Review Article
Siedlce University of Natural Sciences and Humanities, Institute of Animal Sciences and Fisheries, Prusa 14, 08-110 Siedlce, Poland
Abstract. Hatching results depend on the biological value of the eggs and on factors affecting the development of the embryo during incubation, as well as the conditions in which the eggs are kept between being laid and being placed in the incubator. Numerous studies conducted in Poland and other countries indicate that the suitability of eggs for hatching and their biological value are determined by genetic factors (mainly the origin of the birds) as well as environmental factors. Hatching eggs are primarily subject to assessment of external characteristics. The most important characteristics determining whether eggs are suitable for incubation are their weight, shape, structure and eggshell condition, as proper structure is a fundamental condition of satisfactory hatching results. Egg weight is highly dependent on genetic factors, as evidenced by the high heritability coefficients of this trait. Assessment of the hatching eggs weight is important because the weight of the hatchling is positively correlated with the egg weight. Works clearly confirm the effect of genotype on the physicochemical features of eggs, including the weight of the egg, yolk and eggshell. The eggshell plays an extremely important role in eggs used for reproduction. Eggshell quality traits are determined by both genotype and non-genetic factors, including the layer hen age and the diet, particularly the amount, form and availability of calcium. An important factor affecting the hatching process and quality of chicks is egg storage.
Keywords: structure, egg quality, hatching, genetic factors
Eggs intended for hatching are obtained from poultry breeding flocks, and the requirements for these eggs are much higher than for table eggs. Hatching results depend on the biological value of the eggs and on factors affecting the development of the embryo during incubation, as well as the conditions in which the eggs are kept between being laid and being placed in the incubator. Numerous studies conducted in Poland and other countries indicate that the suitability of eggs for hatching and their biological value are determined by genetic factors (mainly the origin of the birds) as well as environmental factors [Spiller et al. 2003Spiller, S.V., Varga, S., Kovacs, M.L., Kozak, J. (2003). Effect of parents, age and hatching egg weight in liver production geese. Arch. Geflügelkunde, 67(5), 237–239. Google Scholar, Boruta and Pijarska 2004Boruta, A., Pijarska, I. (2004). Ocena morfologiczna jakości jaj wylęgowych pochodzących z podwójnej owulacji [Morphological assessment of the quality of hatching eggs from double ovulation]. Zesz. Nauk. Prz. Hod., 73, 103–117 [in Polish]. Google Scholar, Gierzilov 2004Gierzilov, V. (2004). Relationship of semen traits of one and two-year-old Muscovy drakes. Zhivot. Nauki, 41(20), 28–32. Google Scholar, Tilki and Inal 2004Tilki, M., Inal, S. (2004). Field traits of geese of different origins reared in Turkey hatching. Türk Veterinerlikve Hayvancilik Dergisi, 28(1), 149–155. Google Scholar, Malec 2005Malec, H. (2005). Monitorowanie jakości skorup jaj kurzych w ocenie dobrostanu niosek [Monitoring the quality of chicken egg shells in assessment of the welfare of laying hens]. Zesz. Nauk. PTZ. Prz. Hod., 3, 1–6 [in Polish]. Google Scholar, Biesiada-Drzazga 2009Biesiada-Drzazga, B. (2009). Estimation of morphological composition and physical traits of hatching eggs in the selected meat hen stocks. Rocz. Nauk. PTZ, 5, 1, 35–42. Google Scholar]. Embryonic development and hatching results depend on both the external and internal characteristics of hatching eggs. The physical characteristics of eggs and the value of individual features of their structure are adapted to the fundamental biological function of the egg, i.e. proper development of the embryo in specific environmental conditions [Węsierska 2006Węsierska, E. (2006). Czynniki jakości mikrobiologicznej spożywczych jaj kurzych [Factors of microbiological quality of chicken eggs]. Med. Weter., 62(11), 1222–1228 [in Polish]. Google Scholar, Onagbesan et al. 2007Onagbesan, O., Bruggeman, V., De Smit, L., Debonne, M., Witters, A., Tona, K., Everaert, N., Decuypere, E. (2007). Gas exchange during storage and incubation of Avian eggs: effects on embryogenesis, hatchability, chick quality and post-hatch growth. Worl's Poult. Sci. J., 63, 557–573. https://doi.org/10.1017/S0043933907001614]. Hatching eggs are primarily subject to assessment of external characteristics. The most important characteristics determining whether eggs are suitable for incubation are their weight, egg shape, structure and eggshell condition, as proper structure is a fundamental condition of satisfactory hatching results.
