The term hatch-ability is described as the percentage of eggs surviving to the time of hatching that produce a chick. An egg failing to hatch is a considerable energetic loss to the bird that laid it as well as to those that incubated it. The avian egg is a biological system intended to ensure the well-being of embryo and it’s successful hatching into a fully developed chick (Narushin and Romanov, 2002).
Predictable reproductive performance of parent stock as essential for every commercial hatchery to produce as many sellable chicks at the lowest possible cost, and uniform chicks set the basis for a successful rearing and subsequent production. The problem of hatchability of eggs is one of many complications. The more usual conception of the term does not take this fact into consideration. In studies on hatchability, instead of considering the single incident-the emergence of the chick from the shell-it should be kept in mind that  large number of physiological process are concerned.



             In reality many factors, can affect hatchability especially egg size and the life span of the bird from fertilization to the emergence of the chick from the egg, season of the year and nutrition, egg handling, storage, temperature and humidity through the incubation and hatching period (Wilson 1997). Reproductive traits decline with increasing age toward the end of the laying cycle. The decrease of hatchability in order flocks is well-know and may be explained as a result of lower fertility of male and female, but probably more important is the reduction in eggshell quality with increasing egg weight. Bamelis (2003) Suggested that low hatchability of fertile eggs at the beginning of the breeding season and the decline in hatchability with increasing age is also due to improper egg water loss.       Although commercial hatcheries avoid prolonged storage of hatching egg, sometime there is no other option to fill large orders. Tona et al., (2003) concluded that long egg storage time increase incubation duration, which affect negatively the quality of the chicks.
            Eggs of exotic birds and common chickens require a standard measure of care in storage and incubation to ensure a successful hatch. Environmental conditions, handling, sanitation and record keeping can impact the success of incubating and hatching eggs. Most eggs are laid by mid-morning. Eggs should be collected several times a day to reduce the amount of time egg remain in the nest. This practice decreases the number of cracked and soiled eggs and also prevent premature incubation. Embryos begin to prematurely develop at temperature above 72 degree 0F., starting and stopping embryo development by repeatedly changing temperature increase, embryo death. Frequent collection and proper storage delays embryo development until egg incubation can begin. However, hatchability is affected by age of parent flock, genetic, egg weight, and egg storage. Older flocks tend to have the poorest hatchability (Lapao, 1999). It has also been found that as the length of storage increase hatchability decrease (Lapao, 1999). Breed and Line of the same breed differ in reproductive traits, but relatively little within-Line selection has been practiced for hatchability in commercial breeding programs focused on efficiency of egg production of the final cross (flock, 1995). Egg characteristic greatly influence the process of incubation and are responsible for its success (Narushin and Romanov, 2002). The egg shell has an important role during embryonic development, isolating the embryo from the external environment while allowing the proper gas exchange through the shell. Barnett et al. (2004) reported that eggs with hairs-cracks showed increase bacterial exposure and weight loss, with significantly lower hatchability (56.4% Vs. 80.9%) compared with thin and thick shells based on specific gravity measurements and reported a reduction in hatchability of 3 to 9%, which he attributed to increased cracks, moisture loss and bacterial contamination of eggs with thin shells.
            Frequent statement have been incorporated in the literature on poultry as to the influence of certain factor on hatchability. Some of these are well supported by experimental evidence, while in many other instances, the evidence is very inadequate.


The optimum operating temperature for poultry species during incubation appear to be from 37 to 38oC. Incubation temperature is not only important for normal embryonic development and hatching success but also affect post hatch performance. It is recommended that incubation temperature is adapted to the natural heat production pattern of the incubating egg to obtain the highest hatchability with good-quality chicks. A recent publication of Lourens et al., (2005) showed that the highest hatchability, embryo development and post hatch performance was found when eggshell temperature was maintained at 37.8oc constantly through incubation. Mortality is seen if the temperature drops bellow  35.6Oc or rises above 39.4oc for a number of hours (Kingiori, 2011).

Egg turning has been reported to reduce malpositions, to prevent abnormal adhesion of embryo or embryonic membranes to the shell membrane, to encourage the complete and timely closure of chorioallantois at the small end of the egg, and most importantly, is needed to achieve an optimal albumen utilization by the embryo (Deeming, 2002; Tona et al., 2005). Insufficient turning during incubation leads to a delay of hatching and adversely affect day-old chick qualitative aspects. Tona et al., (2003c) found that  hatchability and percentage of high quality chicks were lower for egg, turned for 15 day compared with those turned for 12 or 18 day (day 15 is in the period of an increasing functional hypothalamus-pituitary-adrenal axis). Tona1 et al. (2005) hypothesized that discontinuation of turning at this time may be an additional stressor that can lead to physiological imprinting and altered responsiveness, leading to lower hatchability and chick quality.

