الفهرس 
ABSTRACT
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Abstract
The present study included two parts, the first part was caried out at the Poultry Research Farm, Faculty of Agriculture, Assiut University, in a selection program for 8-weeks body weight over five successive generations to determine the direct genetic response in growth measurements, estimate the indirect response in egg production traits due to selection for high body weight at eight weeks of age, and estimate the selection differential, genetic response, and the realized heritability for all growth traits over five successive generations in Dandarawi chicken, while the second part was carried out in the Molecular Genetic Laboratory, National Gene Bank, Agricultural Research Center, Giza, to evaluate the diversity level and genetic relationship between two lines of Dandarawi chicken (selected and control) using microsatellite markers.
With regard to the first part of the study, involved 7066 pedigreed chicks obtained by mating 248 sires with 2452 dams through five successive generations and the chicks in each generation were divided into two lines, line (S) selected for high body weight at 8-weeks of age and control line (C), while in the second part, eighty individual birds from the 5th generation were used from the two lines (selected and control) of Dandarawi chicken (40 sample/each) and samples were amplified in a polymerase chain reaction (PCR) with nine microsatellite markers. The main results obtained in this study could be summarized as follow:
1. Inheritance of quantitative traits study in Dandarawi chicken:
1.1. Growth Measurements:
1.1.1. Growth Performance:
1.1.1.1. Body Weight (BW):
Differences in body weight between generations, lines and sex were highly significant (P≤0.01) at all ages during the study. The birds in the 4th generation were heavier in body weight when compared with the birds in the base, first, second, and third generation and superiority of selected line in body weight
compared with the control line in the different ages studied over generations. Body weight of males was heavier than that of females at all different ages over generations, and body weight of males and females in the selected line was heavier than their corresponding birds in the control line in all generations. Interaction between generations and lines and between generations and sex was highly significant (P≤0.01) at 0, 4, 8, 12, 16 and 20 weeks of age. There were highly and significant (P≤0.01 and P≤0.05) interaction between lines and sex and between generations, lines and sex at 0, 4, 8, 12, 16 and 20 weeks of age.
1.1.1.2. Shank Length (SL):
Differences between generations, lines and sex at 4, 8, 12, 16 and 20 weeks of age were highly significant (P≤0.01). The birds in the 4th generation had the longer shank length than the base, first, second, and third generation at the different ages. The birds of selected line (males and females) had longer shank length compared with control line (males and females) at 4, 8, 12, 16 and 20 weeks of age and it increased gradually in regular manner, as well as males were longer shank length than females at different ages. Interaction between generations and lines was highly significant (P≤0.01) in shank length at all ages of study. There were highly and significant (P≤0.01 and P≤0.05) interactions between generations and sex, between lines and sex, and between generations, lines and sex at 4, 8, 12, 16 and 20 weeks of age.
1.1.1.3. Keel Length (KL):
Differences in keel length between generations, lines and sex were highly significant (P≤0.01) at 8, 12, 16, and 20 weeks of age. The birds in the 4th generation had the longer keel length than the base, first, second, and third generation at different ages. The birds of selected line had longer keel length when compared with the control line at all ages of study and it increased gradually in regular manner, in similar trend males had longer keel length than females at the different ages. Interactions between generations and lines and between generations and sex were highly significant (P≤0.01) in keel length at all ages of
study. There were highly and significant (P≤0.01 and P≤0.05) interaction between lines and sex and between generations, lines and sex at 8 and 20 weeks of age, but it was not significant at 12 and 16 weeks of age.
1.1.2. Genetic Parameters:
1.1.2.1. Body Weight (BW):
Regarding the selection differential estimates of body weight, it were 1.19, 19.74, 17.66, 74.42, 79.43, and 125.87 gram in the base generation, while in the
4th generation it were 4.22, 90.76, 225.88, 292.77, 235.1, and 284.94 gram at 0,
4, 8, 12, 16 and 20 weeks of age, respectively, where the values of selection differential were positive and inconsistent over generations. After five generations of selection the cumulative selection responses for body weight were 4.75, 110.79, 223.80, 321.41, 297.89, and 323.53 gram at 0, 4, 8, 12, 16 and 20
weeks of age, respectively. Concerning the realized heritability estimates of selected body weight over five generations, it were 0.34, 0.45, 0.37, 0.35, 0.36,
and 0.30 at 0, 4, 8, 12, 16 and 20 weeks of age, respectively, and the realized heritability estimates of selected body weight varied from moderate to high estimates at the different ages of study. Also, the realized heritability estimates of body weight were decreased with the advance of age. Therefore, it is possible genetically increases body weight quickly at early ages without waiting for later ages to reduce the cost of breeding, save time and efforts.