As early as the 1980s and 1990s, research was carried out on the effect of the egg weight and egg shape index on hatching rates [e.g. Szczerbińska 1997Szczerbińska, D. (1997). Ocena jaj kur nieśnych żywionych mieszanką paszową z udziałem wywaru gorzelnianego [Assement of eggs laying hens fed compound feed with stillage]. Med. Weter., 63(1), 99–103 [in Polish]. Google Scholar, Christensen et al. 2001Christensen, V.L., Grimes, J.L., Wineland, M.J. (2001). Effects of turkey breeder hen age, strain, and length of the incubation period on survival of embryos and hatchlings. J. Appl. Poult. Res., 10, 5–15. https://doi.org/10.1093/japr/10.1.5, Biesiada-Drzazga and Janocha 2009Biesiada-Drzazga, B., Janocha, A. (2009). Wpływ pochodzenia i systemu utrzymania kur na jakość jaj spożywczych [Impact of the origin and housing system of chickens on the quality of table eggs]. Żywn. Nauka Technol. Jakość, 3(64), 67–74 [in Polish]. Google Scholar]. In addition, Pijarska [2005]Pijarska, I. (2005). Od czego zależy jakość lężonych obecnie piskląt? [What determines the quality of chicks from contemporary hatcheries?]. Pol. Drob., 6, 19–22 [in Polish]. Google Scholar, Rachwał [Rachwał 2008aRachwał, A. (2008a). Wpływ warunków środowiska i czasu przechowywania jaj na rozwój zarodków i jakość wylężonych piskląt, cz.I [Impact of enviromental conditions and egg storage time on embryo development and quality of hatched chicks, part I]. Pol. Drob., 5, 20–22 [in Polish]. Google Scholar, Rachwał 2011Rachwał, A. (2011). Zwiększenie efektywności hodowli kur mięsnych, cz. V [Increasing the efficiency of breeding meat hens, part V]. Pol. Drob., 9, 18–21 [in Polish]. Google Scholar] and Reijrink et al. [2008]Reijrink, I.A.M., Meijerhof, R., Kemp, B., Van Den Brand., H. (2008). The chicken embryo and its micro environment during egg storage and early incubation. World's Poult. Sci. J., 64(4), 581–598. https://doi.org/10.1017/S0043933908000214 studied the effect of egg weight on the weight of hatchlings, showing a significant impact of this trait on hatching of healthy chicks. The generally accepted measure of egg size is their weight. Egg weight is highly dependent on genetic factors, as evidenced by the high heritability coefficients of this trait (h2 = 0.4–0.6) for various populations of chickens [Zhang et al. 2005Zhang, L.C., Ning, Z.H., Xu, G.Y., Hou, Z.C., Yang, N. (2005). Heritabilities and genetic and phenotypic correlations of egg quality traits in brown-egg dwarf layers. Poult. Sci., 84, 1209–1213. https://doi.org/10.1093/ps/84.8.1209].
Nys [2000]Nys, Y. (2000). Dietary carotenoids and egg yolk coloration – a review. Arch. Geflugelk., 64(2), 45–54. Google Scholar emphasizes that egg weight depends on genetic (h2 = 0.4–0.6) and environmental factors, mainly temperature and diet. The egg size is affected by the age and weight of the hen. Egg weight is primarily determined by the weight of the albumen, and to a lesser extent by the yolk and eggshell [Bednarczyk 1991Bednarczyk, M. (1991). Wpływ czynników dziedzicznych oraz warunków środowiskowych chowu kur na jakość jaj [Impact of hereditary factors and environmental conditions of chicken farming on egg quality]. Zesz. Nauk. Drob., Rozpr. 29, Pozn. [in Polish]. Google Scholar]. Many studies have shown that the best hatching results are obtained from medium-weight eggs. Eggs of inappropriate weight usually have an abnormal yolk-to-white ratio. Water can also evaporate more easily from small eggs, leading to excessive density of their contents and impeding nutrient absorption by the embryo.
Assessment of the weight of hatching eggs is important because the weight of the hatchling is positively correlated with the egg weight. The effect of egg weight on hatchling weight has been demonstrated in other experiments [Yannakopoulos and Tserveni-Gousi 1987Yannakopoulos, A., Tserveni-Gousi, A. (1987). Effect of breeder quail age and egg weight on chick weight. Poult. Sci., 66, 1558–1560. https://doi.org/10.3382/ps.0661558, Pijarska 2005Pijarska, I. (2005). Od czego zależy jakość lężonych obecnie piskląt? [What determines the quality of chicks from contemporary hatcheries?]. Pol. Drob., 6, 19–22 [in Polish]. Google Scholar].
Yolk weight is a crucial factor affecting hatchability. In heavier eggs, the share of yolk may be smaller than in eggs of low or medium weight, which can negatively affect embryonic development [Huse and Kuźniacka 2015Huse, H., Kuźniacka, J. (2015). Czynniki wpływające na efektywność lęgu jaj różnych gatunków ptaków [Factors affecting the hatching efficiency of eggs of various bird species]. Wiad. Drob., 5(6), 17–23 [in Polish]. Google Scholar]. Any change in the proportions of the morphological components of the egg (eggshell, white and yolk) can reduce hatching rates [Michalak and Mróz 2003Michalak, K., Mróz, E. (2003). Jakość białka jaja [Egg white quality]. Pol. Drob., 4, 9–10 [in Polish]. Google Scholar].
