ABSTRACT
An experiment was conducted using a total of 601 chicks hatched from a diallel crossing of three genotypes (Normal [N], Frizzle [F] and Naked neck [Na]) of Nigerian indigenous chickens to evaluate the effects of genetic differences on growth traits, reproductive traits, haematological and biochemical parameters. The possibility of using IGF-I gene as a candidate gene in selection for body weight was also investigated. The chicks used in this study were hatched from a total of 90 chickens comprising of 25 hens and 5 cocks for each of the three genotypes. A mating ratio of 1 male: 5 females was employed. Blood samples for haematological, biochemical and molecular studies were collected at 20 weeks of age. Data collected were subjected to general linear model procedure of Statistical Analysis System (SAS) after been corrected for significant effects of hatch of birds using the least squares constants. Furthermore, data on body weight was analysed using complete diallel analysis. The results revealed that body weight (BWT) was significantly (P<0.01) influenced by genetic groups with the Frizzle-Naked (FNa) having the best performance at all ages (4 - 20 weeks) except at hatch, with a mean final BWT at 20 weeks of 1173.16g. It was followed by its reciprocal, Naked-Frizzle (NaF) with a mean final BWT of 1161.88g. Variations in breast girth (BG) and tibia length (TL) were influenced in part by BWT with the crosses of the F ร“ Na showing superiority as opposed to the other combinations of F ร“ N and N ร“ Na. The FNa also attained sexual maturity at 148.50 days and was only next to Na (142.50 days) followed by its reciprocal, NaF (149.50 days). Furthermore, the FNa gave the best estimates for heterosis and specific combining ability (SCA) while the F and NNa gave the best estimates for general combining ability (GCA) and reciprocal effect (RE), respectively. Some of the haematological and biochemical parameters were significantly(P<0.05) affected by the genetic groups but showed no definite trend with respect to BWT and sexual maturity except lymphocyte and heterophil counts. Three polymorphic variants (AA, AB and BB) of the Insulin Growth Factor I (IGF-I) gene were observed. Furthermore, the observed genotypic and allelic frequencies showed that the population of Nigerian indigenous chickens conformed to Hardy Weinberg equilibrium based on IGF-I locus; thus samples were obtained from a large random mating population. IGF-I gene significantly (P<0.05) influenced BWT with the AA genotype having heavier BWT than AB and BB at all ages (4 - 20 weeks) except at hatch. Therefore, the F genotype as sire and the Na as dam provided the most suitable combination for improved BWT and age at sexual maturity. Furthermore, the use of Na genotype as dam was also more suitable in order to take advantage of the sex-linked/maternal effect. In addition, the effect of IGF-I gene on BWT indicated that it could be appropriate as a candidate gene in selection for BWT in Nigerian indigenous chickens
