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.
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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.
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FACTORS
THAT INFLUENCE HATCHABILITY
(INTRINSIC AND EXTRINSIC FACTORS)
1.
TEMPERATURE
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).
2. TURNING CONDITION
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.
3.
STORAGE TIME
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).
4.
EGG QUALITY
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.
4.
NUTRITION
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.
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EFFECT
OF BREEDER AGE ON HATCHABILITY
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).
EFFECT
OF EGG SIZE ON HATCHABILITY
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).
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HOW
TO IMPROVE THE HATCHABILITY OF EGG
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.
CONCLUSION
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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