The egg weight is determined more by the body weight of the bird than by its laying capacity. The relationship between egg weight and the body weight of the layer is primarily a function of the secretory capacity of the oviduct magnum, which in turn depends on the surface area of the oviduct [Bednarczyk 1991Bednarczyk, M. (1991). Wpływ czynników dziedzicznych oraz warunków środowiskowych chowu kur na jakość jaj [Impact of hereditary factors and environmental conditions of chicken farming on egg quality]. Zesz. Nauk. Drob., Rozpr. 29, Pozn. [in Polish]. Google Scholar]. Another feature affecting egg weight is the laying rate, which determines the time the egg is in the oviduct. Increased egg weight and size are associated with the ongoing growth of the bird and development of its reproductive system, and mainly with the increased rate of oocyte growth and albumen secretion in the magnum [Adamski 2008Adamski, M. (2008). Zależności między składem morfologicznym jaj a wylęgowością piskląt wybranych gatunków ptaków [Relationships between the morphological composition of eggs and hatchability of chicks of selected bird species]. Rozpr. UTP Bydg. 130 [in Polish]. Google Scholar]. Laid eggs may be very small, below 48 g, or very large, above 73 g. Very small eggs may appear when the birds first begin laying, indicating that the flock is not sufficiently mature. Large eggs weighing over 73 g may have two yolks. Double-yolk eggs are formed when two ovarian follicles burst simultaneously in the ovary and two yolks fall into the oviduct. They are then surrounded by a common albumen layer and eggshell. Sokołowicz and Krawczyk [2004]Sokołowicz, Z., Krawczyk, J. (2004). Wpływ wieku kur i wielkości obsady na jakość jaj spożywczych [Impact of hen age and stocking density on table egg quality]. Rocz. Nauk. Zoot., 31(1), 103–113 [in Polish]. Google Scholar have shown that one of the factors influencing egg weight is the laying rate. A lower laying rate allows birds to store more of the material needed to build and increase egg weight. Calik [2002]Calik, J. (2002). Kształtowanie się zależności między masą ciała kury a masą jaja [Relationships between hen body weight and egg weight]. Zesz. Nauk. Prz. Hod., 61, 71–72 [in Polish]. Google Scholar, analysing the relationship between egg weight and body weight of hens from strains H33, M55 and V44, confirmed the close relationship between body weight and egg weight, as reduced weight of layers was accompanied by a decrease in egg weight, and conversely, heavier hens usually laid heavier eggs.
The shape of hatching eggs, defined by the egg shape index, is significant, as proper egg shape is a condition for normal development of embryos and chicks during incubation. Better hatching rates are widely believed to be obtained from round eggs. Research by Pakulska et al. [2003]Pakulska, E., Badowski, J., Bielińska, H., Bednarczyk, M. (2003). Wpływ wieku na cechy fizyczne jaj i wylęgowość piskląt gęsi białych kołudzkich [Impact of age on the physical characteristics of eggs and hatchability of White Kołuda geese chicks]. Zesz. Nauk. Prz. Hod., 68(4), 71–77 [in Polish]. Google Scholar showed better fertilization and hatching rates from more rounded goose eggs.
According to Szczerbińska [1997]Szczerbińska, D. (1997). Ocena jaj kur nieśnych żywionych mieszanką paszową z udziałem wywaru gorzelnianego [Assement of eggs laying hens fed compound feed with stillage]. Med. Weter., 63(1), 99–103 [in Polish]. Google Scholar, the egg shape affects hatching rates because it determines the positioning of the embryo. Deterioration in hatching occurs when the egg shape index significantly deviates from the average for the species. The author states that elongated, flattened or spherical eggs pose a problem when they are placed on the incubator tray. In the case of spherical eggs it can be difficult to determine which is the blunt end, so they may be placed in the incubator with the air cell facing downward, thus reducing the chance of hatching. In elongated eggs, on the other hand, the embryo may be incorrectly positioned when it shifts from a horizontal to a vertical position.
In addition to the weight and shape of eggs, hatching rates also depend largely on the quality characteristics of eggs, including their morphological composition [Kuchida et al. 1999Kuchida, K., Fukaya, M., Miyoshi, S., Suzuki, M., Tsuruta, S. (1999). Nondestructive prediction method for yolk: Albumen ratio in chicken eggs by computer image analysis. Poult. Sci., 78, 909–913. https://doi.org/10.1093/ps/78.6.909]. The egg of all species consists of the same basic components, in a characteristic layered arrangement [Huse and Kuźniacka 2015Huse, H., Kuźniacka, J. (2015). Czynniki wpływające na efektywność lęgu jaj różnych gatunków ptaków [Factors affecting the hatching efficiency of eggs of various bird species]. Wiad. Drob., 5(6), 17–23 [in Polish]. Google Scholar]. Studies of the morphological components