1.1.2.2. Shank Length (SL):
Concerning the selection differential of shank length, it was 0.22, 0.32, 0.30, 0.31, and 0.21 centimeter in the base generation, while for the 4th generation, it was 0.63, 0.71, 0.89, 0.84, and 0.90 centimeter at 4, 8, 12, 16 and 20 weeks of age, respectively, and there is a divergent selection differential estimates over generations. Regarding the cumulative selection responses in shank length after five generations of selection at 4, 8, 12, 16 and 20 weeks of age were 1.05, 1.03, 1.16, 1.54, and 1.94 centimeter, respectively. As for the realized heritability
estimates of shank length over five generations, it had high estimates 0.52, 0.40, 0.38, 0.52 and 0.61 at 4, 8, 12, 16 and 20 weeks of age, respectively.
1.1.2.3. Keel Length (KL):
As for selection differential estimates of keel length, it were 0.27, 0.35, 0.40, and 0.31 centimeter in the base generation, while in the 4th generation it was 0.81, 1.01, 1.26, and 1.31 centimeter at 8, 12, 16 and 20 weeks of age, respectively, and the values of selection differential were positive and fluctuated over generations. After five generations of selection the cumulative selection responses in keel length were 1.12, 1.33, 1.93, and 2.35 centimeter at 8, 12, 16 and 20 weeks of age, respectively. Regarding the realized heritability estimates for keel length over five generations, it were 0.44, 0.43, 0.46, and 0.52 at 8, 12, 16 and 20 weeks of age, respectively, and the estimates of realized heritability for keel length at different age of study were high.
1.1.3. Phenotypic correlations between growth measurements at different ages:
The phenotypic correlations between body weights, shank lengths and keel lengths were positive and highly significant at the different ages in this study, which indicated that it can be possible to carry out a selection program at an early age to improve growth measurements in Dandarawi chicken.
1.2. Egg production traits:
1.2.1. Age at Sexual Maturity (ASM):
The pullets in the first generation matured earlier (154.26 day) than that in the base, second, third, and fourth generation (171.52, 161.14,162.60, and 164.88 day, respectively).The pullets in the selected line matured later (167.40 day) than the pullets of the control line (159.46 day) over generations. There were significant differences between generations, lines, and their interaction (P≤0.01).
1.2.2. Average of Laying Rate (%):
The pullets of the 4th generation had higher laying rate (42.33 %) than that in the base generation (35.32 %), and the selected line had lower laying rate
(36.84 %) when compared with the pullets in the control line (40.46 %). There were highly significant differences (P≤0.01) between generations and lines but their interaction did not significant.
1.2.3. Egg Weight (g):
In the 4th generation, the pullets had laid heavier egg weight (50.18 gram) than that in the base generation (47.70 gram) and the pullets in selected line had laid heavier egg weight (50.12 gram) when compared with the pullets in the control line (48.00 gram). There were highly significant differences (P≤0.01) between generations, lines, and their interaction in egg weight.
1.2.4. Egg Mass (g):
The pullets of the 4th generation had higher egg mass (4163.27 gram) than that in the base generation (3302.14 gram), and the pullets in the selected line had lower egg mass (3618.98 g) than in the control line (3806.48 g). There were significant and highly significant differences (P≤0.05 and P≤0.01) between generations, lines, and their interaction in egg mass.
In conclusion we can concluded our obtained results in this part that selection for body weight at 8 weeks of age led to improve directly growth measurements (body weight, shank, and keel length) at the different ages in Dandarawi chicken. The realized heritability estimates varied from moderate to high (0.30- 0.61) for all growth traits studied over generations at different ages. With respect to egg production traits, selection for body weight at 8 weeks of age led to delayed age at sexual maturity, that was negatively associated with selection, and resulted in decreased laying rate and egg mass, but tended to increase egg weight in the selected line pullets as an indirect response to selection. Ultimately, the finding in the current study, revealed that the selection for high body weight at 8-weeks of age led to positive changes for growth measurements, and it is expected that after several generations of selection, Dandarawi chicken will be advantageous as a domestic chicken breed for body weight. So, it
necessary to continue the program of selection to achieve more improvement for growth performance and other productive traits in Dandarawi chicken.
