Chicken meat is considered as an easily available source of high-quality protein and other nutrients that are necessary for proper body functioning. In order to meet the consumers' growing demands for high-quality protein, the poultry industry focused on selection of fast-growing broilers, which reach a body mass of about 2.5 kg within 6-week-intensive fattening. Relatively low sales prices of chicken meat, in comparison to other types of meat, speak in favor of the increased chicken meat consumption. In addition, chicken meat is known by its nutritional quality, as it contains significant amount of high-quality and easily digestible protein and a low portion of saturated fat. Therefore, chicken meat is recommended for consumption by all age groups. The technological parameters of chicken meat quality are related to various factors (keeping conditions, feeding treatment, feed composition, transport, stress before slaughter, etc.). Composition of chicken meat can be influenced through modification of chicken feed composition (addition of different types of oils, vitamins, microelements and amino acids), to produce meat enriched with functional ingredients (n-3 PUFA, carnosine, selenium and vitamin E). By this way, chicken meat becomes a foodstuff with added value, which, in addition to high-quality nutritional composition, also contains ingredients that are beneficial to human health.

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A 4-week experiment was carried out on 360 laying hens of the Hy Line Brown hybrid. Laying hens were divided into three groups (C, E 1 and E 2 ) with 120 hens in each group and kept in 24 cages. Hens were fed layer diets containing 18% of crude protein and 11.60 MJ ME. Hens in the control group C were fed diets that contained 0.2 mg/kg of inorganic selenium (sodium selenite). Experimental groups E 1 and E 2 were given diets with increased concentrations of selenium as follows: E 1 = 0.4 mg/kg of selenium (sodium selenite), E 2 = 0.4 mg/kg of organic selenium (SelPlex). Selenium concentration in diets affected significantly the content of selenium in albumen (P < 0.001) and yolk (P < 0.05). The highest concentration of selenium was determined in albumen and yolk of eggs produced in group E 2 (345 ng/g and 783 ng/g, respectively), then in eggs of group E 1 (230 ng/g and 757 ng/g, respectively), and group C had the lowest concentration of selenium in albumen and yolk (181 ng/g and 573 ng/g, respectively). After 28 days of storage at 4 °C, the eggs containing organic selenium had more freshness (VN: C = 32.9, E 1 = 2.60, E 2 = 2.11). It was concluded that higher concentration of organic selenium in eggs was a limiting factor in metabolic processes, which positively affected the indicators of egg freshness. Organic selenium, inorganic selenium, albumen, yolk, egg freshnessSelenium is found in two forms in nature: inorganic and organic. Inorganic selenium refers to different minerals such as selenite, selenate and selenide, and organic selenium is related to amino acids, methionine and cysteine. Outdoor living animals that eat plants take selenium in the form of selenomethionine (SeMet) in concentrations that depend on selenium concentration in soil, which can vary considerably according to area (Reilly 1996). Klapec et al. (2004) reported low concentrations of selenium in soil on the territory of Croatia because of which the selenium content in plant and animal foodstuffs was relatively low (egg = 52.5 ng/g; chicken meat = 115.3 ng/g; onion = 12.4 ng/g; potato = 7.2 ng/g). As a microelement, selenium has manifold importance in animal feed. Its antioxidant properties help protect animals from free radicals caused by oxygen metabolism. Moreover, selenium strengthens the immune system and boosts growth and feathering. As a dietary supplement, selenium reduces negative effects of stress in chickens kept in intensive production conditions, reduces mortality rate of one-day chickens and enhances quality of poultry products. One of the possibilities of enriching feed with selenium is to supplement it with plants fertilized with selenium (MacLeod et al. 1998). Another possibility is to supplement selenium preparations to commercial mixture fed to animals in order to design animal products that differ in their nutritive values from other conventional products available on the market.The aim of our study was to determine the effects of supplementation of organic and inorganic selenium in increased concentrations to the...

This study aimed to modify the feed mixtures of laying hens to enrich the consumer eggs with n-3 polyunsaturated fatty acids (PUFA): α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). One hundred and twenty Tetra-SL laying hens used in the study were divided into three groups of 40 laying hens arranged in five repetitions: C, control with 5% soybean oil; E1, 0.5% fish oil + 0.5% microalgae Schizochytrium limacinum; and E2, 0.75% fish oil + 0.75% microalgae. The composition of the mixtures was balanced at the level of 17.5% raw protein and 11.81 MJ/kg metabolic energy (ME). Feed and water were provided ad libitum, and the experiment lasted for 21 days. In this study, the different physical and chemical properties of eggs, the fatty acid profile and lipid oxidation of fat in egg yolks were analyzed. The results of the study showed that the weight of the egg yolk and that of the shell depended on the feeding treatments (P = 0.014 and P < 0.001), and the weight of eggs and basic parts, as well as the thickness of the shell depended on the storage duration (P < 0.001). The storage time affected the pH of egg yolks and albumen and the reduction in Haugh units and albumen height (P < 0.001). Significant differences were observed in the content of ALA, DHA, Σn-3 PUFA (mg/100 g) and the n-6/n-3 PUFA ratio between the C and E1/E2 egg groups (P < 0.001). The results of the study indicate that it is sufficient to use a lower level of fish oil and the microalgae Schizochytrium limacinum in hens' feed to achieve a satisfactory increase in n-3 PUFA in eggs, while maintaining optimal values of egg quality and freshness indicators.

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