and physical characteristics of eggs are relatively numerous [Silversides and Scott 2001Silversides, F.G., Scott, T.A. (2001). Effect of storage and layer age on quality of eggs from two lines of hens. Poult. Sci., 80(8), 1240–1245. https://doi.org/10.1093/ps/80.8.1240, Suk and Park 2001Suk, Y.O., Park, C. (2001). Effect of breed and age of hens on the yolk to albumen ratio in two different genetic stocks. Poult. Sci., 80(7), 855–858. https://doi.org/10.1093/ps/80.7.855, Abanikannda and Leigh 2007Abanikannda, O.T.F., Leigh, A.O. (2007). Allometric relationships between composition and size of chicken table eggs. Int. J. Poult. Sci, 6(3), 211–217. https://doi.org/10.3923/ijps.2007.211.217, Abanikannda et al. 2007Abanikannda, O.T.F., Olutogun, O., Leigh, A.O., Ajayi, L.A. (2007). Statistical modeling of egg weight and egg dimensions in commercial layers. Int. J. Poult. Sci., 6(1), 59–63. https://doi.org/10.3923/ijps.2007.59.63]. Works by Silversides and Budgell [2004]Silversides, F.G., Budgell, K. (2004). The relationships among measures of egg albumen height, pH and whipping volume. Poult. Sci., 83, 1619–1623. https://doi.org/10.1093/ps/83.10.1619 and by Czaja and Gornowicz [2006]Czaja, L., Gornowicz, E. (2006). Wpływ genomu oraz wieku kur na jakość jaj spożywczych [Impact of the genome and age of hens on the quality of table eggs]. Rocz. Nauk. Zoot., 33(1), 59–70 [in Polish]. Google Scholar clearly confirm the effect of genotype on the physicochemical features of eggs, including the weight of the egg, yolk and eggshell. Narushin and Romanov [2002]Narushin, V.G., Romanov, M.N. (2002). Egg physical characteristics and hatchability. World's Poult. Sci. J., 58(3), 297–303. https://doi.org/10.1079/WPS20020023, Hocking et al. [2003]Hocking, P.M., Bain, M., Channing, C.E., Fleming, R., Wilson, S. (2003). Genetic variation for egg production, egg quality and bone strength in selected and traditional breeds of laying fowl. Br. J. Poultr. Sci., 44(3), 365–373. https://doi.org/10.1080/0007166031000085535, Basmacioglu and Ergul [2005]Basmacioglu, H., Ergul, M. (2005). Characteristic of egg in laying hens. The effect of genotype and rearing system. Turk. J. Vet. Anim. Sci., 29, 157–164. Google Scholar, Czaja and Gornowicz [2006]Czaja, L., Gornowicz, E. (2006). Wpływ genomu oraz wieku kur na jakość jaj spożywczych [Impact of the genome and age of hens on the quality of table eggs]. Rocz. Nauk. Zoot., 33(1), 59–70 [in Polish]. Google Scholar, Krawczyk [2009]Krawczyk, J. (2009). Effect of layer age and egg production level on changes in quality traits of eggs from hens of conservation breeds and commercial hybrids. Ann. Anim. Sci., 9(2), 185–193. Google Scholar, have also shown that genotype influences egg quality.
The shell plays an extremely important role in eggs used for reproduction. Eggshell quality traits are determined by both genotype and non-genetic factors, including the age of the layer and the diet, particularly the amount, form and availability of calcium [Scott and Silversides 2000Scott, T.A., Silversides, F.G. (2000). The effect of storage and strain of hen on egg quality. Poult. Sci., 79, 1725–1729. https://doi.org/10.1093/ps/79.12.1725, Silversides and Scott 2001Silversides, F.G., Scott, T.A. (2001). Effect of storage and layer age on quality of eggs from two lines of hens. Poult. Sci., 80(8), 1240–1245. https://doi.org/10.1093/ps/80.8.1240]. Calik [2011]Calik, J. (2011). Ocena jakości jaj sześciu rodów kur nieśnych w zależności od ich wieku [Assessment of egg quality of six strains of laying hens depending on their age]. Żywn. Nauka Technol. Jakość, 5(78), 85–93 [in Polish]. Google Scholar, in an assessment of the quality of eggs of six strains of laying hens, also found that the origin and age of hens affected the quality features of eggs and their shells. Hocking et al. [2003]Hocking, P.M., Bain, M., Channing, C.E., Fleming, R., Wilson, S. (2003). Genetic variation for egg production, egg quality and bone strength in selected and traditional breeds of laying fowl. Br. J. Poultr. Sci., 44(3), 365–373. https://doi.org/10.1080/0007166031000085535, Roberts [2004]Roberts, J.R. (2004). Factors affecting egg internal quality and egg shell quality in laying hens. J. Poult. Sci., 41(3), 161–177. https://doi.org/10.2141/jpsa.41.161, Biesiada-Drzazga and Janocha [2009]Biesiada-Drzazga, B., Janocha, A. (2009). Wpływ pochodzenia i systemu utrzymania kur na jakość jaj spożywczych [Impact of the origin and housing system of chickens on the quality of table eggs]. Żywn. Nauka Technol. Jakość, 3(64), 67–74 [in Polish]. Google Scholar, and Krawczyk [2009]Krawczyk, J. (2009). Effect of layer age and egg production level on changes in quality traits of eggs from hens of conservation breeds and commercial hybrids. Ann. Anim. Sci., 9(2), 185–193. Google Scholar have emphasized that the feature most correlated with the hen’s genotype is the eggshell colour, whose intensity depends on age.
