RESUMO
High ambient temperatures pose serious productive challenges to poultry farmers in the tropics with adverse consequences such as reduced egg production. A study was undertaken to assess the effect of naked neck (Na) and frizzle (F) genes on the performance of F2 and F3 generations of crosses of commercial and indigenous chickens in Ghana. One thousand, five hundred and sixty-five (1,565) eggs distributed in a randomized complete block design comprising 4 genotypes and 15 hatches were used for the first study. The eggs were produced from 33 each F2 crossbred normal-feathered (nanaff), naked neck (Na), frizzle (F) and both (Na and F) alleles carrying chickens to determine the effects of these genes on fertility and hatchability. Data were analysed using the mixed model procedure of GenStat statistical software. Eggs from birds with the heat-tolerant genes, either in the single or double doses, were significantly more fertile than those from birds without the genes. Eggs of birds carrying the F allele had significantly (P < 0.05) higher hatchability than eggs from birds carrying the Na allele.Subsequently, 199 F3 crossbred chickens obtained from six hatches generated by the F2 generation were used for the evaluation of growth, egg production, haematological and blood biochemical parameters. The genotypic groups were normal feathered (nanaff), homozygous naked neck (NaNaff), heterozygous naked neck (Nanaff), homozygous frizzle (nanaFF), heterozygous frizzle (nanaFf), double homozygous naked neck-frizzle (NaNaFF) and double heterozygous naked neck- frizzle (NanaFf). The Nanaff recorded a significantly (P < 0.05) heavier day-old body weight compared to all other genotypes except the NaNaff birds.The nanaff genotype reached sexual maturity significantly earlier than all other genotypes. Hen day egg production and egg weight were also significantly higher in nanaff birds compared to birds carrying either Na or F allele, or both alleles. All birds carrying the naked neck and frizzle genes had significantly higher packed cell volume (PCV) concentration than the nanaff genotype. The Nanaff genotype recorded a significantly higher blood haemoglobin concentration compared to the nanaff, nanaFf and NaNaFF ones. However, birds carrying the thermoregulatory genes recorded significantly (P < 0.05) higher haemoglobin values except for the heterozygous frizzle. The thermoregulatory genes are of importance in chicken populations in Ghana as they positively influence percentage fertility of chicken eggs and PCV concentrations of chicken blood.