Effects of dietary fish oil and flax seed on cholesterol and fatty acid composition of egg yolk and blood parameters of laying hens

 

 

H. Basmacıoğlu^{I, #}; M. Çabuk^II; K. Ünal^III; K. Özkan^I; S. Akkan^I; H. Yalçın^III

^IEge University, Faculty of Agriculture, Department of Animal Science, Bornova-İzmir, Turkey
^IICelal Bayar University, Vocational School, Department of Poultry Science, Akhisar, Manisa-Turkey
^IIIEge University, Faculty of Engineering, Department of Food Engineering, Bornova-İzmir, Turkey

 

 

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ABSTRACT

This study was conducted to determine the effects of the supplementation of different levels of fish oil (FO) and flax seed (FS) in the diets of layers on the content of egg yolk fatty acid, cholesterol, blood parameters, egg production and egg quality criteria. In the experiment, a total of 120 Isa-White laying hens of 34 weeks of age were used. Hens were divided randomly into five groups and fed different diets containing no FO and FS; 1.5% FO; 4.32% FS; 1.5% FO+4.32% FS and 8.64% FS for eight weeks. A significant decrease in yolk cholesterol content (mg/g yolk) was found in the eggs from hens fed the diets containing 1.5 % FO and 8.64% FS as compared with the control. Adding FO and FS to diets significantly increased the total omega-3 fatty acids in eggs at 28 (phase 1) and 56 (phase 2) days of the trial. By contrast, the addition of both FO and FS to diets had no effect on total omega-6 fatty acids in eggs in phase 1. But dietary 1.5% FO, 4.32% FS and 1.5% FO+4.32% FS supplementation decreased significantly the total omega-6 fatty acids compared to the controls in phase 2. The linolenic acid content of eggs was the highest in eggs from hens fed the diet with added FS, while docosahexaenoic acid content was the highest in eggs from hens fed diets with added FO. Dietary supplementation of FO and FS did not significantly affect the concentrations of serum trigliceride and high density lipoprotein. The serum cholesterol level of hens fed diets containing 1.5% FO+4.32% FS and 8.64% FS was lower than the control group. The addition of FO and FS to diets did not cause any negative effect on some egg quality criteria such as egg weight, yolk weight, yolk ratio, albumen weight, albumen ratio, shell weight, shell ratio, shell strength and shell thickness. The egg production of hens fed a diet containing 4.32% FS was significantly higher than the controls. Feed intake and feed conversion were not affected by all treatments.

Keywords: Omega-3 fatty acids, cholesterol, eggs, flax seed, fish oil

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Introduction

The egg is one of the most complete foods from a nutritional point of view. However, consumers refrain from egg consumption due to the relatively high cholesterol content of eggs and the perception that cholesterol rich foods lead to coronary heart disease (CHD) and atheriosclerosis (Zeidler, 1998). Risk factors for CHD include hypertension, obesity and elevated blood cholesterol concentrations. The occurrence of CHD was higher in humans who have high blood cholesterol levels. Nutrition, genetics, age and sex affect blood cholesterol levels in humans. During the past 20 years public concern has focused on the relationship between dietary cholesterol and the development of CHD. However, dietary fat type and fatty acid composition of fats consumed, are more important than the amount of dietary cholesterol consumed (Leskanich & Noble, 1997; Simopoulos, 2000b). According to the results of many studies, it was confirmed that saturated fatty acids and trans fatty acids cause negative effects on human health, but polyunsaturated fatty acids (PUFA) have a positive effect on human health as regards CHD (Blanch & Grashorn, 1995; Bhatnagar & Durrington, 2003; Erkkila et al., 2003; Meyer et al., 2003). In recent years, consumer demands for more healthy foods stimulated the interest in modifying the fatty acid profile of eggs. Over the past 20 years many studies and clinical investigations revealed that omega-3 PUFA, particularly eicosapentaenoic (EPA) and docosahexaenoic (DHA) exert beneficial effects on human health. Omega-3 PUFA are essential for normal growth and development and many play an important role in the prevention and treatment of CHD, hypertension, inflammatory, autoimmune disorders and cancer (Meluzzi et al., 1997a; Lewis et al., 2000; Simopoulos, 2000a). Eggs and poultry meat rich in omega-3 fatty acids can be produced by using feed ingredients rich in omega-3 fatty acids. In general, studies have been conducted to determine the effects of different omega-3 fatty acids sources in diets on the cholesterol and fatty acid composition of egg yolk and meat (Caston & Leeson, 1990; Cherian & Sim, 1991; Hammershøj, 1997; Coetzee & Hoffman, 2002; Komprda et al., 2003). However, studies with regard to the effects of omega-3 fatty acids on blood cholesterol are lacking. In addition, in many studies the most important criteria such as egg yolk cholesterol and fatty acid content of eggs, blood cholesterol, the performance of layers and egg quality criteria were not fully determined (Caston & Leeson, 1990; Cherian & Sim, 1991; Jiang et al., 1991; Herber & Van Elswyk, 1996; Hammershąj, 1997; Niemiec et al, 1997).