The eggshell performs a fundamental function in gas exchange, protecting the developing embryo, and supplying it with calcium to build the skeleton. The eggshell protects the contents of the egg against both penetration by harmful microorganisms from the outside and evaporation of water from the inside. From the moment the egg is laid, physicochemical changes referred to as ageing lead to a loss of the natural protective capacity of the eggshell and the movement of water and gases, both within the contents of the egg and between its internal environment and the surrounding environment . The amount of water that evaporates from the inside of the egg is determined by physiological factors, such as the permeability of the shell, the diameter of the eggshell pores, and the rate at which the cuticle dries out and cracks. Small eggs, with a greater surface area in relation to their volume, have been shown to lose water faster [Calik et al. 2003Calik, J., Połtowicz, K., Wężyk, S. (2003). Wpływ systemu utrzymania kur nieśnych oraz warunków przechowywania jaj spożywczych na ich jakość [Impact of the housing system of laying hens and storage conditions of table eggs on their quality]. Wydaw. Inst. Zootech., Kraków, 57–62 [in Polish]. Google Scholar].
The path to the inside of the egg leads through the eggshell pores, which number from 7000 to 17,000, with a diameter from 13 microns at the blunt end to 6 microns at the pointed end [Węsierska 2006Węsierska, E. (2006). Czynniki jakości mikrobiologicznej spożywczych jaj kurzych [Factors of microbiological quality of chicken eggs]. Med. Weter., 62(11), 1222–1228 [in Polish]. Google Scholar]. Shell quality is also determined by its ultrastructure. Studies on the ultrastructure of the eggshell and eggshell membranes have been conducted by Carnarius et al. [1995]Carnarius, K.M., Conrad, K.M., Mast, M.G., Mac Neil, J.H. (1995). Relationship of eggshell ultrastructure and shell strength to the soundness of shell eggs. Poult. Sci., 75, 656–663. https://doi.org/10.3382/ps.0750656 in chicken eggs, by Puchajda et al. [1997]Puchajda, H., Cywa-Benko, K., Faruga, A., Pudyszak, K., Mróz, E. (1997). Porównanie budowy makroskopowej ultrastruktury skorup jaj indyków różnego pochodzenia [Comparison of the macroscopic egg shell ultrastructure of turkeys of various origins]. Rocz. Nauk. Zoot., 24(1), 34–43 [in Polish]. Google Scholar in turkey eggs and by Puchajda et al. [2000]Puchajda, H., Pudyszak, K., Mróz, E., Cywa-Benko, K. (2000). Ultrastruktura skorup i budowa makroskopowa jaj gęsi białych kołudzkich i biłgorajskich [Shell ultrastructure and macroscopic structure of the eggs of Kołuda and Biłgoraj geese]. Rocz. Nauk. Zoot., 27(1), 65–78 [in Polish]. Google Scholar in goose eggs. According to these researchers, hatching of chicks is more influenced by the ultrastructure of the shell than by its thickness. Hatching results are also affected by the structure of the pores of the eggshell [Meir and Ar 1987Meir, M., Ar, A. (1987). Improving turkey poult quality by correcting incubator humidity to match eggshell conductance. Br. J. Poultr. Sci., 28, 337–342. https://doi.org/10.1080/00071668708416966, Tullet 1990Tullet, S.G. (1990). Science and art of incubation. Poult. Sci., 69, 1–15. https://doi.org/10.3382/ps.0690001].
According to some authors, the thickness of the chicken eggshell ranges from 0.25 to 0.45 mm and varies over the surface of the shell. It is thickest at the pointed end of the egg, intermediate at the blunt end, and thinnest at the equator. According to other researchers [Malec et al. 1999Malec, H., Borzemska, W., Niedziółka, J. (1999). Zmiany w strukturze przekroju skorupy jaja u niosek chorych na kolibakteriozę [Changes in the structure of the egg shell cross-section in layers suffering from colibacteriosis]. Med. Weter., 55(4), 268–271 [in Polish]. Google Scholar], eggshell thickness is genetically determined, but can be influenced by environmental factors. This opinion is supported by the research of numerous authors [Shafey 2002Shafey, T.M. (2002). Effects of egg size and eggshell conductance on hatchability traits of meat and layer breeders flocks. Asian Austral. J. Anim. Sci., 15(1), 1–6. https://doi.org/10.5713/ajas.2002.1, Nowak and Sobczak 2005Nowak, A., Sobczak, J. (2005). Systemy utrzymania kur nieśnych a jakość konsumencka skorup jaj [Housing systems of laying hens and consumer quality of egg shells]. Prz. Hod., 74(1), 1–4 [in Polish]. Google Scholar, Biesiada-Drzazga and Janocha 2009Biesiada-Drzazga, B., Janocha, A. (2009). Wpływ pochodzenia i systemu utrzymania kur na jakość jaj spożywczych [Impact of the origin and housing system of chickens on the quality of table eggs]. Żywn. Nauka Technol. Jakość, 3(64), 67–74 [in Polish]. Google Scholar]. In a study by Puchajda et al. [2000]Puchajda, H., Pudyszak, K., Mróz, E., Cywa-Benko, K. (2000). Ultrastruktura skorup i budowa makroskopowa jaj gęsi białych kołudzkich i biłgorajskich [Shell ultrastructure and macroscopic structure of the eggs of Kołuda and Biłgoraj geese]. Rocz. Nauk. Zoot., 27(1), 65–78 [in Polish]. Google Scholar, the average eggshell thickness of two-year-old White Koluda geese was 0.530 mm at the pointed end of the egg, 0.515 mm at the blunt end, and 0.547 mm in the middle. Dohnal et al. [1990]Dohnal, J.M., Kiełczewski K., Łakota P., Pośpiech, M. (1990). Ubytek masy jaj w wyniku parowania jako wskaźnik oceny jakości skorupy [Egg weight loss due to evaporation as an indicator of shell quality]. Zesz. Nauk. Drob., 7, 41–50 [in Polish]. Google Scholar indicated a relationship between the hatching rate and the thickness and strength of the eggshell. The eggshell thickness was found to be inversely proportional to the ability of water vapour to pass through it.
