This study is based on the hypothesis that genotype is one of the most important factors which influence not only egglaying and weight, but also the egg quality characteristics. This is especially true in the difference between highly productive foreign crosses (Lohmann, Haysex, Iza, High Line, etc.), which are widely used for egg production, and aboriginal (local) breeds, which are valued in the sociocultural life of local communities and, although less productive but well adapted to local conditions. Comparative analysis of product quality in poultry of different genetic origin would draw attention to the preservation of the gene pool of local poultry breeds, which are carriers of a set of valuable features such as resistance to several diseases and unfriendly environmental conditions, high-quality eggs, and meat and creation of new selectively significant forms.

The State Poultry Research Station of the National Academy of Agrarian Sciences of Ukraine has been working on the conservation of genetic resources of poultry and its use for many years to create hybrids with high egg production and product quality. Both the autochthonous breeds and populations (Poltava Clay) and the breeds and lines of the Ukrainian selection, (factory line H2) of the Plymouth White breed, Birkivska barvysta) created on their basis, are preserved in the gene pool.

Experimental studies involving poultry were approved and endorsed by the Commission on Bioethics of the State Poultry Research Station NAAS (Ukraine) and conducted following the standards of breeding, keeping, and feeding, as well as the recommendations of the European Convention for the protection of vertebrate animals used for experiments or other scientific purposes.

The aboriginal breed of hens of the egg-meat direction of productivity Poltava clay (line 14) is approved as a new selection achievement by the Order of the Ministry of Agrarian Policy of Ukraine No 781/111 from 6.11.07. The bird is characterized by excellent adaptation to local breeding conditions, increased resistance to neoplastic diseases, high preservation (94.4%) at laying ability 123 – 132 eggs per average laying hen at the age 52 weeks, and egg weight 53.6 – 54.7 g at 30 weeks.

Meat and egg chickens of the factory line H2 of the Plymouth Rock breed approved as a selection achievement by the Order of the Ministry of Agrarian Policy and Food of Ukraine No 146 of April 11, 2016, are better known in Ukraine as Hercules. The bird has a well-defined double type of productivity and high adaptive qualities and are characterized by a high live weight of 3.14 kg (chicks) – 4.1 kg (roosters) and egg weight (65.5 – 68.1 g) at 52 weeks of age at egg-laying per average laying hen 114 – 126 pcs. Birds of egg production Birkivska barvysta (line A) are of synthetic origin, they were bred based on crossing chickens White Leghorn and roosters of the local population of colored leghorn. The breed is in the final stages of creation, autosexual, sorting accuracy at the age of up to 98%. The bird lays 250 – 265 eggs per year with an average weight of 50 – 51 g at 30 weeks age, 58 – 59 g – at 52 weeks.

These genetic resources are lower in productivity to foreign commercial hybrids, which are represented in the Ukrainian market but are characterized by extremely valuable features, such as high adaptation to local climatic conditions, resistance to several diseases, unpretentiousness to feed, high product quality. That is, local breeds remain the carriers of valuable hereditary qualities and gene complexes, without which the further breed-forming process would be one-sided.

Physico-morphological qualities of eggs of hens of Ukrainian selection - three initial parental forms (H2 - Plymouth White, 14 - Poltava Clay, A - Birkivska barvysta) and two hybrids (H2x14, 14xA) in different age periods (26, 34, 44 weeks of life) were studied. Adult chickens of domestic selection were kept in two-tier group cage batteries at a planting density of 9.5 – 9.8 species per m2, feeding and keeping conditions of all groups met the standards. The feeding ratio during the egg-laying phase was isoprotein (17% crude protein) and isoenergetic (2650 kcal/kg) and met the norms for hens in terms of basic nutritional values. Dietary ingredients: corn - 49.4%, wheat - 10.0%, sunflower cake - 12.3%, soybean meal - 14.1%, meat and bone meal - 5.0%, bone meal - 1.15%, lysine - 0.08%, methionine - 0.11%, chalk - 7.5%, salt - 0.16%, vitamin premix - 0.2%. A randomized sample of eggs (60 pieces) was evaluated from each experimental group. A total of 900 Ukrainian poultry eggs were evaluated.

At the same time, a comparative analysis of the studied indexes of local poultry with the indexes of imported commercial crosses used in Ukraine (Tetra SL, Tetra H, Super Harko, Lohmann Brown, Haysex White and Brown, High Line) was made. The physical and morphological qualities of eggs from both poultry and final hybrids were studied. Keeping industrial poultry is the group in multilevel cage batteries. Randomized samples of eggs from hens of foreign crosses (60 pieces from each cross) were obtained directly from producers in the. Kharkiv oblast (Ukraine). A total of 720 eggs of the poultry of foreign selection were evaluated.