In this study, the effects were studied of adding fish oil and flax seed to layers diets on the cholesterol and fatty acid content of egg yolk, blood parameters, the performance of layers and egg quality criteria.

 

Materials and Methods

One hundred and twenty 34-week old Isa-White laying hens were randomly allocated to five experimental treatments. Each treatment consisted of six replications, with a replication consisting of four hens in a cage. The cages were kept in an open-sided layer house and the experiment lasted for eight weeks. The experimental diets were: A control diet (C) containing no fish oil (FO) or flax seed (FS); treatment FO containing 1.5% fish oil; treatment FS1 containing 4.32% flax seed; treatment FO+FS with 1.5% fish oil +4.32% flax seed and treatment FS2 containing 8.64% flax seed. The 4.32 and 8.64% FS were added to provide 1.5 and 3.0% flax seed oil to the respective diets. The experimental diets were formulated to be iso-energetic (11.5 MJ ME /kg DM) and isonitrogenous (16.5% crude protein). The ingredient and chemical composition of the experiment diets are presented in Table 1 and their fatty acid composition in Table 2.

To determine cholesterol and fatty acid content of egg yolk, six eggs were collected after 28 days (phase 1) and after 56 days (phase 2) from each treatment. In order to determine serum cholesterol, triacylglycerol and high density lipoprotein (HDL) concentrations, a total of 30 blood samples (six samples per group) were taken from the wing vein, after feed withdrawal for 12 h. After coagulation, the blood was centrifuged at 2000 rpm to obtain the serum. The serum parameters were analysed by auto analyzer (Opera technicon®), using commercial kits (Sigma Diagnostic® Kits). A direct saponification procedure was applied for the analysis of cholesterol in egg samples (Poyraz, 1987). Lipids were extracted from eggs using the method of the AOAC (1990). The fatty acid methyl esters were prepared from lipid samples according to Joseph & Ackman (1992) and from subsequent fatty acid profiles obtained by gas liquid chromatography (GLC). The fatty acid methyl esters were analysed using a 50 x 0.25 mm inside diameter WCOT fused silica CP-Sil 88 capillary column installed in a Hewlett Packard 5890 GLC with flame ionization detector. Egg production was recorded daily and calculated as hen-day (%). Feed consumption (g/hen/day) and feed conversion as kg feed consumed/kg eggs were recorded at 28 and 56 days of the trial. Egg quality criteria (egg weight, yolk weight, yolk ratio, albumen weight, albumen ratio, shell weight, shell ratio, shell strength and shell thickness) were measured at 28 days and 56 days of the trial, using 18 eggs from each experimental unit. Mortality was recorded daily. The standard techniques for the Proximate analysis were used to determine the nutrient concentrations in the diets (Naumann & Bassler, 1993). The experimental diets were analysed also for starch, sugar, total calcium and phosphorus, according to VDLUFA method (Naumann & Bassler, 1993). Metabolisable energy content of the diets was calculated based on their chemical composition (Anonymous, 1991). The data were analysed statistically using the General Linear Models procedure of SAS (1985). Significant differences between treatment means were separated using the Duncan's multiple range test with a 5% probability.

 

Results and Discussion

The cholesterol contents in both the egg yolk and eggs of layers decreased significantly (P < 0.05) with increasing age (Table 3). The finding that cholesterol content of egg yolk in layers decreased with increasing age agrees with the findings of previous research (Oltjen & Dinius, 1975; Gissel et al., 1976; Brendl et al., 1979; Basmacıoğlu & Ergül, 2000). It was previously reported that the cholesterol content in eggs increased with age and this increase resulted from an increase in both egg and yolk weights (Oltjen & Dinius, 1975; Basmacıoğlu & Ergül, 2000).

