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).
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