Cholesterol Levels and Nutritional Composition of Commercial Layers Eggs Fed Diets with Different Vegetable Oils

This experiment aimed at evaluating the effects of the supplementation of different vegetable oils at different levels to the diet of commercial layers on egg cholesterol levels and nutritional composition (proteins, total solids, lipids, and ashes) for 112 days. Birds were distributed according to a completely randomized experimental design with 10 treatments (T1 – control; T2 – inclusion of 2.5% rapeseed oil; T3 – inclusion of 2.5% canola oil;


InTRoduCTIon
The enrichment of eggs with polyunsaturated fatty acids (PUFA), particularly with omega-3 fatty acids has attracted the attention of both researchers and the food industry, because these fatty acids are essential for normal body development and play an important role in the prevention of heart diseases, diabetes, arthritis, inflammatory and auto-immune conditions, and cancer (Simopoulos, 2000).
Most egg lipids are concentrated in the yolk, and consist of lipoproteins, phospholipids, triacylglycerols, and cholesterol.The lipid fraction of the yolk is composed of 8.7g saturated fatty acids, 13.2g monounsaturated fatty acids, 3.4 g polyunsaturated fatty acids and 1.120 mg cholesterol per 100 g of fresh yolk (Holland et al., 1997).
Some researchers (Baucells et al., 2000;Grobas et al., 2001;Gómez, 2003;Mazalli et al., 2004) demonstrated the possibility of changing the fatty acid profile of the lipid fraction of eggs by reducing the dietary concentration of some fatty acids (lauric acid and short-chain saturated fatty acids) in exchange of long-chain fatty acids, such as eicosapentaenoic acid (EPA, C20:5n-3) and docosahexaenoic acid (DHA, C22:6n-3), which present more than 18 carbons in their chemical structure.
Cholesterol deposition in the egg yolk can also be affected by nutrition (Hargis et al., 1991).The inclusion of specific feedstuffs in commercial layer diets, such as vegetable oils rich in unsaturated fatty acids used to change egg lipid profile and to reduce egg cholesterol content.Literature results on the possible effect of the diet on egg and blood cholesterol levels are contractor.According to Holland et al. (1980) and Mori (2001), the addition of PUFA-rich oils in in the diet reduces blood and egg cholesterol concentrations.However, other studies showed that yolk cholesterol content cannot be changed because it seems to be constant, independently of dietary factors (Bertechini, 2003).
This study aimed at evaluating the effects of the supplementation of rapeseed, soybean, and canola oil in commercial layer diets on yolk cholesterol levels and composition in terms of total solids, protein, lipids, and minerals.
Table 1 shows the ingredients and the calculated nutritional composition of the experimental diets.
Birds were housed in a brick house with 84 metal cages specific for egg production.Each cage was divided in two compartments with capacity of housing four birds each, housing a total of eight hens per cage.Independent feeders were placed in front of the cage, as well as nipple drinkers.A 17-h of light lighting program was adopted.
Feed intake and egg weight were weekly measured.Yolk chemical composition (protein, total solids, lipid, and ash contents) and yolk cholesterol levels were determined on days 20, 60, and 112 of the experimental period.
Yolk protein content was determined according to the micro-Kjeldahl method, n. 39.1.19, of the AOAC (2007) for total nitrogen determination.The methodology proposed by Silva & Queiroz (2002) was applied to determine the percentage of total solids.Yolk ether extract content was determined according to the methodology described by the AOAC (2007), item 39.1.05.Ash content was determined according to the method described by Silva & Queiroz (2002).
A completely randomized experimental design, with ten treatments with three replicates of six eggs each was applied.
The analyses to determine egg cholesterol content were carried out according to the methodology proposed by Bragagnolo & Rodriguez-Amaya (2003) adapted as suggested by Mazalli et al. (2003), and cholesterol was determined using a commercial enzyme kit.
The option for using the enzymatic method for cholesterol determination was based on the work of Nogueira & Bragagnolo (2002) and Mazzali et al. (2003), who found that there were no cholesterol quantification differences between the enzymatic method, routinely used to determine serum cholesterol levels, and the chromatographic method, routinely used to determine cholesterol content in foods.
Data were submitted to analysis of variance of SAS statistical package (2000), and means were compared by the test of Tukey at 5% significance level.
Yolk cholesterol was analyzed according to a completely randomized experimental design in a 10 x 3 factorial arrangement (10 treatment and three periods), with four replicates per treatment.

RESulTS And dISCuSSIon
Table 2 shows the fatty acid composition of the vegetable oils used in the experimental diets.

