Introduction

Japanese quail (Coturnix japonica) is a migratory bird that was domesticated by the Japanese in the nineteenth century1. There are about 70 breeds and varieties of Japanese quail around the world, which are kept for breeding purposes for meat and eggs, as well as for laboratory purposes2. Quail farming is a branch of the poultry industry that is developing in African, Asian and Latin American countries because quails have a high reproductive rate as they reach sexual maturity at an early age. They have low nutritional requirements, adapt very easily to various environmental conditions, have high resistance to various poultry diseases, and the meat is of good quality3. Adults reach sexual maturity at the age of 7–8 weeks2,4. Other authors, Hussan and Abd-Alsattar3, showed that the average time to reach sexual maturity in Japanese quails was 40.63 days. One female lays approximately 280 eggs during her reproductive period1. According to Lukanov5, approximately 10% of all table eggs in the world come from quails, while meat constitutes 0.2% of global production. According to Lukanov et al.1, depending on the breed and variety, the body weight of an adult varies from 120–140 to 400–450 g. At the 8th week of life, quail meat is a rich source of protein (23.32–24.55 g/100 g) and polyunsaturated fatty acids, minerals and vitamins6,7. The meat also has a low fat content (1.1 -1.3 g/100 g), which accumulates between the tissues, and cholesterol6,8, which is why it is recommended for people who must follow a low-fat diet. Quail meat has gained great popularity among consumers9. Other authors, however, showed that the protein content in the pectoral muscle (22.23–23.38%) is higher compared to the leg muscles (20.49–20.91%)10. The same authors also showed that the meat of Japanese quails at slaughter age (5 weeks) contains 68% water, 19% protein, 10% fat and 3% minerals, and that the fat content in the leg muscle (3.26–3.39%) is higher than in the pectoral muscle (2.21–2.75%)10. Other researchers found that the protein content, iron (Fe) and zinc (Zn) is higher in the meat of free-living quails compared to the meat of farmed quails11. Other studies have shown that the colour (L⃰, a⃰, b⃰) of meat is influenced by the slaughter age of birds12. The authors showed that with the age at slaughter of Japanese quails, the breast muscle of female quails was characterized by a more red colour, while the brightness (L⃰) decreased, with the breast muscle of males being more yellow (b⃰).The high slaughter efficiency index (65.65–77.00%) of Japanese quail proves its high suitability for meat production13. Genchev et al.10 reported that daily consumption of two quails provides the human body with 27–28 g of protein, which is approximately 40% of the requirement, and 11 g of amino acids. Females are characterized by higher body weight, stomach weight and intestinal length compared to males12. However, the difference in body weight between the sexes did not result in significant differences between the female and the male in wingspan or body length14. Other authors have shown that the production results, carcass composition and meat quality (water retention capacity, pH, tenderness) were influenced by bird plumage15. In our previous studies16,17,18, it is showed that the meat quality and the texture and structure of breast muscles in other poultry species were influenced by the genotype and sex of the birds, which prompted us to perform the following research.

The aim of the study was to analyse the influence of the genotype and sex of Japanese and Pharaoh quails on the composition of the carcass, meat quality (chemical composition, physicochemical properties, texture and microstructure), as well as the morphometry of the digestive system and the dimensions of leg bones. The above results are intended to provide consumers with information about which of the above genotypes is characterized by better muscle and meat quality.

A research hypothesis was put forward, which assumed that the genotype and sex of quails influence the quality of meat, the morphometry of the digestive system and the dimensions of leg bones.

Material and methods

The experiment followed the applicable regulations on protecting animals used for scientific or educational purposes. The study and methods were carried out after obtaining the opinion of the Departmental Animal Welfare Team and the permission of the Experimental Unit of the Bydgoszcz University of Science and Technology (No. 17/2010). The ethics committee of Bydgoszcz University of Science and Technology approved the experimental protocols presented in this study. The birds were purchased at the Experimental Farm in Felin of the University of Life Sciences in Lublin.

