Ci 8 : 3 , C22:5, and C22:6 are given in Table 4, and all four were significantly increased with dietary flaxseed or fish oil inclusion. Linoleic acid (Ci8:2) increased when dietary flaxseed was fed at the 15% level. Egg linolenic acid increased linearly (2.31, 4.18, or 6.83% of the yolk) as flaxseed increased from 5 to 10 and 15% of the diet, respectively. The amount of docosapentaenoic acid (DPA) (C22:s) was relatively low compared to the other n-3 fatty acids, but was significantly increased by dietary flaxseed levels' of 10 and 15%. The

presence of docosahexaenoic acid (DHA) (C22:6) in the yolk was highest for the fish oil control treatment (2.87%) but was also significantly increased relative to the control diet for the hens fed flaxseed. The DHA did not respond linearly to level of dietary flaxseed and averaged 1.72% of the yolk fatty acid content. There was no difference between ground vs whole flaxseed on fatty acid incorporation into the egg. Trial 2 dietary effects on production variables are given in Table 5. None of the treatments significantly affected feed consumption or body weight gain. Variety of flaxseed did significantly affect egg weight and rate of egg production. The brown variety produced more egg

TABLE 4. Trial 1 dietary effects of flaxseed on egg components, yolk cholesterol, and yolk fatty acid composition Dietary treatment

Egg white

Egg yolk

Control Fish oil control 5% Whole flaxseed 5% Ground flaxseed 10% Whole flaxseed 10% Ground flaxseed 15% Whole flaxseed 15% Ground flaxseed SEM

57.2 59.5 59 60.3 57.5 58.8 57.9 59.2 0.51

29.2a 27.6* 28.0* 26.1= 29.5a 28.2b 28.6b 28.2* 0.20

(%) -

Diet effect Contrasts Control vs flaxseed Fish oil vs flaxseed Ground vs whole

C18:2 Cholesterol (linoleic)

Eggshell

d.f. 7

NS

0.01

1 1 1

NS NS NS

0.01 NS 0.01

—

( m g/g y° lk )

(linolenic) (%

-22:5

(DPA)1

C22:6 (DHA)2

of total w e i g h t )

12.67bc 13.33b 12.42= 12.51c 12.49= 13.02b= 14.6a 14.813 0.96

0.26d 0.38d 2.01= 2.61= 4.23b 4.13b 7.07a 6.59a 0.81

O.OOd 0.076=d 0.050= d 0.039 b =d 0.088b= 0.109b= 0.154* 0.195a 0.063

0.52Means within a row with no common superscript differ significantly (P < 0.05). 1 Docosapentaenoic acid. 2 Docosahexaenoic acid. Downloaded from https://academic.oup.com/ps/article-abstract/75/10/1221/1515238/The-Combined-Influence-of-Dietary-Flaxseed-Variety by guest on 13 October 2017

FLAXSEED AND VITAMIN E FOR LAYING HENS

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TABLE 5. Trial two dietary effects of flaxseed variety, type, storage, and vitamin E on feed consumption, body weight, egg weight, and hen-day egg production Variety

Type

Storage temperature

Vitamin E

Brown Brown Brown Brown Golden Golden Golden Golden Brown Brown Brown Brown Golden Golden Golden Golden SEM (P value) Variety Golden Brown (P value) Type Whole Ground (P value)

Whole Whole Ground Ground Whole Whole Ground Ground Whole Whole Ground Ground Whole Whole Ground Ground

(C) 40 70 40 70 40 70 40 70 40 70 40 70 40 70 40 70

(IU/kg) 27 27 27 27 27 27 27 27 50 50 50 50 50 50 50 50

Feed consumption

Body weight gain

(g/hen/d) 102.1 92.1 101.7 96.6 96.9 94.5 94.1 95.5 98.2 99.9 98.0 97.9 96.9 100.8 97.0 94.5 2.93 NS 96.3 98.3 NS 97.7 96.9 NS

Storage temperature 40 C 70 C (P value) Vitamin E 27 IU/kg 50 IU/kg (P value)

98.1 96.5 NS 96.7 97.9 NS

mass (56.5 g at 96.5% egg production) than the golden variety (55.8 g at 93.9% egg production). Preparation of flaxseed (ground vs whole) and storage temperature had no significant effect on any of the production variables. Body weight gain was significantly improved in the ground flaxseed group compared to whole flaxseed and in the low vitamin E supplement group (27 IU/kg). Level of dietary vitamin E did affect (P < 0.06) egg production, with the hens fed 50 IU/kg vitamin E producing 96.1% hen-day egg production and the hens fed 27 IU/kg vitamin E producing 94.3% hen-day egg production. Interaction effects (two- and three-way) among treatments were limited. Storage by vitamin E and flaxseed by storage interaction effects on feed consumption were significant (P < 0.05).

