Effects of insulin-like growth factor I (IGF-I) polymorphism on bodyweight of Nigerian indigenous chickens

A total of 101 randomly selected birds from a population of 601 birds (obtained from a 3×3 diallel mating system involving normal, frizzle and naked neck Nigerian indigenous chickens) were used to evaluate the effects of insulin-like growth factor I (IGF-I) polymorphism on bodyweight. Blood samples for DNA analysis were collected at 20 weeks of age. IGF-I genotypes were identified using polymerase chain reaction (PCR)-RFLP method. Data obtained were analysed for frequencies and impact on body weight (BWT). Obtained results showed three polymorphic variants (designated AA, AB and BB) of the IGF-I gene. The overall frequencies for genotypes AA, AB and BB were 55.45, 37.62 and 6.93%, while alleles A and B were 74.26 and 25.74%, respectively. The analysis of the chicken IGF-I gene revealed that the chicken population was in Hardy Weinberg equilibrium, thus, samples were obtained from a large random mating population. IGF-I gene significantly (P<0.05) influenced BWT with the AA genotype having higher BWT than AB and BB at all ages (4-20 weeks) except at hatch. Therefore, 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.   Key words: Insulin-like growth factor I, polymorphism, bodyweight, indigenous chicken, PCR-RFLP.