Experimental design

The research material consisted of Japanese quails (Coturnix japonica) and Pharaoh breed quails. The birds were kept in a windowless building in a cage system. During rearing, the birds were kept in a 4-level battery in cages with dimensions of 100 × 300 cm, maintaining a stocking density of 70 birds per m2 (until the 35th day of the birds’ life). 20 Japanese quails (laying type) and 20 Pharaoh breed quails (meat type) were purchased. The birds were kept in 10 cages, 5 cages each for the genotype. A total of 200 birds were maintained in 10 cages, 100 Japanese quails and 100 Pharaoh breed quails. Twenty birds were kept in each cage. Two males and two females from each cage were randomly selected for the study. At the beginning of rearing, the temperature was 34 °C, which was systematically lowered until the third week of the birds' life, so as to finally obtain an ambient temperature of 21 °C. During rearing, the relative humidity was maintained at 65%. From the 1st to the 14th day of the birds' life, a 24-h light program was used, which was shortened by 2 h every 7 days to ultimately obtain 17 h of light and 7 h of darkness. Cold colour LED lighting (6000 K) with an intensity of 20 lx was used.

Feeding

The birds were fed with a balanced, complete mixture adapted to the age and needs of the birds. From day 1 to 7, the birds received a mixture containing 3,000 kcal/kg, 28% total protein and up to 3% crude fiber, from day 8 to 28, 2,900 kcal/kg, 24% total protein and up to 3.5% crude fiber, and from day 29 to 42 days 2800 kcal/kg, 20% total protein and up to 4% crude fiber.

Carcass analysis

A total of 20 Japanese quails (10 females and 10 males each) and 20 Pharaoh quails (10 females and 10 males each) at the age of 6 weeks were slaughtered (by interrupting the continuity of the spinal cord, cutting blood vessels, bleeding out in accordance with the application submitted to the Ethics Committee and Polish law, Journal of Laws, 2004, No. 70, item 643, §14,6) no measures were used before euthanasia. Then the eviscerated carcasses and viscera were transported to the University Laboratory, where they were chilled for 18 h in cooling cabinet (Hendi, Gądki, Poland) at a temperature of 2 ℃. After cooling, the carcass was weighed and dissected using the simplified method described by Ziołecki and Doruchowski19, during which the skin with subcutaneous fat, the neck without skin, the wings with skin, the leg muscles, the pectoral muscles, the abdominal fat and the remains of the carcass were isolated. The isolated carcass elements were weighed on a PS 1000.R2 scale (Radwag, Radom, Poland). Then, their percentage share in the carcass was calculated based on the formula: ratio of the mass of the element to the mass of the cold gutted carcass × 100%. Slaughter yield was also calculated based on the formula: ratio of the weight of the eviscerated carcass to the body weight before slaughter × 100%.

Physicochemical properties

Instrumental colour measurements

The pectoral and leg muscles were assessed for colour. The test was performed using a MINOLTA CR 400 colorimeter (Konica Minolta, Chiyoda-ku, Japan). The pectoral and leg muscles were assessed in the colour system L*—brightness variable, a*—red variable, b*—yellow variable.

Chemical composition

The basic chemical composition (water, protein and fat content) was determined by near-infrared transmission spectroscopy (NIT), using the FOSS FoodScan™ Lab (FoodScan, Hilleroed, Denmark), using the method described by Wegner et al.17.

The analysis were performed on breast muscles (m. Pectoralis superficialis and m. Pectoralis profundus) and leg muscles (m. Sartorius and m. Femorotibialis).

Texture analysis

Texture (springiness, chewiness, gumminess, hardness, cohesiveness, WB shear force, cutting work—work required to cut the sample) 40 samples of pectoralis major muscle, 20 samples each of Pharaoh quails (10 females and 10 males) and 20 Japanese quails (10 females and 10 males) were heat treated. Texture was assessed according to the muscle profile analysis procedures described by Wegner et al.18.

Microstructure analysis

Samples of the middle part of the pectoralis major muscle were collected for histological analysis from 40 quails. The prepared meat samples were fixed using Sannomiya solution and then dehydrated in alcohol and benzene. The prepared samples were embedded in paraffin blocks. Using a microtome, the blocks were cut into 10 μm sections and then placed on glass slides. The slides were counterstained with hematoxylin and eosin20 and then embedded in Canada balsam. Using the MultiScanBase v. 13 image analysis system (Computer Scanning System Ltd.), the cross-sectional area of the fibers, the perimeter of the fibers, the horizontal diameter of the fibers (H), the vertical diameter of the fibers (V), and the thickness of the perimysium and endomysium were determined.