DISCUSSION The effect of flaxseed on egg production characteristics in laying hens was discussed briefly by Jiang et al. (1991), in which 16-mo-old laying hens were fed ground flaxseed for only 4 wk. Jiang and coworkers found no

Egg weight

Hen-day egg production

73.4 65.5 83.1 57.1 34.8 33.1 43.9 131.0 61.5 48.5 100.5 85.4 53.4 160.6 117.8 118.4 2.88 NS

55.7 56.3 55.8 56.9 55.6 57.2 54.8 56.3 57.0 56.4 57.2 56.9 55.9 56.5 55.5 55.0 0.20 NS

97.3 95.4 96.8 96.2 92.4 91.4 91.9 93.2 94.1 97.8 98.6 95.9 94.6 94.4 97.8 95.8 2.44 NS

65.2 60.2 NS

55.8 56.5 0.05

93.9 96.5 0.01

56.3 56.0 NS

94.7 95.8 NS

56.0 56.4 NS

95.4 95.0 NS

56.1 56.3 NS

94.3 96.1 0.06

(%)

fM

(hi

53.0 72.5 0.03

61.2 64.2 NS 71.9 53.6 0.03

effect of flaxseed on egg production, egg weight, or specific gravity during that short trial. The results of the studies reported herein demonstrate a positive effect of flaxseed or fish oil on egg production and an effect of variety of flaxseed on egg production, with the brown (Neche) variety having greater effect on egg production than the golden (Omega) variety. These trials were conducted with hens in peak egg production as compared to the older hens utilized by Jiang et al. (1991, 1992). Caston et al. (1994) reported negative effects of dietary flaxseed levels up to 20% on hen weight gain at 51 and 73 wk of age but no significant effects on total egg production. Aymond and Van Elswyk (1995) also reported decreased production in hens fed high levels of flaxseed (15%) over a 5-wk period in y o u n g 22-wk-old hens. Previous studies with flaxseed (Caston and Leeson, 1990; Jiang et al, 1991, 1992) do not state which variety of flaxseed was utilized; most likely it was a brown variety because the golden variety (Omega) tested in Trial 2 is a recent development of North Dakota State University. There was a consistent effect of fish oil and flaxseed on decreasing yolk size and egg weight in these trials.

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This result may have been related to the effect of long chain fatty acids on estrogen activity in the hen, as reported by Whitehead et al, (1993). Whitehead and coworkers found decreased egg weights in eggs from hens fed fish oil compared to those fed corn oil, and a corresponding decrease in plasma estradiol concentration. Whitehead et al. (1993) postulated nutritional regulation of hormonal metabolism by dietary fat in the laying hen. Previous reports of flaxseed use in laying hen diets have all used ground flaxseed (Caston and Leeson, 1990; Jiang et al, 1991; 1992). Considering the laying hen's capacity to grind coarse seed in the gizzard, it is reasonable to postulate that the flaxseed, which has a relative soft seed coat, could be adequately ground for digestion. This effect was proven in Trials 1 and 2 reported here, which showed essentially no significant differences between ground vs whole flaxseed for any of the production or egg variables measured. Differences between whole vs ground flax at any of the various levels of flax treatment (5, 10 or 15%) were significant only for percentage yolk, showing improvement in yolk size with whole flax. This finding does not support the report of Aymond and Van Elswyk (1995), who reported greater deposition of n-3 fatty acids in eggs from hens fed 15% ground vs whole flaxseed. An advantage of feeding whole flaxseed is reduced potential for lipid oxidation during feed storage. Incorporation of fatty acids into yolk from flaxseed was similar to those reported by Caston and Leeson (1990); and Jaing et al. (1991) for linoleic acid (C 18:2 ) and linolenic acid (Ci8:3)- Caston and Leeson (1990) reported 14.6% linoleic acid and 4.6% linolenic acid in eggs from hens fed 10% flaxseed; similar to the values reported in this paper; 12.76% linoleic acid and 4.18% linolenic acid in eggs of hens fed 10% flaxseed. Jiang et al. (1991) reported 6.9% linolenic acid in eggs from hens fed 15% flaxseed, which is comparable to the 6.83% linolenic acid found in eggs produced in this study from hens fed 15% flaxseed. The levels of DPA (C225) were lower and those of DHA (C22:6) were higher in these studies than in the study of Caston and Leeson (1990). The consistency of incorporation of linolenic acid (Ciss) from flaxseed into the egg helps ensure a reliable and consistent egg product for human consumption in the designer food market (Hargis and Van Elswyk, 1993). The independent positive effect of Vitamin E supplementation to 50 I U / k g of diet in Trial 2 was unprecedented. This effect was during peak production of the laying hen and amounted to a 2% increase in henday egg production. Follow-up studies on the role and requirement of vitamin E in laying hens during peak egg production are probably warranted based on the observations of Trial 2 in these studies. In conclusion, up to 15% whole flaxseed can be fed to laying hens during peak egg production with no detrimental effects on egg production. The brown (Neche) variety is the superior variety for egg produc-