A significant decrease in yolk cholesterol concentration (mg/g yolk) was found in the eggs from the hens receiving the diets containing 1.5% FO and 8.64% FS as compared with the control. Lin & Pratt (1992) reported that when omega-3 fatty acid rich 3% menhaden oil was added to the diet, yolk cholesterol concentration (mg/g yolk) decreased by 15%. In addition, it was reported that fish oil (Meluzzi et al. 1997b) or flax seed (Caston & Leeson, 1990) did not effect the egg yolk cholesterol concentration (mg/egg). Our results (Table 3) agree with these findings.

Fatty acid composition of eggs obtained at the end of the first phase is given in Table 4, while that obtained at the end of the second phase of the trial is summarized in Table 5. Adding FO and FS to the diets significantly increased the amount of total omega-3 fatty acids in both phases. The total saturated fatty acids decreased in both phases of the experiment, and was significant (P < 0.05) except for layers fed the 1.5% FO in phase 1. Total omega-3 fatty acid concentrations increased more in eggs obtained from layers fed both FO and FS than those fed either FO or FS. A five fold increase (P < 0.05) in the concentration of DHA in eggs was recorded when the hens received the diet containing 1.5% FO, compared to the control diet. These results were similar to those reported by Caston & Leeson (1990), Cherian & Sim (1991), Hargis et al. (1991), Scheideler & Froning (1996), Gonzalez-Esquerra & Leeson (2000) and Meluzzi et al. (2000). The highest levels of linolenic acid, which is also a omega-3 fatty acid, were detected in eggs of layers fed the diets containing FS. Due to the increase in omega-3 fatty acids and decrease in omega-6 fatty acids in eggs, the ratio of omega-6/omega-3 in eggs was reduced from 12.64 to 2.27 at day 28 of the trial and from 14.56 to 2.28 at day 56.

Adding FO and FS to the diets did not affect the total omega-6 fatty acid content of yolk at day 28 of the trial. Dietary supplementation of 1.5% FO, 4.32% FS and 1.5% FO+4.32% FS decreased (P < 0.05) the concentration of total omega-6 fatty acids of yolk compared to controls at day 56 of the trial. Jiang et al. (1991) found that there were no significant changes in the total omega-6 fatty acid content of yolk at a dietary inclusion of 15% FS, compared to their control.

Inclusion of FO and FS in the diet did not affect (P > 0.05) the triacylglycerol and HDL cholesterol concentrations of the serum of the hens. Supplementation with 1.5% FO+4.32 FS and 8.64% FS to diets decreased (P < 0.05) serum cholesterol concentration (Table 6). Our finding was similar to that of Van Elswyk et al. (1994) who demonstrated that dietary FO supplementation at a 3.0% inclusion level resulted in a decreased serum cholesterol concentration in hens.

While adding FO to the diet did not cause a significant difference in egg production, 4.32% FS supplementation increased egg production (P < 0.01) compared to hens receiving 8.64% FS, 4.32% FS+ 1.5% FO and the control (Table 7). This finding is similar to that of Hargis et al. (1991) who determined that FO was not effective in egg production. Jiang et al. (1991), who included FS at a 15% level and Yannokopoulos et al. (1999), who used FS at levels of 5, 10 and 15% reported that FS did not effect egg production. However, Scheideler & Froning (1996) reported that 1.5% FO and 5, 10 and 15% FS increased egg production significantly (P < 0.05). Feed intake and feed conversion were not affected by any of the treatments. From the egg quality criteria determined, only egg and yolk weights increased significantly with the age of the hen (Table 8).

Feeding dietary FO and FS did not affect (P > 0.05) the determined egg quality criteria. This finding is similar to those of other researchers (Voght & Harnisch, 1978; Roland, 1979; Hurtwitz, 1987; Basmacioglu & Ergül, 2000). Yannakopoulos et al. (1999) reported that FS used in laying hen diets did not affect egg quality criteria except for egg and yolk weights. Only one mortality occurred, and that amongst the hens receiving the 1.5 FO+ 4.32 FS diet.

 

Conclusions

The results of the present study show that adding FO and FS to the diets of laying hens resulted in up to a 6 fold increase in total omega-3 fatty acids concentration of yolk and a decrease in omega-6/omega-3 ratio of yolk compared to the control. In addition, these supplements did not affect the performance of hens and egg quality criteria adversely. Therefore, it is possible to obtain yolk containing satisfactory amounts of beneficial fatty acids by supplementing the diets with fish oil and flax seed.

 

Acknowledgements

This project was supported by Scientific Research Foundation of Ege University, Turkey (98ZRF-052).

 

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# Corresponding author. E-mail: basmacioglu@ziraat.ege.edu.tr