Anatomical analysis

The weight of: proventriculus, gizzard, liver, heart and spleen was determined using an electronic scale WPS 210/C (Radwag, Radom, Poland) with an accuracy of 0.01 g. The percentage of offal was calculated based on the formula: organ weight/body weight*100%. A measuring tape was then used to measure the length of individual sections of the small intestine (duodenum, jejunum, and ileum), as well as the caeca length and colon length with an accuracy of 1 mm. Using an electronic caliper, measurements of the diameter of individual intestinal segments were made with an accuracy of 0.01 mm. Measurements were made in three places: at the beginning, in the middle and at the end of each intestinal segment. Measurements were made on the leg bones obtained after dissection using an electronic caliper with an accuracy of 0.01 mm. The following lengths were determined on the femur: GL, greatest length; ML, medial length; GB, greatest breadth of proximal end; GD, greatest depth of proximal end; SM, smallest breadth of the corpus; GC, greatest breadth of the distal end; GE, greatest depth of distal end. Then, measurements of the tibia were taken: GL, greatest length; AL, axial length; GD, greatest diagonal of the proximal end; SB, smallest breadth of the corpus; SD, greatest breadth of the distal end; DD, greatest depth of the distal end. The dimensions of the femur and tibia were determined according to the method developed and presented by den Driesch.21.

Statistical analysis

The collected numerical data in this study were characterized by generally accepted methods of statistical analysis. For each tested trait, arithmetic means were calculated for both factors (genotype and sex) and the standard error of the mean (SEM) for both genotypes combined. The Shapiro–Wilk test was used to assess the empirical compliance of the feature distributions with the normal distribution. A parametric test in the form of a two-factor analysis of variance was used for statistical assessment of the influence of genotype and sex on the tested trait. The following linear model was used: Yijk = µ + ai + bj + (a × b)ij + eijk.

where Yijk to is the value of the trait, µ is the overall mean of the trait, ai is the effect of the i-genotype, bj is the effect of j-sex, (a × b)ij is the genotype of birds by sex interaction, eijk is the error, and k is the kth observation for the target trait in the group.

SAS software (SAS Institute, Cary, NC, USA) version 9.4.22 was used to perform statistical calculations. The significance of differences at P < 0.05 was verified between genotypes and between males and females using Tukey's post hoc test.

Ethical approval

The experiment was carried out following the applicable regulations on the use of animals in science (directive no. 2010/63/EU, ARRIVE guidelines). Animal experiments were carried out in accordance with the Polish Animal Welfare Act, and approved by the Local Ethics Committee for Animal Experiments in Bydgoszcz of June 23, 2010 (RESOLUTION No. 17/2010).

Results

Carcass analysis

In this study, there were significant (P < 0.05) differences between genotype and sex in body weight and carcass weight, and in the percentage of most carcass components at 6 weeks of age between Pharaoh quail and Japanese quail (Table 1). Pharaoh quails had significantly higher body weight and carcass weight (P < 0.001), while female quails were significantly heavier by 15.70 g compared to male Japanese quails. Also, the carcass weight of female Japanese quails was significantly (P = 0.038) higher by 12.34 g compared to the carcass weight of males. The percentage of breast and leg muscles was significantly higher in Japanese quail compared to Pharaoh quail regardless of sex (P < 0.001; 0.001, respectively). In turn, the percentage of residues was significantly higher in Pharaoh quail compared to Japanese quail (P < 0.001). Pharaoh quails had a significantly higher share of necks without skin and skin with subcutaneous fat than Japanese quails (P = 0.020; 0.006, respectively). Such a relationship between females in the analysed traits was not demonstrated in this study. However, female Pharaoh quails had a significantly lower percentage of skin with subcutaneous fat compared to males (P = 0.017). Japanese quails also had a significantly lower percentage of wings compared to Pharaoh quails (P = 0.005). In this study, however, a significantly higher percentage of abdominal fat was found in Japanese quails compared to Pharaoh quails (P < 0.001). Additionally, interactions between genotype and sex were noted in the analysed characteristics of carcass weight, slaughter efficiency and the percentage of wings with skin (P < 0.05).

