The monitoring of egg quality
characteristics is important mainly in terms of production economy. The
attention is devoted especially to egg shell quality because cracked egg shell
present higher losses for market egg producers. Therefore it is very important
to evaluate the egg quality characteristics and the factors affecting than. The
genotype is one of the most important factors influencing not only the weight
but also other egg characteristics.
The genotypes affect mainly egg weight
and shell characteristics. The size of eggs is commonly expressed in terms of
weight, which provide a more convenient basis of comparison than dimension, or
volume. Egg normally weigh from 40 to
80g each. The highest recorded chicken egg weight was 320g, the smallest was 1.3g
(Zhang et al., 2005)
The average gross composition (by
weight) of hen’s egg is about 10 percent shell, 30 percent yolk, and 60 percent
albumen. Large egg contain
proportionally more albumen and less yolk than small ones. The percentage of
the shell remains nearly constant, except than the first pullet eggs contain
relatively more shell and less yolk than small ones in characteristics of hen
in general. A medium size hen producing 300 eggs annually deposits about 3.751b
of calcium carbonate in the egg shells. This represents about three times the
amount of calcium in her entire body and point to the need for an abundance of
calcium in her feed
Present evidence indicate that only
about 60 percent of the calcium in a particular egg comes directing from the feed
(Tumova et al., 1993). The balance
comes form deposits in the long bones. In
a wild birds that lays only a few eggs, all the
calcium may come from bones. However, when laying hens are suddenly deprived of
all feed calcium, their eggs promptly show thin shell and the hen stops laying in 10 to 14 days. Of all the egg components,
the shell is the most variable, shell decrease about 25 percent when the hen environmental temperature was
increased form 60 t0250f (19 to 300C). The albumen also
decreased significantly whereas the yolk weight remained about constant.
Several studies have shown heavier
eggs in brown hens than in white ones (Arent et al., 1997) reported a significant effect of age on egg weight in
leghorn type hens. Egg weight influences the weight of it’s component as well.
The correlations between the egg weight and the albumen weight, yolk weight,
egg shell weight are high and ranges from 0.67 to 0.97 (Zhang et al., 2005). Harms I, (1990) reported
the range of correlation between the egg size and shell thickness as 0.92 to
0.97. The egg shape index in the white hen shaver star cross 288 was higher
than in the brown Moravia SSt (Halaj and Grofik, 1994).
The effect of strain on yolk and albumen quality
characteristics was observable by Tumova et
al., (1993). They found significantly higher yolk weight and percentage in
Hisex Brown in brown eggs than in D-29 with white eggs. In contrast,
Leyendecker et al., 200ib) showed
significantly higher yolk weight in white egg chickens. (lohmann LSL) in
comparison with the brown lohmann tradition. Heritability in yolk weight is
0.45 (Zhang et al., 2005), 0.22
(Hartmann et al., 2000). From the
albumen quality characteristics only Haugh unit were influenced by genotype
(Tumova et al., 2007), (Leyendecker et al., 200lb) found significantly
higher value in Haugh unit in white layers than in brown hens. (Zhang et al., 2005). Showed that heritability
of Haugh units is 0.41 and for albumen weight 0.59. However, Hartmann et al., 2000) found 0.4 for albumen
weight. The correlation between yolk percentage and yolk weight was 0.52 where
as the correlations with egg weight and albumen weight were – 0.51 and -0.74,
respectively (Hartmann et al., 2000).
With higher egg weight, the average albumen percentage increased (Arent et al., 1997). The genotype
significantly affected the yolk index (Tumova et al., 2007).
The egg quality is given through it’s
weight and percentage of eggshell, thickness and strength. The main difference
in egg quality depend on the way of breeding strains or pure lines. Egg weight
directly effected the egg size and shell thickness. For instant brown hens has
a higher shell weight in comparison with line of white leghorn (Ledvinka et al., 2000). Main difference in egg
shell quality were between the white and brown hens. Brown eggs had thicker egg
shell than the White ones. (Ledvinka et al., 2000),(Haiaj and Grofik, 1994)
and leyendecker et al ., 2001b) found
a thinner shell in brown eggs.
Egg shell deformation was 35.7mm in brown eggs
and 32.6mm in white. Significantly higher negative correlation among egg shell
deformation and egg shell strength and thickness was found in brown eggs
compared to white eggs. (Halaj and Grofik 1994), but in the other hand, in
white eggs these correlations were on slightly negative. Non significance
difference in shell strength were determined by (Tumova et al., 2007) invariable brown strains. However higher shell
strength was reveled in white egg chicken (Halj and Grofik, 1994), (Ledvinka et
al., 2000). Heritability of eggshell weight is 0.64, eggshell chickens o.34 and
egg shell strength 0.24 (Zhang et al.,
2005).