Freshly laid eggs were examined in the laboratory following such indexes as egg weight (g), shell weight (g), yolk weight (g), albumen weight (g), yolk content, albumen content (%), yolk- albumen ratio, energy value in terms of per 100 g of egg mass (kJ), the content of total lipids in the yolk (%), the fatty acid composition of the yolks (mg/yolk).

Firstly, the eggs were individually weighed with the help of laboratory quadrant scales VLKT-500 (Gosmetr, Russia), after breaking the egg carefully manually separated the yolk from the albumen. Eggshell, including membranes, and yolk were weighed with laboratory quadrant VLKT- 500 scales (Gosmetr, Russia). The yolk was carefully rolled out on a paper towel to remove the rest of the albumen before weighing, and the chalazes were carefully removed with tweezers. All masses of egg components were determined within accuracy to 0.1 g.

The mass of the albumen was calculated by subtracting the mass of the shell and yolk from the initial mass of the egg. Using these indicators, the proportion of yolk and protein was calculated as a percentage of total egg weight, and the yolk-albumen ratio was calculated as the ratio of yolk mass to albumen mass.

The energy value was calculated according to the formula (1) offered by Ostryakova and others. (Ostryakova, Podstreshnyi and Breslavets, 2003).

(1) E = 100 ⋅ ( 16 ⋅ Myo + 2 ⋅ Malb ) / ( Me - Msh )

Where:

E is the energy value of eggs (per 100 g of egg mass), kJ; Me, Msh, Myo, Malb – a mass of eggs, shells, yolks, albumen, g; 16 and 2 are constants of energy content in 1 g of yolk and albumen.

The total lipid content in the yolk and assessment of their fatty acid composition was carried out on eggs of domestic chickens (H2 - Plymouth White, 14 – Poltava clay, A – Birkivska barvysta) and foreign cross Tetra SL at the age of 44 weeks. Lipid extraction was carried out by the Soxhlet method. Lipids from 4 g of yolk were extracted with 150 mL of petroleum ether using a Soxhlet extraction device. The extraction had being lasted for 2 hours at a temperature of 150 °C. The fat content was determined by the gravimetric (weight) method: the residue after extraction was dried and weighed.

To determine the fatty acid composition of the yolks there were selected 5 eggs from each group. The yolks were isolated, weighed, and stored at minus 12 °C for subsequent chromatographic analysis according to the method described in GOST 30418 (1996) “Vegetable oils. The approach to determining the fatty acid composition”. Chromatographic analysis was performed using laboratory gas chromatograph "Crystallux-4000M" with a flame ionization detector and temperature programming, a thermostat for temperatures not lower than 200 °С, with an evaporator for temperatures not lower than 300 °С. Glass gas chromatographic column 2 m long, 2 - 4 mm inner diameter. The following analysis conditions were set on the chromatography: column thermostat temperature - 180 – 190 °С; evaporator temperature – 250 °С; detector oven temperature – 200 °С; carrier gas flow rate – 30 - 40 cm.min^-1; sample volume – about 1 mm of a solution of methyl esters of acids in hexane.

Calculation of calculated egg quality indexes (albumen weight, albumen. and yolk content, egg-yolk ratio, the energy value of eggs) and statistical processing of the material obtained in the experiment (average values and their standard errors) were carried out with the help of statistical analysis of Microsoft Office spreadsheet Excel. The average values were compared using the Tukey test. The significance level for all tests was p <0.01.

The data of physical and morphological qualities of eggs were analyzed using a two-factor dispersion complex (ANOVA) based on breed and age of chickens, using the general procedure of linear models. The data of egg components were analyzed according to the following model (2):

(2) Yijk = μ + Bi + Aj +  ( BA ) ij + eijk

Where:

μ is the total average value; Bi - the effect of the I - їbreed, cross; Aj - the effect of the j`s- age; (BA) ij - the interaction of the i-ї breed, cross with the j`s- age; eijk - accidental error.

The physical and morphological qualities of eggs (egg weight, protein, yolk, and shell) were studied to give the comparative assessment of hybrids, lines and breeds of Ukrainian selection and parental forms and final hybrids of some imported crosses used in Ukraine (Tetra SL, Tetra H, Super Harko, Lohmann Brown, Highsex White and Brown, High Line W36) at different age periods (26, 34 and 44 weeks of life). Several index indicators, based on the obtained data, were calculated: the proportion of albumen and yolk, energy value indicators, and the yolk-albumen ratio.

Most crosses of foreign selection are characterized by high precocity and rapid increase in egg weight, especially in the first months of egg-laying. The birds of local selection, which are mainly a breed of the egg-meat type of productivity, have a lower precocity and slightly lower egg weight (Rizzi and Chiericato, 2005; Di Rosa et al., 2020; Franco et al., 2020).