Table 1 Body weight, carcass weight and proportion of carcass elements of Pharaoh and Japanese quails slaughtered at 6 weeks of age.
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Physicochemical properties

Chemical composition

Table 2 shows the results of the determination of the basic chemical composition of the breast and leg muscles. Significant (P < 0.05) differences were found between the content of water and intramuscular fat in the pectoral muscle and leg muscle between the genotypes. The breast and leg muscles of Pharaoh quails, regardless of sex, were characterized by lower fat and higher water content compared to the analysed features in Japanese quails (P < 0.001). Female Pharaoh quails were characterized by higher water content in the breast muscle and leg muscle and lower protein content in the leg muscle and fat content in the breast muscle compared to males. However, the pectoral muscles of male Japanese quails contained less fat compared to the analysed feature in females (P = 0.033). Moreover, a significant interactions between genotype and sex were demonstrated in the content of fat and water in the breast muscles and water in the leg muscles (P < 0.001).

Table 2 Chemical composition of pectoral and leg muscles of Pharaoh and Japanese quails slaughtered at 6 weeks of age.
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Instrumental colour measurements

Analysing the pectoral and leg muscles in terms of colour parameter values (Table 3), significant (P < 0.05) differences were found between genotype and sex in the lightness (L⃰) of the pectoral muscles and the yellowness (b⃰) of the pectoral and leg muscles. The pectoral muscles of Japanese quails were characterized by higher brightness (L⃰) compared to the pectoral muscles of Pharaoh quails, regardless of gender (P < 0.001). A significantly lower L⃰ value was determined in the pectoral muscle of males compared to females, regardless of the genotype (P < 0.001). There was also an interaction between genotype and sex in L⃰ of leg muscles (P = 0.030). The pectoral muscles of Japanese quails were also characterized by significantly higher yellowness (b* = 5.49) compared to the yellowness (b⃰ = 3.48) of the pectoral muscles of Pharaoh quails (P = 0.001). Also, significantly higher yellowness values (b⃰) were found in the leg muscles of males compared to the leg muscles of females, regardless of the genotype (P = 0.049). The redness (a*) was not affected by genotype and sex (P > 0.05). There was also no interaction between genotype and sex in the analyzed color traits, except for the lightness of leg muscles with L⃰ (P = 0.030).

Table 3 Color parameters of pectoral and leg muscles of Pharaoh and Japanese quails slaughtered at 6 weeks of age.
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Texture analysis

Table 4 presents the results of selected textural features of the pectoralis major muscle of Pharaoh and Japanese quails at the age of 6 weeks. Significant (P < 0.05) differences were found in cutting work, hardness, chewiness and gumminess between genotypes and springiness between genotypes and sexes. The pectoral muscles of the Japanese quail had higher values of cutting work and springiness compared to the pectoral muscles of the Pharaoh quail (P = 0.001). However, higher (P < 0.05) hardness, chewiness, and gumminess were determined in the breast muscle of Pharaoh quails compared to the analysed trait of Japanese quails, regardless of sex (P = 0.002–0.037). In turn, greater elasticity of the pectoral muscle was demonstrated in Japanese quails and females compared to the analyzed feature in Pharaoh quails and males (P = 0.001; 0.026, respectively). There were no significant interactions between genotype and sex in the analyzed texture features (P = 0.066–0.799).

Table 4 Texture characteristics of pectoral muscle of Pharaoh and Japanese quails slaughtered at 6 weeks of age.
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Structure analysis

The analysis of the structure of the pectoralis major muscle is presented in Table 5. Japanese quails, regardless of gender, were characterized by a significantly (P < 0.001) larger cross-sectional area. However, male Japanese quails had larger vertical fiber diameters compared to male Pharaoh quails. It was also shown that the fiber circumference was larger in male Japanese quails compared to the analysed feature in females, while the analysed feature in Pharaoh quails was larger in females (P = 0.010). The same relationship was demonstrated when analysing vertical and horizontal fiber diameters between genotypes (P = 0.012; 0.028, respectively). Male Japanese quails were characterized by thicker connective tissue (perimisium) compared to the analysed feature in male Pharaoh quails (P = 0.001). However, in females we showed the opposite relationship when analysing the same feature. By examining the thickness of the connective tissue (perimisium) within the sexes, we showed a significantly thicker perimisium in male Pharaoh quails and Japanese quails compared to females within the same species. Interactions between genotype and gender were also found in the analysed features of the pectoral muscle structure (P < 0.001–0.003).

