Table 2 shows the albumen, yolk, shell, fluid and embryo rates in the different periods of incubation in the eggs of Chukar partridges. These rates were determined to be 53.62, 34.84, 11.53, 0.0 and 0.0% on the day 0 (fresh egg), 16.47, 33.49, 16.22, 31.76 and 2.06% on day 7, 15.65, 28.32, 15.58, 23.35 and 17.10% on day 14 and 0.0, 23.33, 19.38, 0.0 and 57.29% on day 21 of incubation, respectively. The shell ratio on the hatching day (24
th) was 8.41% and the mean chick weight was 16.16 g (72.04%). The proportional values of the fresh egg components are compatible with the other studies
(Song et al., 2000; Alkan et al., 2015; Kirikçi et al., 2018). However, no previous information was available on the changes in egg components during incubation. In the following periods of incubation, the decrease in albumen and fluid was remarkable.
Moran (2007) states that the embryo uses albumen and yolk through the vitelline membrane for 14 days of its development and consumes albumen and amniotic-allantoic fluid mixture by oral route after day 14. Similarly, it was determined in the present study that both egg components were finished on day 21 of incubation. The egg weight change was similar in the examined periods of incubation (~3-4%) and the growth rate of the embryo varied during incubation and increased significantly towards the end of incubation mostly between days 14 and 21 (Table 2).
Table 3 shows the proportional values of the nutrient components of the egg in different periods of incubation. When examined weekly, the moisture content of yolk increased in the first week and then decreased. It could be related that the increase in the yolk’s moisture level in the first week was associated with the fluid and electrolyte flow from the fluid and albumen due to the osmolarity difference between the egg components
(Uni et al., 2012). Another reason for the increase in the moisture level of the yolk is thought to be the lipids hydrolyzed during the use of yolk through a vitelline membrane
(Maatjens et al., 2014; Sheng, 2014). The crude protein content of yolk decreased until the last week of incubation. It increased significantly in the last week. The crude fat content of yolk increased significantly in the third week and decreased in the last week. While its carbohydrate level increased in the last week, its crude ash content decreased in egg yolk. The energy level of the yolk was calculated to be high in the first and third weeks and low in the second and the fourth weeks. Embryo growing rapidly during incubation that used all the nutrients in egg yolk. The fluctuation was observed in the crude protein and fat contents and the carbohydrate level increased significantly towards the end of incubation. The reason for the fluctuations in the crude protein and fat rates of the yolk was the proteins coming from the albumen and the fluid. The previous studies revealed that it was also caused by the proteins and lipids releasing as a result of the degradation of the yolk sac
(Yadgary et al., 2010). Uni et al., (2012) determined that the lipid consumption of yolk increased towards the end of incubation, which was similar to the results of this study. It was determined that the significant increase of the carbohydrates in yolk was associated significantly with carbohydrate synthesis in the egg performed to provide the energy needed by the embryo while being prepared for hatching day.
Yadgary and Uni (2012) stated that gene expression levels of glycogen synthase, glycogen phosphorylase, gluconeogenic enzymes fructose 1,6-bisphosphatase, phosphoenolpyruvate carboxykinase and glucose 6-phosphatase increased significantly in the liver of embryo in this period. Table 3 also shows the nutrient content of albumen in the first three measurements. The moisture content of albumen decreased significantly from the first measurement; whereas, the crude protein and ash content increased. The carbohydrate level did not change. The crude fat and energy level increased in the first week and decreased again in the third week. The moisture and carbohydrate contents did not change in the fluid that can be collected in the first and the second weeks of incubation. While crude protein and ash content of the fluid increased, its crude fat and energy level decreased. The crude ash content of the shell decreased significantly in the first week and the differences in the crude ash content were not statistically significant in the following weeks.
Table 4 shows the nutritional changes of the egg components in the different periods of incubation. The carbohydrate content of yolk decreased between days 0 and 7 and its moisture content increased. The change of the other nutrients was similar. The carbohydrates of egg yolk were consumed mostly between days 8 and 14, its crude fat and energy level increased and the other nutrients reduced gradually. The carbohydrate content of yolk between days 15 and 21 increased significantly, its protein content increased and the reducing change of the other nutrients was similar. It was determined that all the nutrients in yolk were consumed gradually between days 0 and 21. While the highest change was observed in the carbohydrate content, the lowest change was observed in the energy level and the decreases in the moisture, crude protein, fat and ash contents were statistically similar. The energy, crude fat and crude protein contents of albumen increased significantly between days 0 and 7, respectively and the moisture, carbohydrate and crude ash contents decreased similarly. The crude fat content of albumen decreased mostly between days 8 and 14, which was followed by moisture, ash, carbohydrate, protein and energy. The energy and crude protein contents of albumen increased significantly between days 0 and 14 and the moisture, carbohydrate, crude ash and fat contents decreased. The crude protein and ash contents of the fluid increased between days 8 and 14 and the crude fat, crude ash, energy and moisture contents decreased significantly. The crude ash change in eggshell on the days 0 and 24 were found to be -60.03± 1.14%. Similarly,
Yair and Uni (2011) stated that yolk was rich in Mn, P, Fe, Ca, Cu and Zn and the mineral consumption of yolk was low at the beginning and increased mostly between days 11 and 17 of incubation and then decreased again. The crude ash consumption of yolk was determined to be the highest on days 15 and 21 of incubation in the present study. The studies generally focused on the nutrient composition of yolk and a limited number of studies on the nutrient change in the other parts of the egg were found. When the nutrient change of albumen in the various periods of incubation was examined (Table 4), the moisture level of albumen decreased significantly in the first week and the concentration relatively continued in the other period. The crude protein and fat level of albumen increased in the first week, then decreased in the second week and had a value less than the initial amount. It was considered that the increase in the protein and fat amount of albumen in the first week of incubation was caused by the demand of these matters to pass to the less concentrated environment from the high concentrated environment and the difference in the osmotic pressure
(Uni et al., 2012). The fact that the color of albumen became yellowish at the end of the first week may be an important indicator of the passage of some matters caused especially by yolk. The ash and carbohydrate level of albumen decreased continuously and proportionally as of the beginning. The energy of albumen increased in the first week and was relatively lower in the second week. This increase in the energy of albumen was caused by the increase of the crude protein and fat content of albumen in the first week. The fact that the ash and carbohydrate amount of albumen continuously decreased proportionally corresponds to the information that albumen is an important source of Na, K and carbohydrate of the embryo
(Uni et al., 2012). In the examination of fluid, the moisture content of the fluid decreased on days 8 and 14. The crude protein content of the fluid increased on days 8 and 14. The crude fat, carbohydrate and energy rates of the fluid decreased among the examined periods. The crude protein and ash increase in the fluid is considered to indicate that the embryo starts to form uric acid crystals in the urinary system in this period. It was thought that the protein amount in the fluid increases as it is known that uric acid crystals are present in association with urate monosodium salt or proteins and the protein amount was found by calculating the N number in the present study (
Stower and Bertocchini, 2017). The fact that the crude ash amount in the eggshell was significantly lower than the initial value corresponds to the information that it is used as a source of phosphor, sodium, iron and manganese and three is high amounts of calcium, magnesium and sulfur required for feeding of the embryo
(Uni et al., 2012). It was considered that the increase in the ash level of the shell between the days 0-14 and 0-21 was because the chorio-allantoic membrane covers the inner membrane of the eggshell and it becomes thick. The crude ash analyses of eggshells were performed in the membranous eggshell.