The weight, density and elastic deformation of the shell affect the quality of the incubation and hatching processes [Gornowicz et al. 2013Gornowicz, E., Węglarzy K., Szablewski, T. (2013). Jakość skorupy jaj pozyskanych metodami ekologicznymi [Quality of shells of eggs obtained by organic methods]. Wiad. Zootech., 51(4), 19–30 [in Polish]. Google Scholar]. Fragile shells, which are subject to microcracks, allow bacteria and fungi abundant in the henhouse environment to penetrate the egg [Mertens et al. 2006Mertens, K., Bamelis, F., Kemps, B., Kamers,B., Verhoelst, B., Ketelaere, B., De Bain, M., Decuypere, E., De Baerdemaeker, J. (2006). Monitoring of eggshell breakage and eggshell strength in different production chains of consumption eggs. Poult. Sci., 85(9), 1670–1677. https://doi.org/10.1093/ps/85.9.1670]. Results reported by Premavalli and Viswanagthan [2004]Premavalli, K., Viswanagthan, K. (2004). Influence of age on the egg quality characteristics of commercial white leghorn chicken. Indian J. Vet., 81(11), 1243–1247. Google Scholar indicate a positive relationship between the strength, thickness, and density of the eggshell. The authors found that the age of hens affects the frequency of internal cracks in the eggshell and that egg weight is negatively correlated with eggshell thickness. On the other hand, according to Pantheleux et al. [1999]Pantheleux, M., Bain, M., Fernandez, M.S., Morales, I., Gautron, J., Arials, J.L., Solomon, S.E., Hincke, M., Nys, Y. (1999). Organic matrix composition and ultrastructure of eggshell: a comparative study. Br. Poultry. Sci., 40, 240–252. https://doi.org/10.1080/00071669987665, a thicker eggshell is only partially responsible for greater strength. Hunton [2005]Hunton, P. (2005). Research on eggshell structure and quality: An historical overview. Braz. J. Poultr. Sci., 7, 67–71. https://doi.org/10.1590/S1516-635X2005000200001 emphasizes that the mechanical properties of the eggshell are primarily influenced by its structure and the concentration of matrix proteins, and the changes in the mechanical properties of the eggshell that take place with age are associated with a reduction in the hen’s absorption of calcium and phosphorus from feed and slower mineralization.
The yolk is the largest known biological cell. It is a concentrate of essential vitamins, minerals, and fatty acids with valuable biological properties. Research by Kontecka et al. [2012]Kontecka, H., Nowaczewski, S., Sierszuła, M.M., Witkiewicz, K. (2012). Analysis of changes quality of broiler breeders during the first reproduction period. Ann. Anim. Sci., 12(4), 609–620. https://doi.org/10.2478/v10220-012-0051-1 indicates an increase in yolk weight in successive weeks of laying in Cobb 500 flocks, accompanied by deterioration in its quality.
The albumen plays an extremely important role in the hatching egg. Egg albumen consists mainly of colloidal proteins, with a small amount of sugars and mineral salts. Studies have shown that an increased proportion of albumen in the egg negatively affects hatching results. According to Huse and Kuźniacka [2015]Huse, H., Kuźniacka, J. (2015). Czynniki wpływające na efektywność lęgu jaj różnych gatunków ptaków [Factors affecting the hatching efficiency of eggs of various bird species]. Wiad. Drob., 5(6), 17–23 [in Polish]. Google Scholar, in chicken eggs with 63% albumen the hatching rate from fertilized eggs (89.5%) is higher than for eggs with 53% albumen, in which the hatching rate from fertilized eggs is only 66.1%. The time eggs are stored before being placed in the incubator also has a major impact on deterioration of albumen quality. Storage of eggs lowers the pH of the albumen, adversely affecting its quality and loosening its structure [Michalak and Mróz 2003Michalak, K., Mróz, E. (2003). Jakość białka jaja [Egg white quality]. Pol. Drob., 4, 9–10 [in Polish]. Google Scholar].