Table 5 Microstructural characteristics of pectoralis major muscle of Pharaoh and Japanese quails slaughtered at 6 weeks of age.
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Anatomical analysis

Table 6 presents data on the contents of the stomach, proventriculus, heart, liver and spleen depending on the genotype and sex of quails. There were significant (P < 0.05) differences in the percentage of proventriculus, heart and liver. Japanese quails were characterized by a significantly higher proportion of proventriculus, heart and liver compared to Pharaoh quails regardless of sex (P = 0.001–0.048). In the remaining analysed features (percentage of spleen and gizzard), we did not show statistically significant differences between genotypes and males and females (P = 0.087; 0.133, respectively).

Table 6 Percentage of selected internal organs in body weight of Pharaoh and Japanese quails slaughtered at 6 weeks of age.
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Table 7 presents data on the influence of quail genotype and sex on the lengths and diameters of intestinal segments. Pharaoh quails had significantly longer duodenum and colon regardless of sex (P < 0.001). The length of the caeca was higher in Pharaoh quails compared to the analysed feature in Japanese quails (P = 0.012). It was also not found significant (P > 0.05). The influence of genotype and sex on the length of the jejunum plus ileum and total intestine. Nevertheless, total intestine length was higher but not significant by an average of 5.28 cm in Pharaoh quails compared to the analysed feature in Japanese quails. The diameter of the duodenum, caeca and colon was significantly larger in Pharaoh quails compared to the analysed features in Japanese quails (P < 0.001–0.002). The duodenum diameter was larger in females compared to males regardless of genotype (P < 0.001). Also, the diameter of the caeca was larger in female than in males (P = 0.005). There was no interaction between genotype and gender in the analyzed characteristics of the length and diameter of individual intestinal sections (P = 0.098–0.941).

Table 7 Length and diameter of intestinal segments of Pharaoh and Japanese quails slaughtered at 6 weeks of age.
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Table 8 presents data on the dimensions of the femur and tibia of Japanese and pharaoh quails at the age of 42 days. Pharaoh quails were characterized by significantly greater measurements of the femoral segments GB, GD, SM, GC and GE (P = 0.001–0.034). Females were also characterized by higher GL and ML measurements of the femur compared to males (P = 0.001). When analyzing the dimensions of the tibia, Pharaoh quails were characterized by significantly higher GD, SB, SD and DD measurements compared to the analyzed features in Japanese quails (P < 0.001–0.007). However, it was also shown that Japanese quails were characterized by significantly larger AL and GL dimensions of the tibia (P = 0.027, 0.049; respectively). In turn, in females, a significantly larger GL dimension of the tibia was found compared to the analyzed feature in males (P = 0.047). Interactions between genotype and sex were also demonstrated in the analyzed features of Gl and ML of the femur and Gl and Al of the tibia (P = 0.011–0.037).

Table 8 Dimensions of the femur and tibia of Pharaoh and Japanese quails slaughtered at 6 weeks of age.
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Discussion

Many studies have shown that the carcass weight, slaughter yield and meat quality of quails are influenced by the genotype, age, sex, nutrition and housing system of the birds9,15,23,24,25,26. Kirrella et al.15 showed significant differences in body weight and carcass weight of birds depending on the colour of Japanese quail. Birds with brown plumage had significantly lower body weight compared to birds with white plumage. This study also found that bird genotype had an impact on body weight, carcass weight and the proportion of carcass elements in the carcass. Higher body weight, carcass weight and the percentage of skin with subcutaneous fat, neck and residue were observed in Pharaon quails, as they are characterized by a greater share of meat characteristics. In turn, Cullere et al.24 showed that the nutritional supplement used in the form of Camelina sativa dietary cake in the feeding of Japanese quails resulted in a deterioration of the carcass weight of the birds compared to the control group. The carcass weight results obtained in the above study (control—169.0 g) on day 35 were higher than the results in our study on day 42, regardless of the genotype (Pharaoh, females—116.8 g; Japanese, females—107.6 g). Abou-Kassem et al.9, analysing the effect of age on the composition of the carcass, showed significant differences between the percentage of breast and leg muscles in Japanese quails between 5 and 6 weeks of age. Birds at 6 weeks of age were characterized by a higher percentage of breast and leg muscles compared to birds at 5 weeks of age. The proportion of breast muscles (26.28%) and legs (18.65%) in Japanese quails regardless of sex in our study was higher than the results shown in the above study in Japanese quails of the same age (25.20%, 16.33%, respectively). In a study by Wilkanowska and Kokoszyński27 they reported that the percentage of neck and wings in the carcass was influenced by the age of the birds. Pharaoh quails on the 33rd day of life had a significantly (P < 0.05) higher percentage of analysed features compared to birds on the 42nd day. This study, however, showed that male Pharaoh quails had a higher percentage of necks and females had a higher percentage of wings compared to the analysed feature in the same sex in Japanese quails. Male Pharaoh quails in this study were characterized by the highest percentage of skin with subcutaneous fat (16.13%), however, the results obtained were lower than those obtained in another study (18.15%) in birds of the same genotype and age27.