In our research, the average egg weight of Ukrainian breeds and hybrids was 51.9 g at 26 weeks age and 61.2 g – at 44 weeks, while in foreign crosses it was significantly higher in the respective age periods – 59 g and 64.5 g, respectively.

Parental forms of crosses in the age aspect have been studied taking into account different paces of weight gain of poultry eggs of foreign and local selection, several indicators characterizing the internal qualities of eggs for different breeds, hybrid.

Already at the age of 26 weeks, significant differences (p <0.01) were found between chickens of different origins in such indicators as yolk weight, albumen, and their ratio and energy value of eggs.

Thus, the weight of the yolk in poultry of local and foreign selection at the age of 26 weeks was almost the same and amounted to 14.2 – 14.4 g, although the weight of eggs differed significantly - more than 7.1 g (13.7%). This difference was reflected in the share of yolk, which in local chickens was higher by 4.3% on average and amounted to 28.5% against 24.2% in foreign crosses. In terms of mass and proportion of albumen, the opposite picture was observed. There was a rapid increase in egg mass from the beginning of egg-laying occurred primarily due to an increase in albumen mass in hens of foreign selection. With the same mass of yolk between groups of birds, the mass of albumen in foreign crosses was much higher - by 8 g, as well as its share in the egg - by 5.7%. At this age, there is a significant difference (p <0.01) in the ratio of yolk-albumen – 0.5 in local breeds and hybrids against 0.38 in foreign crosses. Due to the increased yolk content in the egg, the energy value of eggs of the poultry of local selection exceeded the foreign average by an average of 76 kJ (p <0.01).

Similar results were obtained by Lordelo et al. (2020), which at a higher egg weight in a commercial hybrid compared to chickens of some local breeds by 13% recorded a higher proportion of albumen in it by 7.2% and a lower proportion of yolk – by 7.8%.

According to the results of Danchuk and Trach (2017), in highly productive commercial crosses the yolk mass increases with age more than the albumen mass.

In our studies, with the increasing of birds` age, the yolk mass in foreign chicken selection is increased by 17%, in local breeds and hybrids – by almost 30%. At the same time, albumen mass increased by 6% and 22%, respectively. As for the proportion of yolk, for 18 weeks of productivity (from the 26^th to the 44^th week of the life of the bird) there was a slight increase in this indicator in both local and foreign laying hens - in an average of 1.4-1.6%, but there is a predominance of 4.1% for birds of Ukrainian selection, which eggs are characterized by a large yolk.

At the same time, there is a tendency to a slight decrease in the share of egg albumen with the age of poultry in foreign crosses from 62.8% at 26 weeks to 61 – 61.1% at 34 – 44 weeks. These data are relevant to the results of studies by Rizzi and Chiericato (2005), where it was found a decrease in the proportion of protein from 30 to 42 weeks by 0.9 – 2.7% in chickens cross High Line white and High Line brown.

In chickens of local breeds and hybrids from the 26^th to the 34^th week of life there was a slight increase in the proportion of albumen (by 1.6%), but then there was a decrease in this figure by 0.6%.

This difference in the age dependence of the protein content between poultry of local and foreign selection, in our opinion, is explained by the later start of egg-laying in hens of local breeds.

The age-related change in the components of the egg (albumen and yolk) was reflected in its energy value, which directly depends on its content. There was an increase in the energy value of 100 g of egg mass in poultry of local breeds and populations from 665 kJ at the age of 26 weeks to 676.0 kJ at the age of 44 weeks, in foreign birds from 589.0 kJ to 616 kJ, respectively.

According to the results of the evaluation of the influence of various factors on some studied indicators of chicken egg quality (egg weight, yolk weight, yolk content, yolkalbumen ratio, the energy value of eggs), shown in Table 1, the largest and statistically significant contribution to variability of indicators such as weight eggs and yolk weight, had a factor of “bird`s age” 45.5 – 49.2%. The obtained data are also confirmed by the fact that during the experiment (18 weeks) changes in egg weight ranged from 9.3% in foreign birds to 17.9% in local, and by weight of the yolk from 16.9% to 2.1%, respectively.

At the same time, such a relative indicator as the proportion of yolk is the most (38.7%) influenced by the genetic origin of birds. The same high share influence of genotype on the calculated indicators of the yolk- albumen ratio and energy value is 32.5 and 35.2%, respectively. Also, there was a significant impact of unaccounted random factors on these features, which results in a significant increase in random error (43.8 – 52.6%).

Summing up the results of a comparative study of physical and morphological parameters of eggs of Ukrainian and foreign chickens, we can conclude that the genotype has a significant impact on egg quality.

