In recent years, the ratio of n-6 to n-3 polyunsaturated fatty acids (PUFA) has been taken into account in the assessment of nutritional value of dietary fats as well. This ratio is unfavourably high in the diets of developed western countries. The higher dietary intake of n-3 PUFA, especially the longer chain eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) may play a beneficial role in the prevention and treatment of cardiovascular diseases, cancer and inflammatory disorders. Marine fish is a rich source of longer chain n-3 fatty acids. However, seasonal availability, price and consumers’ preference can limit its consumption.
Therefore, an alternative way to provide sufficient n-3 PUFA to the consumer is to incorporate these fatty acids into more conventional food products by nutritional manipulation. The n-3 PUFA rich eggs have already been marketed in the USA and EU. Although several experiments have been conducted in our country as well, the so-called ’’n-3” or
’’omega-3” egg has not been available in Hungary yet. Thus, the aim of this study was to add new information to the future production of ’’n-3”
eggs in Hungary.
The first experiment was conducted to study the influence of two n-3 PUFA sources available in Hungary, such as linseed and cod liver oil on the performance traits of layers and fatty acid composition of egg yolk.
Furthermore, the n-6 PUFA-rich pumpkin seed oil, which has not been used in nutrition of laying hens, was tested in this experiment.
ISA Brown hens (n=168) at 48 weeks of age were housed in a poultry house with a light regime of 16h light : 8h darkness. Hens were fed a control diet and diets supplemented with 2 and 4% linseed, pumpkin seed or cod liver oil. The experimental diets were fed for three weeks. At the end of this period data of egg and yolk weight, egg production and feed consumption of hens were recorded. Total lipid content and fatty acid composition of egg yolk were measured.
The results of the experiment can be summerised as follows.
Supplementation of diets with 2 or 4% linseed, pumpkin seed or cod liver oil did not influence egg weight and proportion of egg yolk as compared to the control diet. Feeding the diet containing 4% pumpkin seed oil, significantly (P < 0.05) increased yolk weight in comparison with the control. At the supplementation level of 4% the lowest egg and yolk
weight were observed in the linseed oil group. Hens fed diets supplemented with cod liver oil showed lower rate of egg production, than hens fed the other diets. Total fat content of egg yolk was not affected by the type and dietary inclusion level of added oils. Total n-3 PUFA content of egg yolk was approximately four to tenfold higher when hens were fed diets supplemented with linsed or cod liver oil compared to the control group. The supplementation of n-3 PUFA-rich oils resulted in 1.6 to 5.5 ratio of total n-6 to n-3 PUFA in the egg yolk. Higher content of total n-3 PUFA was measured when hens were fed diets containing linseed oil than in the cod liver oil group, comparing at the same level of added oils. DHA was the most important (60-70%) n-3 fatty acid in the
FRGOLYHURLOJURXSZKHUHDV -linolenic acid was about 70% of the total n-3 PUFA content in the linseed oil group. The proportion of arachidonic acid was lower after feeding diets supplemented with n-3 PUFA-rich oils as compared to the control. In comparison with the control diet, the ratio of n-6 to n-3 PUFA was increased when pumpkin seed oil was added to the diet.
In conclusion, cod liver oil at the supplementation level of 2% can be recommended to produce eggs rich in n-3 PUFA. The fatty acid composition of these eggs meet the optimal ratio of n-6 to n-3 fatty acids (4:1-10:1). Furthermore, this product can provide a substantial amount of the most beneficial n-3 fatty acids, EPA and DHA to the consumer.
The highly unsaturated nature of n-3 fatty acids predisposes the egg yolk to lipid peroxidation. The oxidative damages of lipids can be prevented or limited by natural antioxidants added to the feed and deposited in the egg.
Therefore, the objective of the 2nd experiment was to investigate the effect of vitamin E supplementation combined with cod liver oil and pumpkin seed oil on the fatty acid composition, vitamin A and E content and oxidative stability of egg yolk.
A total of 144 ISA Brown hens, 54 week old, were housed in the laying house under similar experimental conditions as it was described in the first experiment. A basal diet containing 4% pumpkin seed oil or 4%
cod liver oil was supplemented with 0, 30 and 60 mg/kg dl- -tocopheryl acetate. In addition to the parameters measured in the first experiment, the content of vitamin A and E and oxidative stability of egg yolk, expressed in thiobarbituric acid reactive substance values (TBARS) were determined.