The study by Abou-Kassem et al.9 showed that the age of the birds influenced the content of water, protein, fat and ash in the meat of Japanese quails. Birds aged 5 weeks were characterized by a higher proportion of water and ash, and lower protein and fat in the meat compared to the analysed characteristics of meat from birds aged 7 weeks. Other authors have shown that the water and fat content in the breast muscle was influenced by the diet24. The dietary supplement of Camelina sativa cake in the diet of Japanese quails increased the fat content and decreased the amount of water in the breast muscle compared to the control group24. Another study11 showed that bird age and origin influenced the content of water, fat, protein and ash in the breast muscle of Japanese quail. Meat (breast muscle) from birds aged 6 weeks had a higher water content and lower protein and fat content compared to the analysed characteristics of birds aged 8 months, while wild birds had a lower ash content and higher protein content compared to quails aged 6 weeks of life. Lukanov et al.28 reported that the basic chemical composition of the breast and leg muscles was influenced by the direction of use of Japanese quails. The breast muscles of birds used for meat purposes were characterized by a lower percentage of dry matter and intramuscular fat and a higher percentage of protein compared to the analysed characteristics of birds used for laying purposes. In turn, the leg muscles of Japanese quails (meat type) contained less dry matter and less intramuscular fat in relation to the analysed characteristics of laying quails. In our research, we confirmed this relationship, because Pharaon quails, which have meat characteristics, had a higher fat and water content in the breast and leg muscles compared to Japanese quails. Moreover, it was also observed that the breast and leg muscles of females contained more water and less fat compared to the analyzed features in males.

This study also found that the colour characteristics (L⃰ and b⃰) of the pectoralis major muscle were influenced by the genotype of the birds. The pectoral muscles of Japanese quails had significantly (P < 0.05) higher brightness values compared to the analysed feature of Pharaoh quails. Most likely, the darker color of the breast muscles of pharaoh quails was influenced by the genotype of the birds, because in the past pharaoh quails were selected based on meat characteristics. Another study showed that the colour of the pectoral muscle was influenced by the age of the birds. In males, the pectoral muscle became more red with age, while in females it was significantly less yellow29. This relationship was also confirmed in another study9, which showed that the L⃰ colour saturation decreased with the age of Japanese quails, while the a⃰ colour saturation increased. Another study12 also showed that the colour (L⃰, a⃰, b⃰) of the breast muscle was influenced by the slaughter age of Japanese quails. The pectoral muscle of females had higher redness (a*) with the age of the birds, while the brightness (L⃰) decreased, while the pectoral muscle of males had higher yellowness (b⃰) with age. The results of yellowness of the pectoral muscle in Japanese quails obtained by Varol Avcilar and Yilmaz29 at the 4th week of life were at a similar level to the results obtained in this study in birds of the same genotype, while the redness in our study was higher by 6.04 in males and by 8.02 in females at compared to birds from 8 weeks of age. Gümüş30 pointed out that the dietary supplement of 0.5% sodium bentonite resulted in greater redness of the breast muscle of Japanese quails compared to the control group.

