الفهرس 
Introduction
Role and importance of local breeds in Egyptian poultry productionOnly 14 pages are availabe for public view
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Abstract
- SUMMARY AND CONCLUSION
The present study was carried out at the Poultry Farm of Poultry Production Department, Faculty of Agriculture, Assiut University, through two successive generation from October 2016 to March 2019.
This study aimed to determine the effect of selection for body weight at eight weeks of age on some productive traits such as growth measurements, carcass traits, egg production traits and egg quality traits in Dandarawi chickens. The study involved 2932 pedigreed chicks obtained by mating 96 sires with 935 dams through two successive generation. The chicks in each generation were divided into two lines, line (S) selected for high body weight and line (C) is control line.
The results obtained in this study could be summarized as follow:
1. Growth measurements:
1.1. Body weight: The differences between generation considering body weight were highly significant (P≤0.01) at 0, 4, 8 and 20 weeks of age but were not significant at 12 and 16 weeks of age. There were highly significant differences (P≤0.01) between line in body weight from 0 to 20 weeks of age and the selected line had heavier body weight than the control line over generation. The selected line had heavier body weight than the control line at 0, 4, 8, 12, 16 and 20 weeks of age. As for the effect of sex on body weight, it was highly significant (P≤0.01) from 4 to 20 weeks of age and males body weight from 4 to 20 weeks of age were heavier than that of females in the two line over generation. It was noticed that males and females in the selected line were heavier than their corresponding birds in the control line in all generation. There were highly significant (P≤0.01) interaction between generation and line at 0, 8, 12, 16 and 20 weeks of age. However, at 4 weeks of age it was not significant. There were significant (P≤0.01) interaction between generation and sex at 0 and 4 weeks of age but at 8, 12, 16 and 20 weeks of age were not significant. There were highly and significant (P≤0.01 and P≤0.05) interaction between line and sex at 4, 12 and 16 weeks of age but at 0, 8 and 20 weeks of age were not significant. There were highly significant (P≤0.01) interaction between generation and line and sex at 8, 16 and 20 weeks, but at 0, 4 and 12 weeks of age were not significant for body weight.
1.2. Sexual dimorphism: It was noticed that males body weight of both lines was heavier than those of the females for both line within the same age or at the different ages; males body weight in selected line were heavier than that males body weight in the control line over generation. The difference between males and females body weight in selected line was more than their corresponding values in control line over generation. Differences between the two sex (sexual dimorphism) were gradually increased from 4 to 20 weeks of age and the sexual dimorphism in selected line ranged from 16.1% to 38.83%, while in control line it ranged from 12.59% to 36.82% from 4 to 16 weeks of age, respectively.
1.3. Phenotypic gain due to selection for body weight at 8 weeks of age: It was noticed inconsistent increments in body weight where it was 1.19, 19.74, 17.66, 74.42, 79.43 and 125.87 g in first generation, while in the second generation it was 2.05, 15.35, 70.52, 162.86, 170.28 and 170.13 g at 0, 4, 8, 12, 16 and 20 weeks of age, respectively.
2. Body conformation:
2.1. Shank length at different ages (SL): Differences between generations it was highly significant (P≤0.01) at 4, 8, 12, 16 and 20 weeks of age. There were highly significant differences (P≤0.01) due to effect of line on shank length from 4 to 20 weeks of age and the selected line had longer shank length than the control line over generation. The selected line was longer in shank length when compared with control line at 4, 8, 12, 16 and 20 weeks of age. As for the effect of sex on shank length the results showed that males shank length from 4 to 20 weeks of age were longer than that of females in the two line over generation. It was noticed that males and females in the selected line showed longer shank length than those of the control line for all generation. The difference between sex in shank length was highly significant (P≤0.01) from 4 to 20 weeks of age. There were highly significant (P≤0.01) interaction between generation and line at 4, 12, 16 and 20 weeks of age, but at 8 weeks of age was not significant. There was significant interaction between (P≤0.01) generation and sex at 12 and 20 weeks of age, but at 4, 8 and 16 weeks of age it was not significant. There was not significant interaction between line and sex at 4 and 12 weeks of age where at 8, 16 and 20 weeks of age were highly significant. There was not significant interaction between generation and line and sex at all in the study. It was noticed inconsistent increments in shank length where it was 0.22, 0.32, 0.30, 0.31 and 0.21 (cm) in the first generation, while for the second generation it was 0.08, 0.31, 0.51, 0.52 and 0.54 (cm) at 4, 8, 12, 16 and 20 weeks of age, respectively.
