GENETIC VARIABILITY AND ASSOCIATION OF PITUITARY-SPECIFIC TRANSCRIPTION FACTOR 1 GENE WITH PERFORMANCE TRAITS IN NIGERIAN LOCAL CHICKENS

Abstract

Recently, there is a trend on development and improvement of locally adapted chickens in the environment which would enable them to withstand the climatic condition and the endemic poultry diseases. This research was conducted to assess the genetic variability of Pituitary-specific transcription factor 1 (PIT 1) gene and its association with growth traits and breed effect on carcass, egg, haematology and biochemical traits in four breeds of Nigerian local and improved chickens namely: Frizzle feathered, Naked neck, Normal feathered and Noiler. A total of PIT 1 two hundred and forty (240) indigenous day-old chickens comprising of frizzle feathered (60), naked neck (60), normal feathered (60) and Noiler (60) were used. Data on growth performance, linear body measurements, baseline information on haematology and serum biochemical indices, carcass parameters, egg quality and laying performance and DNA analysis for polymorphism of gene in the four strains of Nigerian local chickens were collected and subjected to least squares means, correlation, multiple linear regression, allometry analysis and prediction using SAS 9.2 (Version 2008). DNA sequence alignment and sequence variation parameters, genetic diversities were determined using Mega 6.0 and DNA sp Version 5. Results obtained from the effect of breed on growth parameters were significantly (p<0.05) different but the effect of sex on growth parameters was not significant (p>0.05). The effect of age, strain, feather/coat colour and sex on body weight and linear body measurements from 4 to 16 weeks for the strains of chickens were significant (p<0.05) for all parameters measured except for comb length and wattle length. Prediction using multiple linear regression and allometry functions fitted into body weight and linear body measurements of the four breeds of local chickens in this study from 4 to 16 weeks revealed that wing length, shank length, shank circumference, drumstick length, drumstick circumference, nose to shoulder length, shoulder to tail length, body length, height at withers and breast girth could be the best variables used to predict body weight of frizzle feathered, naked neck, normal feathered and noiler chickens. The effect of strains and sex on haematological and serum metabolites was significantly (p<0.05) different. The effect of strains, sex and age on carcass parameter of local and improved Nigerian chickens at 13 weeks revealed significant effect (p<0.05) on all carcass parameters except for wing, head and neck weight. The effect of strain on short-term egg production characteristics of the four strains of chickens were significantly (p<0.05) different for all parameters. The effect of the polymorphism in PIT 1 gene on growth of the four strains of chickens revealed variations in polymorphism site across strains studied. Highest estimates of average evolutionary divergence over sequence pairs of chicken strains was observed in Noiler (0.666) and least in naked neck (0.01). Genetic distance in PIT 1 gene across the chicken strains studied revealed that the highest genetic distance was between frizzle feathered and Noiler (0.519) and the least genetic distance existed with normal feather and naked neck (0.073). The digestion of PCR fragment of SNPs in PIT 1 genotypes of g.457T>C produced fragment length of 626 bp for TT genotypes, 626 bp, 407 bp and 209 bp for CT, 407 bp and 209 bp for CC genotypes. CC genotype was more frequently observed in the four strains studied than other genotypes (0.736). C allele frequency (0.807) was higher than that of T allele frequency in all the SNPs. Results of this study could be used as baseline data for future improvement of Nigerian indigenous chicken strains. The effect of polymorphism in PIT 1 gene for the strains revealed a clearer understanding of the genetic diversity in PIT 1 gene across the strains of chickens evaluated.