Cholesterol Levels and Nutritional Composition of Commercial Layers Eggs Fed Diets with Different Vegetable Oils
Table 4 shows the yolk nutritional composition of the eggs of commercial layers fed diets containing different vegetable oils.
The analysis of variance indicated significant treatment effects on the lipid and mineral composition of the egg yolk, but there was no influence of treatments on yolk total solids and protein contents.Seibel et al. (2005) did not find any differences in albumen or yolk protein content in the eggs of Japanese quails fed diets containing 2.7% fish oil or 5 and 10% of the solid fraction of fish chemical silage for 30 days.
The results obtained in the present study are consistent with the findings of Naber (1979), who asserted that egg protein characteristics are not influenced by the diet.Cobos et al. (1995), working with lipid supplementation of layer diets also did not find any differences in egg protein content.
According to Naber (1979), the main egg component (lipids) may be easily changed by dietary manipulation.Hall & Mckay (1993) found that egg lipid content is influenced by age in domestic fowl.According to Chwalibog (1992), as birds age, egg lipid content increases while protein content decreases.
The results obtained in the present study relative to yolk lipid percentage are consistent with those reported by Fennema (1993), who argues that variations in total yolk lipid content is more influenced by bird genetic strain than diet.Sotelo & Gonzáles (2000), analyzing the percentage composition of egg with low cholesterol levels, found that yolk lipid percentage varied between 29.37 and 30%, which is consistent with the values obtained in the present study.
Relative to mineral composition, yolks from egg produced by hens fed the control treatment (no oil) were significantly different only from those derived from hens fed the diet supplemented with 2.5% canola oil + 2.5% soybean oil, which present lower mineral content.
Yolk mineral content in the present study ranged between 1.76 and 2.05%, which is consistent with the 1.92% determined by Sotelo & Gonzáles (2000) when evaluating the composition of low-cholesterol eggs.
The obtained differences in yolk lipid and mineral contents may be attributed to individual differences inherent to each bird and tis metabolism than to the diet fed, as the yolk composition of eggs produced by layers supplemented or not with vegetable oils were similar.Therefore, it is unlikely that vegetable oil type may have influenced yolk mineral or lipid deposition.

Cholesterol Levels and Nutritional Composition of Commercial Layers Eggs Fed Diets with Different Vegetable Oils
There was a significant interaction between treatments and periods relative to yolk cholesterol content, as shown in Tables 5 and 6.There was a significant interaction between treatment and period for yolk cholesterol content in eggs from layers submitted to all experimental treatments.The highest cholesterol levels in the egg yolk of layers fed the diet with no oil were obtained on days 60 and 112 of the experimental period.
Egg yolks produced by layer fed oils presented lower cholesterol levels after 20 days of inclusion in the experimental diets; however, on day 60, cholesterol levels increased, and were intermediate compared with those recorded on day 112 of the experimental period.It was observed that egg cholesterol content tended to increase as birds aged.These results are consistent with those reported by Beyer & Jensen (1989), who asserted that egg cholesterol level is positively correlated with bird genetics and age, egg weight and yolk weight, and negatively correlated with lay percentage and dietary protein levels.
The high yolk cholesterol content in the eggs of hens fed 5% vegetable oil may be explained by the study of Vargas & Naber (1984), who correlated yolk cholesterol content with dietary energy balance and argued that excessive energy intake, beyond maintenance and production requirements, increases body weight and cholesterol synthesis.Therefore, excessive cholesterol would be transferred to the egg yolk.
Studies on layer dietary manipulation to reduce egg cholesterol content have shown conflicting results.Some report that the polyunsaturated fatty acids that compose the vegetable oils supplemented in the diet reduce both egg and blood cholesterol levels (Harris & Wilcox, 1963;Holland et al., 1980;Mori et al., 1999).On the other hand, these results were not obtained by other authors (Bartov et al., 1971;Wasburn & Nix, 1974), or in the present study.Santos (1998) found that the addition of soybean (2 and 4%), canola (2 and 4%), or polyunsaturated marine (0.1 and 0.2%) to the diet of commercial layers did not affect egg yolk cholesterol levels.

Table 1 -
Ingredients and calculated nutritional composition of the experimental diets.

Table 2 -
Analyzed fatty acid composition of the vegetable oils included in the experimental diets (% of total fatty acids).

Table 3
Means followed by different letters in the same column are statistically different by the test of Tukey (p≤0.05)Faitarone ABG, Garcia EA, Roça R de o, Ricardo H de A, Andrade E n de, Pelícia K, Vercese F

Table 4 -
Percentage composition in the fresh matter of total solids, proteins, lipids, and minerals in the egg yolk of commercial layers fed diets containing different vegetable oils.Means followed by different letters in the same column are statistically different by the test ofTukey (p≤0.05)

Table 5 -
Yolk cholesterol content (mg/100g) of the eggs of commercial layers fed diets containing different vegetable oils.