In all studied periods of the experiment (26, 34, and 44 weeks of the birds` life) there were eggs with higher weight from poultry of foreign selection with an advantage of an average of 5.1 – 12.0% depending on the age of chickens, which significantly affected this indicator. However, even though the eggs of local breeds and hybrids had less weight, they had a higher percentage of yolk – 28.5 – 29.9% against 24.2 – 25.8% in imported crosses. Due to the larger share of yolk in the eggs of hens of Ukrainian selection, their energy value (per 100 g of egg mass) also had an advantage over foreign crosses and amounted to 659.0 – 676.0 kJ against 589.0 – 616.0 kJ. Therefore, eggs from chickens of local breeds, which are valued in the socio-cultural life of local communities, may be more popular among consumers who prefer eggs with large yolks. Besides, the high-quality characteristics of eggs of local breeds and populations are evidence of their value set of genes that require comprehensive study, preservation, and use in the creation of new selectively significant forms.

In the next stage of the study, we studied the total lipid content in the egg yolk of chickens of local selection in comparison with foreign cross Tetra SL (final hybrid (FH)). Higher content of lipids in the egg yolks of domestic chickens was found in comparison with the foreign hybrid Tetra SL (Table 2). Also, the lipid content in eggs of the poultry of egg productivity (line A) is by 0.3 g lower than in eggs of hens of meat-egg productivity (H2).

The study of the fatty acid composition of egg yolks showed that palmitic (C16:0), oleic (C18:1) and linoleic (C18:2) acids have the highest content in yolks: their total amount is more than 80% of the total content (Table 3 and Table 4).

In yolks of eggs of hens of local breeds the general maintenance of saturated and unsaturated fatty acids is higher, than at foreign cross, namely: the maintenance of saturated, monounsaturated, and polyunsaturated fatty acids in eggs of hens of domestic selection was within 1.758 – 1.904, 2.495 – 2.610, 1.126 – 1.278 g/yolk, while in the tested eggs of the final hybrid their content was 1.350, 1.873 and 0.981 g/yolk, respectively. It is necessary to pay attention to the lower content of palmitic acid in eggs of a bird of a foreign cross - 978.0 mg/yolk (Table 3). While in chickens of local breeds this indicator was in the range of 1.288 – 1.443 mg/yolk.

The results of studies by Bunea et al. (2017), Antova et al. (2019) and Mi (2019), Xiao et al. (2020), and Ko et al. (2021) support our findings. They proved that the main fatty acids in the lipids were oleic (39.1 – 47.3%) and palmitic (26.0 – 35.5%) acids.

Palmitic acid is known to be a factor in hypercholesterolemia, a disease in which blood cholesterol levels rise to abnormal levels. Cholesterol ensures the stability of cell membranes, is involved in the synthesis of vitamins, bile acids, hormones. But with hypercholesterolemia, is deposited on the walls of blood vessels, affects metabolic processes, and leads to the development of serious complications, including heart attack, stroke, hypertension, and others.

Analyzing the content of palmitic acid in TSL eggs as a percentage of the total content of fatty acid in the yolk, we can find the difference in 2.3% and 2.7% compared to eggs H2 and Poltava Clay, respectively, which does not seem significant (Table 4). The total content of saturated fatty acids (SFA) in the eggs of domestic chickens was at the level of 1.758 – 1.904 mg/yolk (31.78 – 34.66% of the total fatty acids), in the eggs of the Tetra SL hybrid - 1.350 mg/yolk (32.12%). As for polyunsaturated fatty acids (PUFA), in the eggs of domestic breeds, their content was determined in the range of 1.126 – 1.285 mg/yolk (19.96 – 24.22%), in the eggs of foreign hybrids – 0.981 mg/yolk %), which indicates a lower nutritional value of the latter (Table 3 and Table 4).

The total content of PUFA n-6 in eggs of chickens of domestic selection in comparison with the foreign cross was estimated. The amount of PUFA n-6 in eggs of local breeds was at the level of 1085.0 – 1255.0 mg/yolk, foreign cross – 953.0 mg/yolk. The content of PUFA n-3 was 1.5 times higher in H2 eggs compared to TSL – 41.2 mg/yolk, which is more than 16% of the minimum daily intake (Table 3).

In percentage of the total fatty acid content in the eggs of the studied breeds of chickens, the largest number are monounsaturated fatty acids, due to the high content of oleic acid in the range of 37.27 – 41.96% (Table 4). The percentage of fatty acids in the eggs of both domestic and foreign birds was almost at the same level. In general, the fatty acid composition of eggs reported in our studies differs slightly from those reported in other studies (Lordelo et al., 2020; Danchuk and Trach, 2017; Rakonjac et al., 2017; Cherian and Quezada, 2016).