2. Molecular genetic study of Dandarawi chicken in the 5th generation:
The genetic diversity within two examined chicken’s lines (selected and control Dandarawi) were identified by the number of alleles per locus for each one, specific alleles, effective number of alleles, expected, and observed heterozygosity.
2.1. Allele frequency:
The highest allele frequency overall loci was 0.21 and 0.28 at locus MCW0069 in selected and control Dandrawi lines, respectively, whilst the lowest allele frequency was 0.01 at LEI0094 locus for selected Dandrawi and at MCW0081, MCW0330, ADL0112, and MCW0103 loci for control Dandrawi.
2.2. Polymorphic Information Content (PIC):
PIC value for selected Dandarawi line ranged between 0.95 for locus MCW0034 and 0.87 for locus MCW0069, while for control Dandarawi line it was ranged between 0.94 for loci (MCW0034, ADL0112, LEI0094) and 0.82 for locus (MCW0069). Also, all markers used in this study were highly informative PIC values for selected and control Dandarawi lines
2.3. Number of alleles, specific alleles, shared alleles, total number of alleles, and effective number of alleles:
A total of 326 alleles were detected across 9 loci in the two lines of Dandarawi chicken (164 and 162 allele) for selected and control, respectively, with a mean number of 36.22 alleles per locus and ranged from 25 (MCW0069) and 47 (MCW0034). The lowest number of alleles overall loci were 11 alleles in control Dandrawi at locus MCW0069, while for the selected Dandarawi locus MCW0034 was the highest one that was 25 alleles which revealing higher polymorphism when compared with the control Dandrawi. The all selected loci in the present study for the two Dandarawi chicken lines were reliable and informative because number of alleles per locus were more than four.
Regarding specific number of alleles, a total of 168 out of 326 alleles (51.53%) were detected overall loci (9 microsatellite loci) with the two lines of Dandarawi chicken (85 and 83 specific allele) for selected and control, respectively. These specific alleles could be used as a breed fingerprint, even if only one allele was used for one locus and could be strongly utilized as a molecular tool in a fingerprint analysis of Dandarawi chicken. Concerning the total number of shared alleles, 79 out of 326 alleles (24.23%) with a mean of 8.77 were detected overall loci in the two lines of Dandarawi chicken.
With regard to the effective number of alleles (ENA), the lowest effective number of alleles was 7.84 for locus MCW0069 when the expected heterozygosity was 0.88 and 0.83 with selected Dandarawi and control lines, respectively, while the highest effective number of alleles was 26.01 for locus MCW0034 when the expected heterozygosity was 0.96 with both selected Dandarawi and control lines.
2.4. Observed heterozygosity (HO), Expected heterozygosity (HE), and Inbreeding Coefficient (IC):
Selected Dandarawi line had the highest mean of observed heterozygosity (HO) 0.45, while the control Dandarawi line had the lowest with a mean of 0.38, overall loci. Locus MCW0034 had the highest mean of (HO) 0.94 and 0.81 for selected and control Dandarawi, respectively. Overall loci the selected Dandarawi line had the highest mean of expected heterozygosity (HE) 0.93, while the control Dandarawi line had the lowest 0.92. Locus MCW0034 had the highest mean of expected heterozygosity (HE) 0.96 for the two lines of selected and control Dandarawi, whereas locus MCW0069 had the lowest mean of (HE) 0.88 and 0.83, respectively.
With regard to the inbreeding coefficient (IC), it was 0.52 and 0.59 for selected and control Dandarawi lines, respectively. The mean of fixation indices (FIS) was 0.53 and 0.59 for selected and control Dandrawi lines, respectively.
according to the ovearall mean of (FIS=0.56) that was more than 0.4, the breed of Dandarawi chicken is critically endangered.
2.5. Genetic analysis:
The variability percentage among lines was (4.08%) significantly lower than among individuals within lines (86.42%), while within individuals the variability percentage was (9.50%). Therefore, a slight genetic diversity in Dandarawi chicken lines were occurred. Cluster analysis based on genetic distance indicated that the relationship between the studied lines was more genetically related to each other.
It could be concluded that the high polymorphism of the nine microsatellite loci observed in this study confirmed that microsatellite markers could be strongly utilized in future studies as a molecular tool in fingerprint analysis and to assess the genetic diversity for other local chicken strains. Also, the microsatellite markers were used to serve genetic diversity on multiple levels, including conservation and for future improvements in Dandarawi chicken breed. Also, this approach could be useful in a future MAS (marker-assisted selection) systems for genetic improvement in Dandarawi chicken without waiting for several generations which reduce the cost of breeding, save time and
efforts.