2.2. Keel length at different ages (KL): The difference between generation in keel length was highly significant (P≤0.01) at 8, 12, 16 and 20 weeks of age. Also, there were highly significant differences (P≤0.01) between line in keel length at all ages of study, the selected line had longer keel length than the control line over generation and the selected line had longer keel length compared with the control line at 8, 12, 16 and 20 weeks of age. As for the effect of sex on keel length, the results showed that males keel length from 8 to 20 weeks of age were longer than that of females in the two line over generation. There were highly significant differences (P≤0.01) between sex at all ages of study. There were highly significant (P≤0.01) interactions between generation and line at 16 and 20 weeks of age, but at 8 and 12 weeks of age it was not significant. There were highly significant (P≤0.01) interaction between generation and sex at 12, 16 and 20 weeks of age. There was not significant interaction between line and sex at 8 and 12 weeks of age but at 16 and 20 weeks of age were highly significant (P≤0.01). There was not significant interaction between generation and line and sex at all ages of study. It was noticed inconsistent increments in keel length where it was 0.27, 0.35, 0.40 and 0.31 (cm) in first generation, while for the second generation it was 0.21, 0.40, 0.74 and 0.74 (cm) at 8, 12, 16 and 20 weeks of age, respectively.
3. Phenotypic correlations among growth measurements at different ages: It was noticed that there were positive and highly significant correlations between body weights, shank lengths and keel lengths at all age of the study. The highly significant and positive correlations between body weights at the different ages confirmed the importance of the correlation between weights at early and late ages during the growing period. Also, the highly significant and positive correlations between shank and keel lengths, at the different ages, coincided with that of body weight and reflect similar trend as body weight.
4. Carcass traits:
4.1. Live body weight: It was noticed that live body weight was higher in the selected line compared to the control line. There were highly significant differences (P≤0.01) between generation, line and not significant interaction between generation and line for live body weight.
4.2. Blood (%): There were not significant differences between generation, line and their interactions for blood percentage.
4.3. Feather (%): There were not significant differences between generation, line and their interactions for feather percentage.
4.4. Leg and head (%): Leg and head percentages of selected line were higher than control line and there were highly significant differences (P≤0.01) between generation, line, but the interaction between generation and line was not significant.
4.5. Viscera (%): There were highly significant differences (P≤0.01) between generation, while the difference between line and the interaction between generation and line was not significant for viscera percentage.
4.6. Giblets (%): There were not significant differences between generation and line, while the interaction between generation x line was significant (P≤0.05) for giblets percentages.
4.7. Carcass weight (g): carcass weight in selected line was higher than control line over generation and there were highly significant differences (P≤0.01) between generation and line for carcass weight.
4.8. Dressing (%): The selected line had higher dressing percentage (70.79%) than control line (67.57%) over generation. There were highly and significant (P≤0.01 and P≤0.05) between line and the interaction between generation and line, while the difference between generation was not significant for dressing percentage.
5. Egg production traits:
5.1. Age at Sexual Maturity (ASM): Age at sexual maturity were 161.47 and 165.44 days for control and selected line over generation, respectively and there were highly significant differences (P≤ 0.01) between generation, but the differences between line and the interaction between generation and line were not significant. The pullets of the second generation matured earlier than those in the first generation. selection to increase body weight at 8 weeks of age tend to delay the age at sexual maturity in the selected line pullets than that in the control line.