In egg production by breeding flocks of chickens, while the number of eggs obtained from the layer is of course important, the primary task is to obtain eggs that can be used for hatching. Cocks are widely believed to be responsible for egg fertilization, although some influence of the hens should be considered as well. Poor fertilization rates can result from overweight cocks and their associated low sexual activity, from damage to their feet and the skin on the soles due to poor litter quality, or from an inadequate male-to-female ratio in the flock [Rachwał 2011Rachwał, A. (2011). Zwiększenie efektywności hodowli kur mięsnych, cz. V [Increasing the efficiency of breeding meat hens, part V]. Pol. Drob., 9, 18–21 [in Polish]. Google Scholar]. Fertilization results depend on semen quality, the reproductive behaviour of females, the mating system, diet, and environmental conditions, including day length. The substantial impact of environmental factors is due to the low heritability of this trait. Research by Goncalves et al. [2015]Goncalves, F.M., Santos, V.L., Farina, G., Oliveira, C.O., Anciuti, M.A., Rutz, F. (2015). Nutritional aspects and reproductive management of roosters in Brazil. World's Poult. Sci. J., 71, 515–521. https://doi.org/10.1017/S0043933915002238 confirms that reproduction results depend to a very great extent on cocks. Therefore, males should not be selected for the breeding flock solely on the basis of body weight and conformation traits; an assessment of semen quality is necessary as well. It should be emphasized that studies on reproduction are particularly justified in meat hens. Breeding birds of this type often attain high body weight, which makes it difficult to obtain high fertilization rates in natural mating, especially in the second half of the reproductive period [Gumułka et al. 2003Gumułka, M., Kapkowska, E., Rapacz, J.M. (2003). Wartość wybranych wskaźników płodności kur mięsnych po zastosowaniu inseminacji [Values of selected fertility parameters of meat hens after artificial insemination]. Zesz. Nauk. Prz. Hod., 68(4), 95–101 [in Polish]. Google Scholar]. Artificial insemination is currently used on a large scale in meat chickens with the dwarfism gene (dw). In breeding practice, however, it may become a necessity in all meat hens.
A characteristic feature of reproduction in birds is the ability of females to store sperm in the oviduct, which enables the use of economically beneficial natural mating of several females with one male in poultry farming, as well as artificial insemination. The likelihood that consecutively laid eggs will be fertilized, taking into account polyspermy in birds, depends in part on the number of sperm present in the infundibulum. It can be roughly estimated based on the sperm population retained in the perivitelline layer in laid eggs. Gumułka and Kapkowska [2002]Gumułka, M., Kapkowska, E. (2002). Próba określenia wpływu wieku kur mięsnych na liczbę plemników zatrzymanych w warstwie pozażółtkowej jaj [An attempt to determine the effect of the age of meat hens age on the number of sperm retained in the perivitelline layer of eggs]. Zesz. Nauk. Prz. Hod., 61, 54–55 [in Polish]. Google Scholar, in a study conducted on eggs obtained from Arbor Acres meat hens, showed a marked decrease in the number of sperm stored in old hens (62 weeks old compared to 36 weeks old).
An important factor affecting the hatching process and quality of chicks is egg storage. Studies on the eggs of laying hens and meat hens have investigated the impact of egg storage time on their quality [Silversides and Scott 2001Silversides, F.G., Scott, T.A. (2001). Effect of storage and layer age on quality of eggs from two lines of hens. Poult. Sci., 80(8), 1240–1245. https://doi.org/10.1093/ps/80.8.1240, Suk and Park 2001Suk, Y.O., Park, C. (2001). Effect of breed and age of hens on the yolk to albumen ratio in two different genetic stocks. Poult. Sci., 80(7), 855–858. https://doi.org/10.1093/ps/80.7.855] and incubation conditions [Barbosa et al. 2013Barbosa, V.M., Rocha, J.S.R., Pompeu, M.A., Martins, N.R.S., Baiao, N.C., Lara, L.J.C., Batista, J.V.M.S.P., Leite, R.C. (2013). The effects of relative humidity and turning in incubators machines on the incubation yield and chick performance. Worl's Poultr. Sci. J., 69, 89–97. https://doi.org/10.1017/S0043933913000081, Bergoug et al. 2013Bergoug, H., Burel, C., Guinebretiere, M., Tong, Q., Roulston, N., Romanini, C.E.B., Exadaktylos, V., Mcgonnell, I.M., Demmers, T.G.M., Verhelst, R., Bahr, C., Berckmans, D., Eterradossi N. (2013). Effect of pre-incubation and incubation conditions on hatchability, hatch time and hatch window, and effect of post-hatch handling on chick quality at placement. Worl's Poultr. Sci. J., 69, 313–334. https://doi.org/10.1017/S0043933913000329]. According to Pijarska and Malec [2006]Pijarska, I., Malec, H. (2006). Przygotowywanie jaj wylęgowych do inkubacji [Preparation of hatching eggs for incubation]. Pol. Drob., 4, 20–22 [in Polish]. Google Scholar, eggs are not suitable for incubation immediately after they are laid. The best results are obtained from eggs stored for 3–4 days before being placed in the incubator. This is the time required for stabilization of egg structures, primarily the albumen and chalaza, for the loose fibres of the inner eggshell membrane to become compact, and for completion of eggshell calcification [Pijarska and Malec 2006Pijarska, I., Malec, H. (2006). Przygotowywanie jaj wylęgowych do inkubacji [Preparation of hatching eggs for incubation]. Pol. Drob., 4, 20–22 [in Polish]. Google Scholar]. On the other hand, a number of changes occur when eggs are stored for too long, such as cracking of the cuticle, an increase in the pH of the egg contents, water evaporation, air cell enlargement, thinning of the yolk, weakening of the vitelline membrane, protein breakdown, loss of vitamins and lysozyme, and accumulation of toxins due to embryo development. Chicks from such eggs have a lower body weight and may have poorer health and survival rates.