The supplementation of diets with 30 and 60 IU/kg vitamin E did not affect egg weight significantly. Yolk weight and yolk percentage were increased by dietary treatment with 60 IU/kg vitamin E in the pumpkin seed oil group as compared to the diet without added vitamin E. Vitamin E content of diets did not affect the proportion of n-6 and n-3 fatty acids in egg yolk. The added vitamin E level of 30 IU/kg increased the vitmanin E content of yolk significantly as compared to the control in both oil group. However, the supplementation of diets with 60 IU/kg vitamin E was more effective in the cod liver oil than in the pumpkin seed oil group. The concentration of vitamin A in egg yolk was not influenced by different vitamin A contents of diets without added tocopherol. Higher vitamin A content was measured in the egg yolk of hens fed diets supplemented with 30 IU/kg vitamin E as compared to the level of 60 IU/kg in both oil group. TBARS values of egg yolk were significantly (P
< 0.001) related to the concentration of n-3 fatty acids in yolk lipids, however, no relationship was found between TBARS values and total n-6 or total PUFA content. Oxidative stability of yolk was proportionally enKDQFHG E\ GLHWDU\ -tocopheryl acetate treatments in the cod liver oil group, whereas TBARS values in the pumpkin seed oil group remained
FRQVWDQWDIWHU -tocopheryl acetate supplementation. In contrast to vitamin E concentrations, vitamin A contents of egg yolk were not related to TBARS values in either group.
The results of this experiment show that content of n-3 PUFA and vitamin E of egg yolk can be increased together, and it is recommended to protect egg yolk lipids against lipid peroxidation. If diets are supplemented with 4% cod liver oil, at least 70-80 IU/kg dietary level of vitamin E should be used. The content of vitamin A in diets containing 4% cod liver oil did not affect vitamin A and E content, fatty acid composition and oxidative stability of egg yolk.
Several studies with mammals showed that the ratio of n-6 to n-3 PUFA in feed can modify the glucose uptake and insulin sensitivity of sceletal muscle cells, the lipoprotein secretion of liver. Carbohydrate and lipid metabolism of laying birds are fundamentally different from those in mammals. The aim of the 3rd experiment was to evaluate the effect of exogenous insulin and glucagon in vivo on plasma glucose, triglyceride, low (LDL) and very low density lipoprotein (VLDL) concentrations while feeding diets containing different type of fats.
Laying hens of the Lohmann Brown strain at 37 wk of age were housed in individual laying cages. Birds were fed either a low-fat control diet containing 0.5 % soybean oil or diets supplemented with 4 % pumpkin seed oil or 4 % cod liver oil. Egg weight and feed consumption of hens were recorded daily, whereas body weight was measured weekly during the four weeks period before starting hormone treatments. After 4 wk feeding of the experimental diets five hens from each experimental group were randomly selected and implanted with wing vein catheters. Porcine insulin at a dose of 0.5 IU/kg body weight and porcine glucagon at a dose of 20 µg/kg body weight diluted in 1 ml sterile isotonic saline were administered through the catheter. Sterile isotonic saline (1 ml per animal) was used as sham treatment. Blood samples (0.5 ml) were taken 2 to 5 h after the oviposition with the following intervals: 10 min before injection and at 0, 10, 20, 30 and 60 min post-injection. Plasma glucose, triglyceride and LDL + VLDL concentration were determined.
Glucagon administration increased plasma glucose concentration in all dietary groups. The maximum levels of glucose were found in each group at 20 min post-treatment. In the control and cod liver oil groups these peak levels returned to the pre-injection level within 60 min after treatment. However, plasma glucose concentration of the pumpkin seed oil group was still significantly (P < 0.05) higher at 60 min post-injection than those measured at the same sampling time for the two other groups or the basal value of this dietary group (0 min). Exogenous insulin resulted in a decrease of plasma glucose. The minimum values in the control and cod liver oil group were obtained at 20 min after the insulin administration, and plasma glucose reached the pre-treatment (0 min) levels by the time 60 min post-injection. In the pumpkin seed oil group, however, plasma glucose concentration showed a different response curve from those of the other two dietary groups. The dietary regime did not influence the responses of plasma triglyceride and LDL+VLDL concentration to hormone and saline injections. Although glucose concentrations were significantly altered, plasma triglyceride and LDL+VLDL levels were not significantly affected by glucagon or insulin treatment until the end of the sampling period.
In conclusion, the dietary n-6 to n-3 PUFA ratio can modulate the plasma glucose response to glucagon and insulin in laying hens. Fat supplemented diets rich in n-6 PUFA may lead to higher glucagon sensitivity and can alter responsiveness to insulin. Dietary oils high in
long chain n-3 PUFA do not modify the effect of glucagon and insulin on plasma glucose compared to a low-fat diet.