5.2. Means of Laying Rate (%): The means of laying rate for 7 successive laying periods (each 28 days) were 37.88 and 34.07 % for control and selected line over generation, respectively and there were highly significant differences (P≤0.01) between generation and line, but their interaction was not significant in laying rate. The control line had higher laying rate than that of selected line. It noticed that selection to increase body weight at 8 weeks of age tend to decrease laying rate in the selected line pullets than that in the control line.
5.3. Means of Egg Weight (g): The means of egg weight for 7 successive laying periods (each 28 days) was 47.84 and 48.30 g for control and selected line over generation, respectively and there were highly significant differences (P≤ 0.01) between generation and line, but their interaction was not significant. It noticed that selection for body weight increased egg weight in the selected line and the birds in selected line had laying heavier egg weight than those in control line.
5.4. Total egg mass (g): The total egg mass for 7 successive laying periods (each 28 days) was 4021 and 3927 g for control and selected line over generation, respectively and there were significant differences (P≤ 0.05) between generation and line, while the interaction between generation and line was not significant. It noticed that selection for body weight decreased total egg mass in the selected line and the birds in control line had higher total egg mass than those in selected line.
6. Egg quality traits:
6.1. Egg weight: means of egg weight at 48 weeks of age was 48.93 and 50.97 g for control and selected line over generation, respectively; there were highly significant differences (P≤ 0.01) between line in egg weight but the effect of generation and the interaction between generation and line was not significant. The weight of Dandarawi eggs in the present study was heavier than that recorded for Dandarawi breed in the previous studies.
6.2. Egg shape index: Means of egg shape index at 48 weeks of age was 77.77 and 77.51 % for control and selected line over generation, respectively; the effect of generation, line and their interaction were not significant.
6.3. Albumen percentage: Means of albumen percentage at 48 weeks of age was 56.13 and 57.08 % for control and selected line over generation, respectively. The effect of generation and the interaction between generation and line was not significant, while the effect of line was significant (P≤ 0.05).
6.4. Haugh Units: Means of Haugh units at 48 weeks of age were 86.21 and 87.32 for control and selected line over generation, respectively; the effect of generation and the interaction between generation and line was significant (P≤ 0.05 and P≤ 0.01), respectively; while the effect of line was not significant.
6.5. Yolk percentage: The yolk percentage at 48 weeks of age was 33.40 and 32.60 % for control and selected line over generation, respectively. The effect of generation, line and their interaction were not significant.
6.6. Yolk index: The yolk index at 48 weeks of age was 48.25 and 52.62 % for control and selected line over generation, respectively. The effect of generation was not significant, but there were highly and significant difference (P≤0.01 and P≤ 0.05) between line and the interaction between generation and line, respectively.
6.7. Shell percentage: The shell percentage at 48 weeks of age was 10.47 and 10.32 % for control and selected line over generation, respectively. The effect of generation, line and their interaction were not significant.
6.8. Shell thickness: The mean of shell thickness at 48 weeks of age was 0.37 and 0.38 mm. for control and selected line over generation, respectively. The effect of line and the interaction between generation and line was significant (P≤ 0.05), but the effect of generation was not significant.
In conclusion we can summarized our results that selection for body weight at 8 weeks of age led to improve directly body weight and conformation (shank and keel length) at different ages in Dandarawi chickens.
As for carcass traits, selection for body weight at 8 weeks of age led to increase carcass weight and dressing percentage at 12 weeks of age as an indirect response to selection.
As for egg production traits, selection for body weight at 8 weeks of age tend to delay the age at sexual maturity, decrease laying rate, increased egg weight and decreased total egg mass in the selected line pullets as an indirect response to selection.
As for egg quality traits in general, egg quality is slightly affected indirectly by selection for high body weight at 8 weeks of age in Dandarawi chicken.
Finally, it is advised to continue this program of selection for high body weight at eight weeks of age in Dandarawi chicken to achieve more improvement in growth measurements and other productive traits.