Hatching egg can be successfully stored for up to 7 days with little or no effect on hatchability. However, when stored for more than 1 week, embryonic abnormalities and mortality increase, which cause a decline in hatchability; moreover, incubation time is delayed when eggs are stored for a longer time.
            Long-term egg storage as known to affect general egg quality (Yolk membranes, yolk, perivitelline layers).   The incidence of more abnormal and dead embryos may be related to a higher number of embryonic cells with necrotic nuclei and an increase in number of apoptotic cells (Cells programmed to die) as a result of storage. The initiation of embryonic development is delayed, which could be brought into relation with the delay in hatching time. This delay is seen in a later occurrence of the start of internal pipping (IP) and a prolonged IP stage (Tona et al., 2003b). Moreover, the rate of embryonic development is lower due to longer storage, but this phenomenm is not observed for all embryos, indicating that not all embryo are affected by storage in the same way (Dasenko et al., 2002).

The overall quality of an egg can be discussed under two broad categories namely “external” and “Internal” quality (Manira  et al., 2003). The external quality of the egg is determined by features such as the size and shape of the egg as well as the structure, thickness  and strength of the shell(Bain, 2005). The internal quality is measured on the basis of the quality of the albumen as indicated by the Haugh units (HU), the relative size of the various internal components, and the integrity of the shell membrane. Several studies have looked at these egg quality assessment in chickens (Tona et al., 2002; de De Ketelaere et al., 2004; Bain 2005) as well as change in the micro environment provided by the egg during storage and early incubation and how these affect hatchability (Narushin and Romnov, 2002; Tona et al., 2002; reijriuk et al., 2008). This implies that egg quality was important in hatchability and can make substantial contribution to the genetic improvement of hatchability.

In the management of breeder poultry, feed is regulated to prevent excessive weight gain, a major cause of poor quality ejaculate and ovulation and at extremes , early ovarian and testicular regression (Brilland, 2007). This will ensure production of good quality and number of eggs and semen. However egg weight and yolk decreased in hens offered diets containing more than 5% CLA (Conjugated linoleic Acid). The dietary CLA caused adverse effects on hatchability when included in low fat diets. Ayidin et al. (2001) show that a CLA level of 0.5% in the diet caused complete embryonic mortality in fertile chicken eggs. Adeyemo et al. (2007) reported that cotton seed meal should not replace more than 50% of soya bean meal in breeder cock diet because gossypol suppresses sperm production.


            It is well known that incubating egg weight and therefore day-old chick weight at hatch depends on the age of the breeder. Similarly, Hill (2001) reported an increase in chick length with increasing age of the breeder. The incidence of chicks of hatching eggs of older breeders (Tona et al., 2001,. Boerjan, 2002; Tona et al., 2004a). Fresh egg from young breeders have better albumen quality hatch better, and produce higher percentages of high-quality 1-day-old chicks, although with lower weight at hatch but with a higher post hatch growth rate compared with older breeder (Tona et al., 2004a). Embryonic body and organ growth are highly conserved biological traits and embryos may regulate physiologically between growths and function when presented with life-threating situation (Christensen et al., 2002). The age effect could be reversed by moulting the breeders, lead to an improvement of hatchability and chick quality in terms of growth performance (Tona et al., 2002). 

Under normal circumstances, a fertile egg contains all the nutrients necessary for the development of the embryo to hatching. However, there are certain physical and chemical conditions of the egg that may lower or cause no hatchability at all. There may be due to environmental factors. The physical characteristics of the egg play an important role in the processes of embryo development and successful hatching (Narushin and Romanov, 2002). The most influential egg parameter are: weight, shell thickness and porosity, shape index (Described a maximum breadth to length ratio).
            Hatchability for small eggs (Asuquo and Okon, 1993). Egg size affects hatchability. Egg with 45-56g weight hatch better than lighter eggs. Best hatchability (97%) was reported for medium size eggs (50g) of Anak broiler egg (Abiola et al., 2008). Large egg (60g) has the lowest hatchability (83%). As egg size increase, yolk size increase’s more than the quality of albumen (North and Bell, 1990).

            To support hatchery management in producing high quality chicks within a reduced hatch window even from older flocks or prolonged egg storage, primary breeders select families with persistent hatchability under thesecondition (Forster 1994). As Decuypere and Bruggeman (2007) pointed out, the spread of hatch varies due to pre-incubation factors (e.g age of parent flock duration, temperature during egg storage, egg turning, the gaseous environment) all these effects should be known and taken into account.

Hatchability is a complex phenomenon influenced by a variety of ecological, geographical, and social variables. Genetic variation in hatchability of a fertile egg however, arises mostly from the dam which laid the eggs. This significant effect of the dam is attributed to the quality (external and internal) of the laid eggs which affect successful development of the embryo to a chick during incubation and the emergence of the chick form the egg at hatching.


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