tion. Incorporation of linolenic acid (Ci8:3) into the egg yolk is a predictable function based on percentage flaxseed fed in the diet.

ACKNOWLEDGMENTS Authors would like to thank Lyle Robeson and Lynn Niemann for their technical support, Barbara Gnirk and Minnie Stephens for their secretarial assistance. The North Dakota Oilseed Council is sincerely thanked for their financial support of these projects.

REFERENCES Aymond, 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 Sci. 74: 1358-1394. Caston, L., and S. Leeson, 1990. Research note: dietary flaxseed and egg composition. Poultry Sci. 69:1617-1620. Caston, L. J., E. S. Squires, and S. Lessen, 1994. Hen performance, egg quality, and the sensory evaluation of eggs from SCWL hens fed dietary flax. Can. J. Anim. Sci. 74:347-353. Dyerberg, J., H. O. Bang, and N. Hjorne, 1974. Fatty acid composition of the plasma lipids in Greenland Eskimos. Am. J. Clin. Nutr. 28:958-966. Ensminger, M. E., J. E. Oldfield, and W. W. Heinemann, 1990. Feeds and Nutrition Digest. Ensminger Publishing Co., Clovis, CA 93612. Froning, G. W., R. L. Wehling, S. L. Cuppett, M. M. Pierce, L. Niemann, and S. K. Siekman, 1990. Extraction of cholesterol and other lipids from dried yolk using supercritical carbon dioxide. J. Food Sci. 55:95-98. Hargis, P. S., and M. E. Van Elswyk, 1993. Manipulating the fatty acid composition of poultry meat and eggs for the health conscious consumer. World's Poultry Sci. J. 49: 251-264. Jiang, Z., D. U. Ahn, and J. S. Sim, 1991. Effect of feeding flaxseed and two types of sunflower seed on fatty acid compositions of yolk lipid classes. Poultry Sci. 70: 2467-2475. Jiang, A., D. U. Ahn, L. Ladner, and J. S. Sim, 1992. Influence of feeding full-fat flaxseed and sunflower seeds on internal and sensory qualities of eggs. Poultry Sci. 71:378-382. Lamptey, M. S., and B. L. Walker, 1976. A possible role for dietary linolenic acid in the development of the young rat. J. Nutr. 106:86-92. National Research Council, 1984. Nutrient Requirements of Poultry. 8th rev. ed. National Academy Press, Washington, DC. SAS Institute, 1989. SAS/STAT® Users Guide. Version 6, 4th ed., Vol. 2. SAS Institute Inc., Cary, NC. Seeman, M., 1990. The role of vitamin E and antioxidants in feed (II) They maintain food quality. World Poult. (Aug./ Sept.):13. Snedecor, G. W., and W. G. Cochran, 1980. Statistical Methods. 7th ed. Iowa State University Press, Ames, IA. Vaisey-Genser, 1994. Flaxseed Health, Nutrition and Functionality. The Flax Council of Canada, Winnepeg, MB, Canada. Whitehead, C. C, A. S. Bowman, and H. D. Griffin, 1993. Regulation of plasma oestrogens by dietary fats in the laying hen: relationships with egg weight. Br. Poult. Sci. 34:999-010.

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