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Effects of Crossbreeding and Inbreeding on Growth Performance, Age at Sexual Maturity and Chromosome Morphology of Three Genetic Groups of the Philippine Native Chickens (Gallus gallus domesticus Linn.)
Dissertation Abstract:
Three genetic groups of the Philippine native chickens (Banaba, Paraoakan, and Bolinao) and their crosses were used in this study. They were subjected to a 3x3 full diallel cross design to determine heterosis and combining abilities for growth performance and age at sexual maturity. The F1 progenies of the Banaba x Paraoakan cross consistently showed the highest body weight with high heterosis especially at 8, 10, 12, 14, 18, and 20 weeks of age.
General combining ability, specific combining ability and reciprocal cross effects on body weight were significantly different (p < .05). Both the Banaba and Paraoakan groups showed relatively high positive values for general combining ability indicating that the body weight at ages considered were governed primarily by additive gene action.
In a separate experiment, a total of 180 heads of native chickens were used for a one-year inbreeding study. These chickens were produced from four different kinds of inbreeding, namely: parent offspring, full sib, paternal half sib, and maternal half sib mating involving the three genetic groups of the Philippine native chickens.
Results indicated that mating of closely related chickens under different systems of mating in one generation showed a potential problem to the body weight of the three genetic groups studied. The Banaba group exhibited delay in their age of sexual maturity following inbreeding under different systems of mating. The delay varied from one to three days of about 1.4, 1.2, 0.9, and 2.0 percent under parent offspring, full sib, paternal half sib, and maternal half sib mating, respectively. The Paraoakangroup showed the delay of one to four days or about 1.1, 2.8, and 0.9 percent under the full sib, paternal half sib and maternal half sib mating, respectively.
A total of 48 heads of adult chickens were sacrificed. The bone marrow cells were analyzed for karyotyping. The Banaba, the Paraoakan and the Bolinao chickens possessed seven identifiable macrochromosomes including the Z and W sex chromosomes. The first and second chromosome complement had metacentric type. Chromosomes 3 and 5 were acrocentric, while chromosome 4 was submetacentric. Chromosome 6 was telocentric. The W chromosome was metacentric, while the Z chromosome was telocentric. The Bolinao had the highest centrometric index (37.59) followed by Banaba (36.62) and Paraoakan (35.80). The highest arm ratio was noted in Paraoakan with 1.80, followed by Banaba and Bolinao with 1.74 and 1.67, respectively. The length of chromosome complement of the three genetic groups did not show significant variations except for chromosome 4. The longest W and Z sex chromosomes noted in the Banaba x Paraoakan cross might contribute to the superiority of this particular cross over the other hybrid.