The texture of meat (tenderness, rubberiness, hardness) is influenced by many factors, including breed, gender, nutrition, chemical composition, structure of muscle fibers, and pre-slaughter stress17. Meat tenderness mainly depends on collagen content and maturity, the type of muscle fibers, the diameter of intramuscular fat and the degree of proteolysis in stiff muscles26. A study by Varol Avcilar and Yilmaz29 showed that age (4–8 weeks of age) and sex in Japanese quails had no effect on the texture parameters of the pectoral muscle. In another study, it was shown that the texture characteristics (tenderness, chewiness, gumminess, elasticity) pectoralis major muscle was influenced by the age of the birds (native chickens, laying hens)31,32, the maintenance system of the parent flocks of meat hens and the genotype of the birds (Ross 308 v Cobb 500)17. This study also found the influence of the quail genotype on the cutting work, hardness, elasticity, chewiness and gumminess of the breast muscle. The higher values of texture features observed in Pharaoh quails were influenced by the structure of the pectoral muscle, in particular perimysium thickness and fiber perimeter, which were significantly higher in Pharaoh quails. Moreover, in our study, the influence of bird sex on the elasticity of the pectoral muscle of Japanese quails. The pectoral muscles of females had higher elasticity compared to the analysed feature in males. Another study26 showed a negative effect of a nutritional supplement in the form of mulberry leaf pulp (100 g/1 kg) on the shear force of the breast muscle; the additive used increased the value of the analysed feature, which indicates greater hardness of the meat.

Balowski et al.33 reported that the species has a significant impact on the analysed features of the pectoral muscle structure. Japanese quails were characterized by a pectoral muscle with the smallest fiber cross-sectional area compared to other bird species (pheasant, goose, duck, partridge, guinea fowl). The same authors33 also found that the pectoral muscles of pheasant, goose and duck had thicker connective tissue (perimysium and endomysium) compared to Japanese quail, which has a significant impact on muscle hardness. The area of intramuscular fat in the Japanese quail was comparable to the area of the pigeon and partridge, but much smaller compared to the analysed feature in the pheasant, goose, duck and guinea fowl. In this study, the pectoral muscles of Pharaoh quails were characterized by a smaller cross-sectional area and vertical fiber diameter, and a thicker perimysium compared to the analyzed features in Japanese quails. Most likely, the meat characteristics of Pharaoh quails that were selected in the past resulted in lower values of the structure (fiber cross-sectional area, fiber diameter V) of the breast muscle. The remaining analysed structural features, i.e. fiber circumference, horizontal fiber diameter (H), vertical fiber diameter (V), perimysium and endomysium thickness, were influenced by the sex of the birds. Males had thicker perimysium, endomysium and vertical and horizontal fiber diameters compared to females.

Many studies have shown that the percentage and weight of offal (heart, liver, stomach, forestomach) were influenced by nutrition, feed consumption, gender and age of the birds9,15,25,30,34. The study by Kirrell et al.15 showed that females had a higher liver weight than males, regardless of the colour of Japanese quails at 6 weeks of age. However, in another study9, the age of the birds influenced the liver percentage. The authors showed that liver percentage was highest in birds at 6 weeks of age compared to 5 and 7 weeks. In this study, the birds' genotype significantly differentiated them in terms of the percentage of liver. Japanese quails were characterized by a significantly higher percentage of liver in relation to the analysed feature in Pharaoh quails, regardless of gender. However, the results obtained in this study were 0.41% lower than the results obtained in another study in Japanese quails of the same age9. Mutter and Abbas25, using a feed additive in the form of potato peel powder (15 g/1 kg) to feed Japanese quails, showed an increase in the percentage of liver and heart compared to the control group. In this study, the percentage of body weight of the heart and proventriculus was influenced by the genotype of the birds. Pharaoh quails were characterized by a lower percentage of analysed traits compared to Japanese quails, regardless of gender. Another study showed that the percentage of proventriculus was influenced by the diet30. Gümüş30 showed that the percentage of proventriculus increased with the amount of sodium bentonite supplement used. The heart rate obtained in our study was at a similar level compared to the results in other studies9,30.