According to Rachwał [2008aRachwał, A. (2008a). Wpływ warunków środowiska i czasu przechowywania jaj na rozwój zarodków i jakość wylężonych piskląt, cz.I [Impact of enviromental conditions and egg storage time on embryo development and quality of hatched chicks, part I]. Pol. Drob., 5, 20–22 [in Polish]. Google Scholar, 2008bRachwał, A. (2008b). Wpływ warunków środowiska i czasu przechowywania jaj na rozwój zarodków i jakość wylężonych piskląt, cz.II [Impact of enviromental conditions and egg storage time on embryo development and quality of hatched chicks, part II]. Pol. Drob., 6, 12–14 [in Polish]. Google Scholar, 2008cRachwał, A. (2008c). Wartość odżywcza paszy a wylęgowość jaj [Nutritional value of feed and hatchability of eggs]. Pol. Drob., 9, 11–14 [in Polish]. Google Scholar], egg storage conditions should ensure that the embryos are not damaged or weakened, which reduces hatching results. Incubation of chicken eggs that have been stored too long prolongs the incubation period, due to delayed embryo development and slower growth in the first days of incubation. According to the author, in chickens the negative impact of prolonged egg storage time on hatching results depends on the age of the flock and the origin of the birds. The research showed that only eggs from younger flocks can be stored for more than one week. In eggs from one line of Lohmann Brown hens stored up to nine days, hatchability of over 85% was obtained, while in the case of another Lohmann Brown line it fell to below 80% after seven days of storage. In addition, the study reported the highest hatchability not from completely fresh eggs, but from eggs that had been stored for 3–4 days.
With regard to storage conditions for hatching eggs, it should be noted that the egg itself has a number of defense mechanisms that protect it against adverse environmental conditions, mainly penetration by microorganisms. These include the following:
According to Węsierska [2006]Węsierska, E. (2006). Czynniki jakości mikrobiologicznej spożywczych jaj kurzych [Factors of microbiological quality of chicken eggs]. Med. Weter., 62(11), 1222–1228 [in Polish]. Google Scholar, the egg is particularly vulnerable to penetration by microbes during laying and the formation of an oxygen reservoir for the developing embryo. The natural protection of eggs by the inner and outer eggshell membrane lasts 14 days or more, but only in optimal microclimate conditions [Chowdhury 1990Chowdhury, S.D. (1990). Shell membrane protein system In relation to lathyrogen toxicity and copper deficiency. World's Poultr. Sci. J., 46, 620–631. https://doi.org/10.1079/WPS19900018] .
The main factors inhibiting microbial proliferation in eggs are widely believed to be the lack of available nutrients in the albumen and its highly alkaline pH [Węsierska 2006Węsierska, E. (2006). Czynniki jakości mikrobiologicznej spożywczych jaj kurzych [Factors of microbiological quality of chicken eggs]. Med. Weter., 62(11), 1222–1228 [in Polish]. Google Scholar]. An important role is played by ovotransferrin, also called conalbumin, which has the ability to bind iron, copper or aluminium ions, owing to which it exhibits bacteriostatic activity. Another substance with a major role is lysozyme, which has high enzymatic activity (e.g. hydrolysis of the cell walls of Gram-positive bacteria) and forms a complex with ovomucin, responsible for the gelatinous structure of egg white. Cystatin and avidin present in egg white are also highly bactericidal, with the ability to bind biotin, which is necessary for the growth and development of many microorganisms [Que and Reed 2000Que, X., Reed, S.L. (2000). Cysteine proteinases and the pathogenesis of amebiasis. Clin. Microbiol. Rev., 13, 196–206. https://doi.org/10.1128/CMR.13.2.196, Węsierska et al. 2005Węsierska, E., Saleh, Y., Trziszka, T., Kopeć, W., Siewiński, M., Korzekwa, K. (2005). Actimicrobial activity of chicken egg white cystatin. World J. Microbiol. Biotechnol., 21, 59–64. https://doi.org/10.1007/s11274-004-1932-y, Węsierska 2006Węsierska, E. (2006). Czynniki jakości mikrobiologicznej spożywczych jaj kurzych [Factors of microbiological quality of chicken eggs]. Med. Weter., 62(11), 1222–1228 [in Polish]. Google Scholar].
Numerous studies conducted in Poland and other countries indicate that the suitability of eggs for hatching and their biological value are determined by genetic factors (mainly the origin of the birds) as well as environmental Hatching eggs are primarily subject to assessment of external characteristics. The most important characteristics determining whether eggs are suitable for incubation are their weight, shape, structure and eggshell condition, as proper structure is a fundamental condition of satisfactory hatching.
This study was financed by the funds of the Ministry of Science and Higher Education of Poland (statutory research fund of the Siedlce University of Natural Sciences and Humanities No 55/20/B).
Received: 15 Apr 2020
Accepted: 20 Jun 2020
Published online: 21 Jul 2020
Accesses: 1260
Biesiada-Drzazga, B., (2020). Evaluation of eggs in terms of hatching capability. Acta Sci. Pol. Zootechnica, 19(2), 11–18. DOI: 10.21005/asp.2020.19.2.02.