This study showed that the bird genotype influenced some lengths of intestinal segments (duodenum, caeca, colon). Pharaoh quails had longer duodenum, caeca, and colon compared to the analysed features of Japanese quails. The results obtained in this study duodenum (9.57 cm) in Japanese quails at 6 weeks of age were lower, compared to the analysed feature (13.72 cm) in Japanese quails at 8 weeks of age34. The study by Wilkanowska et al.35 showed that the age of Pharaoh quails did not significantly affect the length of the entire intestine, but 42-day-old quails had shorter intestines (78.70 cm) compared to the intestines of Pharaoh quails (85.93 cm) in this study in birds in same age. In the same study35, the authors found lower caeca and colon lengths in Pharaoh quails at week 6 (15.9 cm, 5.7 cm) compared to the results obtained in this study in birds of the same origin and age (17.46 cm; 7.34 cm, respectively). The study by Kirrell et al.15 showed the influence of genotype and gender on the weight of the gastrointestinal tract. Female Japanese quails with white plumage were characterized by a heavier digestive tract compared to female Japanese quails with brown plumage at the 4th week of life, while at the 6th week of life, regardless of the genotype, females had a heavier digestive tract compared to males. The study by Wilkanowska et al.35 showed that Pharaoh quails on the 33rd day were characterized by a higher intestinal to body length ratio compared to birds from the 42nd day.

The study by Kirrell et al.15 showed that the length of the tibia was significantly longer in female Japanese quails with white plumage compared to males with brown plumage. Lee et al.36 reported that the length and width of the tibia in Japanese quail at 4 months of age were affected by the myostatin mutation (MSTN) used. Mutant quails in which myostatin mutations were used during rearing were characterized by longer and wider tibiae compared to the analysed features in wild Japanese quails. Other studies have shown that the length of the tibia in Japanese quails was influenced by the breeding line37. The heaviest quails from the breeding line (selected for body weight) were characterized by the longest tibia lengths in relation to the analysed feature in the lightest and unselected quails. In this study, some femur and tibia lengths were influenced by bird genotype and sex. Pharaoh quails were characterized by longer GB, GD, SM, GC and GE segments of the femur and GD, SB, SD and DD of the tibia. However, females were characterized by longer GL and ML sections of the femur and GL of the tibia compared to males. The higher measurements of individual features of the femur and tibia in Pharaoh quails in our study were most likely influenced by the initial higher body weight. Greater body weight also resulted in greater measurements of tibia and femoral bone characteristics in females.

To sum up, it can be said that in terms of carcass weight, Pharaoh quails were the better genotype, while Japanese quails were characterized by greater musculature (breast and leg muscles) and the percentage of offal (heart, proventriculus, liver). In terms of meat quality, Japanese quails were characterized by lighter and more springiness meat, with lower water content and higher fat content, while the breast meat of Pharaoh quails was darker, harder and more gumminess, characterized by a smaller fiber cross-sectional area. Pharaoh quails are characterized by a longer digestive tract, especially the duodenum and colon. However, the greatest depth of the proximal end (GD) and greatest breadth of the distal end (GC) of the femur and greatest diagonal of the proximal end (GD) of the tibia were higher in Pharaoh quails. Regardless of genotype, male quails had lower body weight, carcass weight and a higher percentage of skin with subcutaneous fat compared to female quails. Male quails also had darker, lower springiness pectoral muscle, which furthermore had bigger muscle fibre diameters and connective tissue thicknesses. In addition, male quails were found to have lower water content in pectoral and leg muscles and higher fat content in pectoral muscles than female quails. Limitations of this study include the relatively small size of the study material. This was mainly related to the time-consuming nature of measuring biometric traits of the digestive tract, femur and tibia bones, and especially the determination of microstructural traits of m. pectoralis major of the compared breeds of Japanese quail. In the case of leg muscles, the small size of the acquired samples made it impossible to determine their physicochemical characteristics, texture and microstructure using the applied research methods. However, the results obtained provided abundant and valuable information on carcass composition and meat quality of Japanese quail (C. coturnix japonica) useful for quail meat consumers, nutritionists, food technologists. These results were slow to determine the suitability of carcasses and meat of compared breeds of quail with different directions of use (Japanese quails—egg production type and Pharaoh quails—meat type) for culinary purposes. In turn, the results of studies on the evaluation of biometric traits of the digestive system, leg bones (femur and tibia) complement the knowledge of quail anatomy. This article presents, for the first time, results on the effect of the genotype of Japanese quails with different directions of use on meat microstructure and texture traits (except WB shear force), as well as leg bone dimensions.